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Brian Vogel
Grand Master
Username: guyslp

Post Number: 356
Registered: 6-2009
Posted on Wednesday, 08 May, 2013 - 09:57 am:   Edit PostDelete PostView Post/Check IP

. . . clearly, I don't!!

On the previous thread about my spark plugs Geoff Wootton offered the following as his suggestion as to how I should proceed:

1. Compression test each cylinder

2. Set ignition dwell angle and timing to factory specs

3. Balance carbs and set the mixture strength


I'll openly admit that I'm skipping #1 since I have almost no reason to believe that compression is a problem.

After starting to dig into the workshop manual it appears that #2 is going to require a thread of its own to advance my knowledge.

I had every intention of trying a slight tweaking of mixture strength to weaken it a bit today, but reality has set in.

First, a snippet from the workshop manual:
HIF7 Float Chamber & Mixture Strength Adjustment

I am having a great deal of difficulty with perspective on this particular figure. It seems to me to be looking into the A Bank carb from the right side of the car, with most of the things shown being inboard from the connector plate shown. I've tried to mark this illustration and then carry this over to his photo from my car:

LRK37110 - A Bank Carb

Based on the workshop manual figure I would expect that the mixture/jet adjusting screw would be in a tube, behind a cap of some sort, about at the level shown in the figure, but I can find nothing anything like that on the real thing. In shining a light into any of the tubular bits sticking out of the side of the A Bank carb that faces the front of the car I can't see a screw in any of them nor any sort of cap. They're all dead ends. The screw I have marked with the red arrow seems entirely too low and unprotected to be the mixture/jet adjustment screw.

Can anyone offer definitive guidance here. Even trying to get photos of these bits is a challenge, and it's worse on the B Bank side where the respective sides of the carbs are reversed.

Also, how serious is that warning about not touching the mixture adjustment on this particular version of the SU carb? I have the feeling it's already been done before, but still. . .

Brian
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Benoit Leus
Frequent User
Username: benoitleus

Post Number: 65
Registered: 6-2009
Posted on Wednesday, 08 May, 2013 - 05:13 pm:   Edit PostDelete PostView Post/Check IP

Hi Brian,

I've done it last year and the mixture screw is indeed a different one. If my memory serves me right it's somewhere at left/rear of the A carb and front/left of the B carb.
I can take al look at my car tonight and be more precise.

I believe that the red arrow in your picture points at the screwhead of the pin keeping the float in its place.

Benoit
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Paul Yorke
Grand Master
Username: paul_yorke

Post Number: 1013
Registered: 6-2006
Posted on Wednesday, 08 May, 2013 - 05:51 pm:   Edit PostDelete PostView Post/Check IP

Brian,
what are you trying to cause by adjusting them?

are you proficient in setting up the older non HIF carbs?

I confess that I haven't re read your posts and do not know if you have a set of balancing tools and a gas analyzer to hand , but running before you can walk springs to mind .

The warning is serious because you have a 99% chance of setting the carb wrong , amd a 1% chance of getting it right. There are two carbs. adjusting one affects the other. The oaths doesn't look good for the un initiated. Probably not something to be learnt froo the RR manual?!

Benoit, I think it was you that had a year of fighting with them before getting them right?

These carbs are brilliant and there is no reason for them to go more than am 8th of a turn of adjustment.

If it does , either There is something wrong elsewhere or somebody has been `playing ` with it and messed it up.

Is the tin plug still over the adjusting screw keeping it safe the reason you can not find it?

Do not screw it in too far or you will damage tin bi metallic spring .

post close up photos of your jets so we get am idea of where they are set atm.

There are books, videos , and tutorials about that give a novice a fighting chance !

Good luck and be careful. :-)
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Benoit Leus
Frequent User
Username: benoitleus

Post Number: 66
Registered: 6-2009
Posted on Wednesday, 08 May, 2013 - 06:52 pm:   Edit PostDelete PostView Post/Check IP

Indeed Paul,
it took me a year before I got the carbs to run smoothly.
I fiddled with them because my car ran rough anyway. In the end I rebuilt the carbs and had a professional do the final tuning as I couldn't get it right myself.

