| Author | Message | ||
     Patrick McGlashan New User Username: pmac Post Number: 3 Registered: 06-2024 |
Hi everyone I have a rough idle issue with my 1977 SW II, LRF32027. I would greatly appreciate inputs from anyone as I'm at my wits end Whenever the engine is running and I remove, one at a time, the plug wire from A2, A3, B1 and B4, the engine does not stumble or runs rough(er). However, whenever I remove the plug wire, one at a time, from A1, A4, B2 and B3, the engine runs rougher. If I remove, say, A3 plug wire with the plug attached with the engine running, THE PLUG FIRES. I did a compression check on all 8 cylinders and they were all at 125 psi. The plug wires have been confirmed to be connected correctly according to the sequence on this forum With the timing mark on the crankshaft pulley set to TDC the Rotor is aligned with A1 plug wire. New plug wires were installed recently I have BPR4EVX plugs installed. They have less than 500 miles on them I installed a pair of dial indicators to the carby dashpots. According to the readings, A bank carburetor piston indicated 0 (zero) upward movement when the throttle lever is manipulated. B bank dial indicator shows vertical movement of the piston in the dashpot. A bank dial indicator reading was as steady as Ayers Rock IT APPEARS THAT NO FUEL IS GETTING INTO THE AFOREMENTIONED CYLINDERS The car has lots of power when driven. It's just that it runs rough and the idle is quite unstable as evidenced by the RPM on a timing light. According to the readings on the dial indicators, it appears A bank carby is not working. I can't believe that the car has so much power/acceleration on what appears to be running on four cylinders if I briefly put my hand near the tailpipe when the engine is running I can feel the rough idle it gets worse. I removed both carbys and sent them off to have the butterfly spindles replaced since one of them had a slight play. After I received the carbys, I replaced the jet and float in both units. I made sure that the heights of the floats were adjusted according to the shop manual, and confirmed that they moved freely After installing the carbys the same issues reappeared, Rough idle and evidence A bank carby is not working. I checked and or replaced all vacuum lines and pipes for leaks and found none. I checked the timing and it was adjusted to 15 degrees BTDC. SMOG equipped engine. I replaced a faulty EGR valve due to high Nox during a smog check. All other SMOG readings were well below normal. The new EGR valve appears to be working as advertised. Regards Patrick LRF32027 | ||
| Jeff Martin Frequent User Username: jeff_r_1 Post Number: 656 Registered: 07-2018 |
Weakener device is faulty on "A" Bank carb ? I don't have this car, but after reading countless posts about the problems that these cars have, it sounds like that maybe the problem _ something to check. There are solenoids in the system that can fail, and/or stick open or closed. Test by disconnecting the vacuum line to the top of the float bowl. This will take the weakener out of the equation. I haven't looked to see if your car has a weakener device on it, but the symptoms do point to it as being faulty. A car that acts up in this manor will run at speed because there's enough atmosphere and fuel flowing into the engine to over-come the problem. What it does is create a controlled vacuum leak so no fuel is getting into the engine on deceleration, and in that sense, it's also acting as a pollution control device. Others will chime in if I'm wrong. | ||
| Patrick McGlashan New User Username: pmac Post Number: 4 Registered: 06-2024 |
Jeff. Thanks for your input. The car has a Weakner Device setup. However, the vacuum lines from both carbs goes into the weakener and ends up inside a common chamber. Therefore, if the weaker device is the issue both carbs would "acting up" equally. Something is causing a lack of vacuum (depression) above the piston within the Dashpot. The piston needle is straight as a machinist ruler Before I had the rough idle issue, I followed the procedures in the shop manual to adjust the Venturi adjustment screw for the weaker device with a Manometer. It would not respond to any adjustments. I checked for vacuum leaks and found none. Patrick LRF32027 | ||
| Jeff Martin Frequent User Username: jeff_r_1 Post Number: 657 Registered: 07-2018 |
I can't help you much further with this, but humor me and pull the vacuum lines off of each carb that connect to the weakener and see if that doesn't solve the problem. SU carbs are not complicated things, it should not be that difficult to find out why the piston in that carb will not rise when its butterfly valve is opened. This may be a stupid question, but is the butterfly valve opening on the problem carb when the accelerator is depressed ? Perhaps the linkage to the carb is loose up near the carb and its valve isn't opening. | ||
| Larry Kavanagh Frequent User Username: shadow_11 Post Number: 849 Registered: 05-2016 |
This may sound like a stupid question but have you checked the small fuel filter on the A-Bank carb? | ||
| Patrick McGlashan New User Username: pmac Post Number: 5 Registered: 06-2024 |
Hi Jeff. Carbs are SU HIF7 Today I will do as you suggest. I will pull the vacuum lines off the carbs and see what happens. The small filters near the carbs were replaced with new ones a few days ago. they were both wet, which suggest the carbs are receiving fuel. Butterflys: the butterfly is firmly affixed to the spindle and moves freely. However, I noticed something peculiar. When the engine is running rough, I discovered that if I barely rotate the choke lever---this would be the lever that has the adjusting screw as such that during cold starts the tip of the adjusting screw rides on top of the choke mechanism Cam to raise the rpm during choking. If I barely rotate the lever clockwise, away from the cam, the roughness goes away. If I rotate it counterclockwise the rough idle returns immediately. Furthermore, when I rev up the engine using one hand to manipulate the throttle linkage and the other hand to manually rotate the choke adjusting lever clockwise the A bank carb dial gage indicated movement of the piston similar to the movement of the piston in B bank carb. As soon as I release the choke lever and continue to rev the engine with my other hand, the A bank dial indicator indicates no movement of the piston in the dashpot. To me it appears the issue of A bank piston not rising is somehow related to the choke mechanism By the way. I lucked out and stumbled upon a pair of SU HIF7 carbs on eBay a few days ago. They were still connected to the central adaptor with the throttle mechanism still in place. They were listed for USD $100 with a Or Best Offer option. I didn't bother to haggle so I bought them with the buy it now option. The pictures for the listing appears to show that the linkages were not disturbed. Upon receipt of the carbs I will study the setup and compare it with mine, especially the placement of the levers on the spindles etc. I will report back to the forum when I get the issue sorted out. In the meantime if there's a SU HIF7 expert out there I'm soliciting your help Patrick LRF32027 | ||