Benoit
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Brian Vogel
Grand Master
Username: guyslp

Post Number: 357
Registered: 6-2009
Posted on Wednesday, 08 May, 2013 - 11:54 pm:   Edit PostDelete PostView Post/Check IP

Paul,

The car runs relatively rough at idle and is clearly running really, really rich based on what I can smell in the exhaust fumes. They are aromatic enough to burn your eyes if you can get the car to stay on at idle (it will often stall) and you hang out in the garage even though the door is open.

I've changed out the plugs, so that does not appear to be the problem, and the difference, if any, is minimal.

If you press the accelerator and get the engine going it runs quite smoothly, but then if you let off the gas, even if you do it very slowly, the car will always stall when it comes back down to idle speed.

When the choke is set the car will definitely start and run, but you can tell when the choke kicks off. At that point the engine stumbles a bit and sometimes "finds its footing" and runs but at other times stalls. Even in the "finds its footing" situation, if you depress the accelerator and then let off the gas you will get a stall.

I am more than willing to look elsewhere first, I just don't know exactly were else I should look first. This is an area of "revival from the dead" that I did not have with my other car so it's virgin territory for me. I need all the guidance I can get.

As a point of interest, someone must have set the timing at one point or another (but who knows when). The 15 mark has been painted with a white line to make it much easier to see with a strobe light.

Although this car was well maintained, by a dealer, for most of its life I believe it suffered at the hands of someone utterly incompetent in the last few years before I got it. Just the fact that one of the very heavy lines into the ammeter shunt had been cut was a big red flag in that regard.

In November 2004, records from Bentley High Point note that the carbs were overhauled, the needle valves and seats were replaced, the floats were adjusted, and all the fuel filters were replaced. That was when the car had 23,061 miles on it. I took possession of the car in January 2012 with 26,537 miles on it. The poor thing hadn't even gone 500 miles in a bit over 7 years.

My gut is telling me that whatever this issue is that it is probably easily fixed, at least for someone who's been through it before and recognizes what the signs are saying. Unfortunately for me, that's not me.

Brian
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Jeff Young
Prolific User
Username: jeyjey

Post Number: 144
Registered: 10-2010
Posted on Thursday, 09 May, 2013 - 12:09 am:   Edit PostDelete PostView Post/Check IP

Hi Brian,

Remember that there are two idle stops: the fast-idle cam (which is set when you press the accelerator before starting the car, and whose cam position is controlled by the automatic choke), and the normal idle stop screw. The fast idle cam is behind the A-bank carb, while the idle stop screw is on the front of the B-bank carb.

Does aromatic smell always mean rich-running? (Pardon my ignorance here, I'm no tune-up specialist. It just seems that if the mixture were far too lean, or the idle far too low that some cylinders might not fire, passing through their entire fuel charge unburnt, which would produce an aromatic smell.)

Anyway, try bumping up the idle stop screw on the front of the B-bank carb and see if it does anything.

Cheers,
Jeff.
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Jeff Young
Prolific User
Username: jeyjey

Post Number: 145
Registered: 10-2010
Posted on Thursday, 09 May, 2013 - 12:22 am:   Edit PostDelete PostView Post/Check IP

Fast idle mechanism (which overrides the other when the choke is on):
fast idle mechanism

Idle stop screw (which sets the idle speed when the choke is off):
idle stop screw
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Brian Vogel
Grand Master
Username: guyslp

Post Number: 358
Registered: 6-2009
Posted on Thursday, 09 May, 2013 - 02:41 am:   Edit PostDelete PostView Post/Check IP

Jeff,

Thanks very much. I'll definitely look at these things today.

When I first started posting about this issue a while back I also got this advice from someone on the RROC-US (I think) forums, which I'll reproduce here in its entirety:

On this car the choke butterfly was sticky and would not fully open (keeping the mixture too rich) until I revved the engine and the airflow would force it open. I pulled the intake piping from the air cleaner to the choke,cleaned around the butterfly with carb cleaner, lubed the shaft and external linkage with LPS #1 and Bob's your uncle.
Puttering around and running rich may well have fouled some plugs. I would install a new set of Champion RN14YC's (that ought to start a new thread on spark plugs!), check that the carbs are ballanced (I'm assuming you have HIF7s) and adjust the richness on both. An easy way to check the ballance is to use 2 6" lengths of wire (1/16 gas welding rod is great). Remove the dampers (the plastic thumb knobs on top of the vacuum domes). Bend one end into a triangle so each rod fits securely into the top of each piston, and point and bend the other ends so they are even with each other. Start the engine and if they are no longer even, adjust the intermediate link on the radiator side of the carbs until they are. The jet adjustment is a horizontal screw located just below the fuel filters. The carbs are the same,l&r so that is toward the rear of the car on the right and toward the front on the left just behind where the inlet air pipes bolt on. Screwing the screw in enrichens the mixture, and out leans it. Final idle adjustment is on the right carb, a slotted screw with a lock nut high on the forward side where the carb bolts to the manifold. This is far from the proper procedure but it will tell you in an hour or so if there are more serious problems you need to address.


At the moment I plan on only looking at the choke butterfly and the linkages, which leads me to another couple of questions. Comments on any other part of the "quick and dirty" checks are welcome, too, but they're not on the list over the next few days, at least.

1. What is the appropriate cleaner to use on the linkages?

2. I have seen very mixed opinions about lubrication on the throttle linkage, choke linkage, etc. What, if anything, is the appropriate lubricant to use on these? [Straight from the source, LPS 1 Greaseless Lubricant]

Brian
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richard george yeaman
Frequent User
Username: richyrich

Post Number: 86
Registered: 4-2012
Posted on Thursday, 09 May, 2013 - 03:12 am:   Edit PostDelete PostView Post/Check IP

Hi Jeff.
Thanks for that, Very informative, I wasn't aware that there was two idle screws on these carbs, I was actually using the A bank adjuster to set the idle speed, I had been using Gunson Colortune to check my fuel/air mixture seems to do a good job.

Cheers.

Richard.
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Jeff Young
Prolific User
Username: jeyjey

Post Number: 146
Registered: 10-2010
Posted on Thursday, 09 May, 2013 - 03:29 am:   Edit PostDelete PostView Post/Check IP

I also had a choke-held-closed problem, but mine was due to a faulty thermal delay unit. In any case, if the choke was being held closed, I think the symptoms would be different (it would probably idle fine, although very rich and with black smoke out the tail pipe, but would have no pickup until you really layed in to the throttle).

Personally I use WD40 to both clean and oil the throttle linkages. But that's mostly because I don't have any LPS 1. ;)

Cheers,
Jeff.
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Brian Vogel
Grand Master
Username: guyslp

Post Number: 360
Registered: 6-2009
Posted on Thursday, 09 May, 2013 - 09:58 am:   Edit PostDelete PostView Post/Check IP

Jeff & Richard,

Well, it gets even more interesting regarding "what's where" once you start poking around and then realize that there are tons of delivery market specific features related to the carbs and lots else in the engine bay. All of this is documented in Chapter U (see my other post on this). I very quickly figured out that the idle stop screw on LRK37110 is not in front of the B Bank carb but instead it's in front of the A Bank Carb and the linkage is arranged differently.

I started the car again today and am hoping that "listening is worth a thousand words" for those who can stand to do it. The MP3 recording of LRK37110 starting and, around 6:40, stalling after I let off of the accelerator, can be downloaded here.

The most pertinent parts are at the very beginning and very end, but I'm sure there's something to be gleaned for those who've "heard this kind of thing before" from what goes on in the middle, too.

I can report that there is a very slight change since the new spark plugs have been installed, but it is very slight. The exhaust fumes are very strongly scented, and have a very thin, white quality to them. The smell, and appearance, has nothing in common with "blue smoke" from burning oil.

I used carb cleaner today to clean all of the linkages that I could get a good squirt on, including the exterior connection to the choke butterfly. When I set the choke the fast idle cam definitely sets as it should.

I didn't let the car run long enough to heat up enough to have the choke come off that way, but it did get deactivated when I gave it gas after approximately 6 minutes and then slowly let off the gas. I wasn't quite as slow at the very end of releasing the pedal, but the result is the same even if I go even more slowly. Be aware that this car is very noisy secondary to multiple exhaust leaks, which makes things sound worse than I think they are. You can tell that the engine really smooths out when given additional fuel and it speeds up.

I also hooked up my timing light for the first time today just to see if it works. It does and I'm presuming I could use this as a quick and dirty way to check whether an electrical impulse to create spark is being generated on each HT line. I only played with A1 today, since that's the one you really use to do timing on. It's a bit of a challenge getting the electrical connection for the light with the battery being located in the boot/trunk. I ended up using a set of jumper cables as an extension cord so I could get power to the lamp. This leads to another question that's specific to this application: Could I make a dedicated extension cord for this purpose from something far less substantial than jumper cables? It seems the wires that go to the light itself are standard "household lamp" gauge wires, so I'd think I could use something about that gauge to get power from the battery to the lamp. I need a bit more reach than I can easily get using today's technique.

Brian
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Brian Vogel
Grand Master
Username: guyslp

Post Number: 363
Registered: 6-2009
Posted on Wednesday, 15 May, 2013 - 12:00 pm:   Edit PostDelete PostView Post/Check IP

Well, the saga continues. Since so much intertwined territory has been covered on this thread that I'm going to continue here, though most of it will not be directly carb related.

Today I fired up the car again and once I had gotten the engine going at fairly high speed I very, very slowly eased off of the accelerator. As I came back down to very near to idle speed (which a laser tachometer indicates is very near to 600 RPM) I noticed a distinct "skip" that I think may be a miss. The reason I'm not certain is my experience when my Jag has a bad ignition coil causing a miss: it runs so horribly and the miss makes things so rough and out of whack that there's no doubt what's going on. On this car, the idle can be quite rough, the engine will also rock some, I have the very strong exhaust smell but it doesn't seem "rough enough" to be a miss.

How does a miss on these cars present?

One of the things previously suggested was to measure the resistance in the spark plug wires. What reading should I expect on the multimeter for a "good" versus a "bad" wire? I know that good should have low resistance, but I have no idea how low.

If the plug wires turn out to be OK, and I can confirm a miss somehow, what would the next logical thing be to attempt to rectify it?

Brian, either thinking one step ahead or getting ahead of himself (and even I can't decide on that one)
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Patrick Lockyer.
Grand Master
Username: pat_lockyer

Post Number: 851
Registered: 9-2004
Posted on Thursday, 16 May, 2013 - 04:36 am:   Edit PostDelete PostView Post/Check IP

If the plug wires turn out to be OK, and I can confirm a miss somehow, what would the next logical thing be to attempt to rectify it?

1 Distributor cap.
2 coil.
3 exhaust valve.
4 piston u/s.
5 head gasket.
Best bet is to do the correct procedure ie engine analyser and a leak down test.
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Paul Yorke
Grand Master
Username: paul_yorke

Post Number: 1016
Registered: 6-2006
Posted on Thursday, 16 May, 2013 - 06:25 am:   Edit PostDelete PostView Post/Check IP

or it could be the mixture.
Timing
vacuum capsule
vacuum hose
weakener
bob weights seized

it's sort of a circle of possible faults with the possibility of there being a few faults.

start with the cheapest and quickest ones and work forward from there.

good luck with her:-)
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Benoit Leus
Frequent User
Username: benoitleus

Post Number: 69
Registered: 6-2009
Posted on Thursday, 16 May, 2013 - 07:22 am:   Edit PostDelete PostView Post/Check IP

Brian,

the problems you discribe sound exactly the same as the ones I had with my car. Rough idle and "missing".
I checked and replaced all ignition components, without result. Pauk Yorke insisted it was probably fuel related and of course he was right. It was only after I rebuild the carbs and then had them tuned that it ran smoothly again.

Good luck !

Benoit
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Patrick Lockyer.
Grand Master
Username: pat_lockyer

Post Number: 853
Registered: 9-2004
Posted on Thursday, 16 May, 2013 - 08:31 pm:   Edit PostDelete PostView Post/Check IP

"I noticed a distinct "skip" that I think may be a miss".

If it is a cylinder missfire then the carb would be ok as it would effect all four cylinders.
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Paul Yorke
Grand Master
Username: paul_yorke

Post Number: 1017
Registered: 6-2006
Posted on Thursday, 16 May, 2013 - 09:32 pm:   Edit PostDelete PostView Post/Check IP

although if carbr are slightly out it can be smooth for a second then skip a beat then smooth for a second again.
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Brian Vogel
Grand Master
Username: guyslp

Post Number: 368
Registered: 6-2009
Posted on Friday, 17 May, 2013 - 07:04 am:   Edit PostDelete PostView Post/Check IP

Paul,

At true idle speed (around 600 RPM) it's never smooth. When you give the car fuel after a certain point not too terribly far above idle things smooth out entirely and stay that way as long as you've got your foot on the accelerator.

On the way back down in speed, just a bit above idle speed, is where I really detect a miss, as everything else is relatively "smooth enough" to tell it's happened. Once you let off the gas entirely the car typically stalls. It will, however, generally idle for at least 10 minutes or so (sometimes more) if you do not ever increase the engine speed. It seems to get happier once the choke kicks off, but can be quite cranky at the "choke trying to kick off" point.

The more people offer me (and, even though I'm about to complain, it's *not* about what's offered) the more convinced I become that there are probably 100 variables and I'll have to go through all 100 before hitting the right and incredibly simple fix.

Brian
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Paul Yorke
Grand Master
Username: paul_yorke

Post Number: 1018
Registered: 6-2006
Posted on Friday, 17 May, 2013 - 08:24 am:   Edit PostDelete PostView Post/Check IP

unfortunately Brian , that's too true.

And unfortunately one variable effects other ones.

Have you tried setting the held to 650 and see picture happens with use?

Experience can but most of the steps out . . but unfortunately you can not acquire that without spending the time.

Like I said somewhere, start with the easier cheers things and work from there.

Is there not an MG or Austin , or Jaguar guy nearby used to SU carburettors nearby who could come and play with you?
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Brian Vogel
Grand Master
Username: guyslp

Post Number: 369
Registered: 6-2009
Posted on Friday, 17 May, 2013 - 09:28 am:   Edit PostDelete PostView Post/Check IP

Paul,

This sentence, Have you tried setting the held to 650 and see picture happens with use?, isn't making sense to me. What I'm "translating" out of it is a question asking whether I've set the idle speed to 650 via the idle set screw and seen what happens. If that's correct then the answer is "not yet."

I only wish there were local others I could confab with on this and other issues, but alas, if there are, I haven't met them yet. I'd also probably drive them crazy if they're of the "let's try this, no, let's try that, no, let's try this third thing," variable tweaker camp. I tend to be very slow and deliberate in considering what I'm going to change and then changing only one thing at a time.

Brian
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Brian Vogel
Grand Master
Username: guyslp

Post Number: 372
Registered: 6-2009
Posted on Sunday, 19 May, 2013 - 02:07 pm:   Edit PostDelete PostView Post/Check IP

More to report after today's session in the garage.

Checking the individual spark plug wires via the timing light to see if they were all having spark sent to them indicated that they are. A check of the idle speed with a laser tachometer, using the harmonic balancer as the target indicated that the speed was slow by anywhere between 75 RPM and 125 RPM as the idle fluctuates. This led me to start looking at the idle speed adjusting screw as the first order of business.

First, Figure U33, the throttle linkage for U.S. and Canada delivery cars with pollution control, for reference:

Figure U33 - Throttle Linkage

Here's what I found:

Idle Adjusting Screw - Overhead View

and

Idle Adjusting Screw - View from Locking Nut End

I ended up removing the lock nut and running the screw in a bit more, but clearly something's "off" here if you can't get it to touch the stop as it was already adjusted. I'm wondering if this is the original screw or not, based on the figures in the workshop manual. This helped a little, but not much.

The car had been running for a while, so the choke had kicked off. At this point I decided to try giving the control rod for the choke butterfly a slight, and I do mean slight, push downward. Well, lo and behold, this caused an almost instant increase in engine speed and smoothing out of the roughness. This was consistent with what I was able to produce by giving the car gas, but in this case I definitely was not doing that. If I'm understanding what's happening when you push down on this rod it causes the air flow to the carbs to be slightly reduced and the mixture to become slightly richer as a result. A while back someone suggested that my problem might not be an overly rich mixture, but one so lean that all was not well as far as ignition, particularly when the engine is cold.

Is resetting the fast idle per the instructions in Chapter U, page U5-2, PDF page 512, a logical next step based on today's findings?

Brian
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Paul Yorke
Grand Master
Username: paul_yorke

Post Number: 1019
Registered: 6-2006
Posted on Sunday, 19 May, 2013 - 03:57 pm:   Edit PostDelete PostView Post/Check IP

Brian,did you ever synchronize the butterflies?

Did you make sure both fast idle and idle speed screws were out when you did it?
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Brian Vogel
Grand Master
Username: guyslp

Post Number: 373
Registered: 6-2009
Posted on Sunday, 19 May, 2013 - 11:22 pm:   Edit PostDelete PostView Post/Check IP

Paul,

No.

I still haven't figured out how one is supposed to "get the required visual" to do that task. Based on figure U33 I'm gathering one determines the position of the throttle butterflies based upon the tilt of the securing bolts of the throttle levers (item 11 in the figure) on each side.

Are there specific instructions related to doing this? I can't seem to find them and don't recall having seen them. They're probably buried somewhere in Chapter K, but if so I haven't seemed to notice them, and certainly don't recall seeing any instructions where both the fast idle screw and idle speed adjusting screw were both supposed to be removed (which is how I'm reading your use of "out") when you did something.

It's very frustrating simply trying to figure out even what order to attack things in. [Like this is news to anyone who's been reading this saga so far.]

Brian
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Paul Yorke
Grand Master
Username: paul_yorke

Post Number: 1020
Registered: 6-2006
Posted on Monday, 20 May, 2013 - 02:29 am:   Edit PostDelete PostView Post/Check IP

Brian, make sure No throttle stops are touching. idle and fast idle .

loosen the right hand front spindle clamp.
manually close the right butterfly. tighten clamp.

tighten clamp.

the spring should be closing the left butterfly. you are closing the right. both should be closed.

there must be some YouTube videos or articles somewhere.

without the basics you are p ing in the wind.

you might as well be driving around with a completely flat Tyre and asking if you need a prop shaft, wheel bearing, diff, or shock dampers?


trying to run before you can walk springs to mind .

:-( :-( :-(
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Brian Vogel
Grand Master
Username: guyslp

Post Number: 374
Registered: 6-2009
Posted on Monday, 20 May, 2013 - 02:49 am:   Edit PostDelete PostView Post/Check IP

Paul,

I truly appreciate the help, but when one is utterly ignorant on this, as I am, there are a lot of "false beliefs" and potential pitfalls. I don't consider it "running before I can walk" since I haven't actually tweaked anything, but brainstorming about the whole process. That's one reason I have been moving glacially slowly on this, in an effort to sort out what's what and in what order "the appropriate steps" should be taken.

No matter how much material is out there on each step, and I'm sure there is quite a bit, it's only from the voices of experience that I'm going to get some perspective on the probable "correct order" of approaching the various issues. I have received quite a bit of help here, and even within the cohort there have been widely divergent recommendations based upon the variety of past experiences being brought to the table. I have to sift through those, as well.

I'll be printing out your latest offering and taking it to the garage today.

Brian
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Geoff Wootton
Prolific User
Username: dounraey

Post Number: 177
Registered: 5-2012
Posted on Monday, 20 May, 2013 - 03:16 am:   Edit PostDelete PostView Post/Check IP

Hi Brian

I have to be careful commenting here as the carbs on my SY-I are very much simpler than those on the SY-II, but here's an observation - maybe Paul can correct me if I am drawing the wrong conclusion.

In your last photo but one, entitled Idle Adjusting Screw you show that the screw does not touch the metal stop. I am assuming the following 2 conditions are in effect:

1. The fast idle cam/choke is off.

2. The idle speed is around 600 rpm.

If this is the case, then your carbs are definitely miles out as regards synchronisation. The reason for this is one of the butterfly valves is acting as the throttle stop instead of the throttle stop screw. This means that one of the butterfly valves is fully closed. If the valves were synchronised then they would both be fully closed and hence you would not get an idle speed at all. Therefore the other valve must be partially open allowing you to get a rough idle at around 600 rpm. The bank that has the partially open butterfly valve is doing all the work.

Geoff
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Geoff Wootton
Prolific User
Username: dounraey

Post Number: 178
Registered: 5-2012
Posted on Monday, 20 May, 2013 - 03:53 am:   Edit PostDelete PostView Post/Check IP

Hi Brian

I understand your comments of false beliefs and potential pitfalls, but what Paul has outlined above, regards setting the butterfly valves is an absolute.

My suggestion is this is the very first check/adjustment you carry out on your carbs. If the butterfly valves are out, then there is no point in doing any other adjustment. It is the definite No 1 start point in tuning the carbs.

Geoff.
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Brian Vogel
Grand Master
Username: guyslp

Post Number: 375
Registered: 6-2009
Posted on Monday, 20 May, 2013 - 09:12 am:   Edit PostDelete PostView Post/Check IP

Geoff,

Condition 1 in your list was true but condition 2 was not. The laser tach was giving me readings between approximately 475 and 525 RPM.

For the sake of clarity, when you say "throttle stop screw" I presume you mean the idle stop screw, AKA the idle speed adjusting screw. In looking at the diagram I see there's a full throttle stop, but I presumed this simply stopped the travel of the linkage at its maximum point when the accelerator is pressed.

I forgot to take my camera today, so I don't have photos to post, but I took off the main air horn to take a look at what was going on with the choke butterfly and it seems to be fine. I gave it a spritz of carb/choke cleaner to make sure all was moving freely, but that didn't seem to change much.

In looking at the positions of the respective throttle butterflies they may be OK, but my next step is going to be following Paul's advice and setting instructions so that I know that they're synchronized. I think I'm going to have to acquire another idle stop/adjusting screw since the one in the car is so short. In SRH33576 the screw is much longer and has a hex head on it. Heaven only knows which of the two is the "correct" one at this point. All I know is that everything I've seen so far suggests that the current one won't allow for any functional adjustment.

Brian, who remains very grateful for all the help that's been offered to me throughout this adventure
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Paul Yorke
Grand Master
Username: paul_yorke

Post Number: 1021
Registered: 6-2006
Posted on Monday, 20 May, 2013 - 05:03 pm:   Edit PostDelete PostView Post/Check IP

Brian , both screws are correct.

I AM pretty sure that they are not a problem.

As Geoff says, the butterfly must already open or it would not be idling.

Of course you May have am air leak or the valves in the butterflies might be leaking or or or or or.

These carbs are great. The biggest problem they suffer from from is inexperienced human intervention.
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Brian Vogel
Grand Master
Username: guyslp

Post Number: 376
Registered: 6-2009
Posted on Tuesday, 21 May, 2013 - 12:33 am:   Edit PostDelete PostView Post/Check IP

Paul,

Now we're getting into confusion land, as I can't follow your antecedents.

What "both screws" are you referring to?

Geoff seemed to be referring to the throttle butterflies, saying that it's possible that one is open and the other is not (or one is appropriately open and the other is in a relatively closed position) and that this could cause the rough idle since, essentially, one carb would be providing the normal amount of fuel to its bank while the other would be providing none (or very little), causing a "siphon off" from the good side and causing problems . Or at least that's how I'm reading him. You refer to a single butterfly, which leaves me with one of three: choke butterfly (which I don't think you're talking about), or the throttle butterfly for either the A-bank or B-bank carb.

At this juncture since I know the carbs were rebuilt by a dealership that was (and is) definitely one of the "go to places" in the mid-Atlantic states I have no intention of touching them. What I had been planning was to follow-through with your suggestion regarding synchronizing the throttle butterflies after I've run the engine enough to warm things up and get the choke/fast idle to kick off.

What I thought was interesting the other day is that once the choke butterfly kicked off is that if I essentially manually put it partially back on by pushing down to close it part way that's when the engine would begin picking up idle speed and become very smooth almost instantly. It seems this should not be so if the throttle butterflies weren't synchronized since partially closing the choke butterfly doesn't cause any corresponding change in the positions of the throttle butterflies. But, it also causes enough change in air flow that if one throttle butterfly is "somewhat closed" relative to the the other that the change in air flow might cause it to be pulled open (even if minimally) or, perhaps, the overrun valve to have enough "push" occurring on it on the relatively closed butterfly that it opens.

Unless you, or someone else, tells me that there's a good reason, given additional information, not to try to synchronize the throttle butterflies as a first step at this point it seems like a good place to start.

The fact that I was able to get a good, solid, and smooth (if fast) idle just by that little temporary hand adjustment of the choke butterfly has actually given me a great deal of hope. I wouldn't have expected this if there were a huge number of other issues "out of whack."

Brian, who's going to have to move this car very soon [most likely by having it taken by flatbed to my home]
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Jeff Young
Prolific User
Username: jeyjey

Post Number: 147
Registered: 10-2010
Posted on Tuesday, 21 May, 2013 - 12:55 am:   Edit PostDelete PostView Post/Check IP

Hi Brian,

What I think Geoff was referring to is that if it's not sitting on the idle stop screw at idle, then something else is keeping it from rotating further to sit on the stop. It could be that the throttles are unbalanced and one is fully closed (and acting as a stop), or it could be bind in one of the linkages, or a stop on the pedal.

I do think balancing the throttles and resetting the idle stop is a good place to start. Then again, I'm far closer to your level of expertise than to Paul's, so take that with a grain of salt.

Cheers,
Jeff.
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Brian Vogel
Grand Master
Username: guyslp

Post Number: 377
Registered: 6-2009
Posted on Tuesday, 21 May, 2013 - 01:14 am:   Edit PostDelete PostView Post/Check IP

Jeff,

I'll check the linkage, but I think it very unlikely that it's not going through its full travel based on what I've seen/found thus far. A throttle butterfly could certainly be acting as a stop, though.

The length of the idle stop screws in my two cars is *very* different. It really makes me wonder if the one in LRK37110 is the correct one, but that remains to be determined later.

I plan on synchronizing the throttle butterflies first, then following the official procedure for setting the fast idle and idle stop screws and see where that gets me. At least these things are easily tweakable/reversible.

Brian
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Brian Vogel
Grand Master
Username: guyslp

Post Number: 381
Registered: 6-2009
Posted on Tuesday, 21 May, 2013 - 12:12 pm:   Edit PostDelete PostView Post/Check IP

Just as an FYI in the ongoing story. I did sync the butterflies today.

I really don't think I did anything, really, but wanted a definite baseline. It's most likely that the next pages in this story will be written on the Setting the Fast Idle thread.

Brian
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Jeff Young
Prolific User
Username: jeyjey

Post Number: 150
Registered: 10-2010
Posted on Tuesday, 21 May, 2013 - 06:35 pm:   Edit PostDelete PostView Post/Check IP

Hi Brian,

"I really don't think I did anything...."

That's OK. Remove each variable from the equation in turn, and when you're down to the last one you'll have your answer. ;)

Cheers,
Jeff.
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Jan Forrest
Grand Master
Username: got_one

Post Number: 476
Registered: 1-2008
Posted on Wednesday, 22 May, 2013 - 10:41 pm:   Edit PostDelete PostView Post/Check IP

When my Shadow 1 was running poorly at idle or not pulling well much as described above I went through all the carb checks as detailed with no improvement. On a hunch I started to remove the plug leads one at a time to see what results it gave. After a fair few goes - with a V8 there isn't much difference at idle from disabling one cylinder - I found the problem. Despite checking, rechecking and re-rechecking I'd got 2 leads transposed so that 2 cylinders weren't receiving the spark at the correct time. Dumb trick, I know, but these things are sent to try us ...

I used the same technique to confirm an imbalance between the carbs as there was a difference between the 2 end cylinders on one bank and the center 2 on the other. Not everyone realises that each carb feeds the cylinders like that so that if one completely fails in service the engine will continue to run as a V4. I've not noticed anything obvious in the workshop manual describing this feature.
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Geoff Wootton
Prolific User
Username: dounraey

Post Number: 185
Registered: 5-2012
Posted on Thursday, 23 May, 2013 - 01:48 am:   Edit PostDelete PostView Post/Check IP

Jan

I seem to recall something about this. Re: routing of the inlet manifold. I did a visual check but could not draw any conclusions. Has anyone any information on this?

Geoff

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