| Jeff Martin Frequent User Username: jeff_r_1 Post Number: 658 Registered: 07-2018 |
Don't start messing around with the choke, that's not the problem, you have a vacuum leak on the carb where the piston doesn't rise at idle. What you're doing when you close the choke off a bit is over coming the vacuum leak and in turn, the piston rises _ that's all. It's not a big vacuum leak because when you drive it down the road, there's enough air flowing into the engine to over come it, and the car drives fine. Don't get into the rut of "maybe it's this or I haven't tried that" routine, trouble shooting is not a guessing game. Are there heat isolators between the carbs and the intake manifold or anywhere on the intake manifold ? They can be made from bakelite or a fibre material. They act to protect the carbs from heat soak on hot days, they can develop hair line cracks that can't be seen, until things are bolted tight. | ||
| Jeff Martin Frequent User Username: jeff_r_1 Post Number: 659 Registered: 07-2018 |
Also ? Did this problem start on its own, or were you adjusting things and you brought the problem upon yourself ? | ||
| Robert J. Sprauer Frequent User Username: wraithman Post Number: 854 Registered: 11-2017 |
Smoke test time. Good excuse to light up a nice stogie and see if the engine pulls in any. A cheap test to do. | ||
| Patrick McGlashan New User Username: pmac Post Number: 6 Registered: 06-2024 |
Jeff Thanks for the inputs. please keep them coming Heat isolators are installed between the carbs and the intake. I will check the problem carb one for cracks. The rough idle problem has been there for a long time Wraithman, good to hear from you. It will be a waste of a good stogie. The air from the fan would blow the smoke from here to Timbuktu I did a drop test with the piston in the dashpot. After taping close the two holes in the piston, the piston sank rather quickly. furthermore, the piston has a noticeable play/wobble when inserted into the dashpot. Also of note, I just received a pair of used HIF7 carbs I bought off eBay. I did the same test with one of the carb and I noticed that the piston fitted in the dashpot very snugly as if it just arrived from the factory. Also, the drop test took approximately five seconds to complete the journey. That preliminary test indicates the eBay carbs are in better shape than the A bank carb that's on the car As an aside, the eBay carbs appears to have been "idle" for many years. Lots of varnish on the float, which happens to be in very good condition. As for the jet and mixture and pickup tube, they were frozen in place. Overall a good cleaning up and a rebuild kit ought to revive the carbs for continued service. It appears that if the piston has a significant wobble and a rapid drop test then, the vacuum signal above the piston will have very little effect on raising the piston when the engine is running. It's akin to a vacuum leak, correct? Regards Patrick LRF32027 | ||
| Jeff Martin Frequent User Username: jeff_r_1 Post Number: 660 Registered: 07-2018 |
A piston with significant wobble in the dash pot, would indicate that there's some mechanical failure going on. It should be pretty easy to compare the carbs from eBay to your problem one and figure it out. Each piston is machined to it's own dash-pot, maybe someone was buggering around with yours and now you're dealing with that problem. It would be nice for someone to take a video of this "wobble". You up load the video to you-tube and then you post the link to that video here. The space between the piston and the dash-pot body is with in 10,000ths of an inch. For reference, a human hair is a round 4 thousandths thick or 40,000ths thick. | ||
| John Rowney Experienced User Username: johnrowney Post Number: 173 Registered: 02-2015 |
It might be worthwhile trying a simple test for a leaking inlet manifold gasket. Squirt carburettor cleaner around the manifold areas when idling. If the idling becomes smoother and revs increase, it will be a good indication of a leaky gasket. See my old post "Removing the needle seat from a Solex 4A1 carburettor". You can find it with the last post on 22 June 2020. Once in the post, scroll down to 4 April 2020 and the discussion of the detection and repair of the manifold leak unfolds from then on. | ||
| Alan Dibley Frequent User Username: alsdibley Post Number: 402 Registered: 10-2009 |
Patrick, the dashpot wobble is an indication that someone has mixed up the dashpot/piston pairing. At some time in the past a piston has been fitted from a different carb. In many years experience of SUs I have never seen anything but zero slop - the piston never(???) wears. If the two carbs have been removed with the pairing not noted one will probably jam, and a "spare" one fitted. The units are matched during manufacture and must not be switched. That carb will never be OK (unless you can find the original piston - or a very good fit). Check the two "new" ones you have and use one of them. Alan D. | ||
| Mark Aldridge Frequent User Username: mark_aldridge Post Number: 873 Registered: 10-2008 |
Patrick, I would be concerned about the loose carb piston, this is not correct. However I had an early Spirit and had difficulty achieving carb balance ( same as Shadow2 I think). I had to balance the carbs at 2000 rpm, then set up the linkage to hold this balance and then retrim the balance at tickover with the idle screws.Very fiddly, but the car ran well afterwards. I have used the same principal on my Shadow1 and many others. It adjusts out imbalance caused by wear at speeds above idle. Mark | ||
| Patrick Lockyer. Grand Master Username: pat_lockyer Post Number: 2592 Registered: 09-2004 |
Are the stove pipes in good working order? Inverted test with piston transfer holes plugged with 47.6 mm carbs seven to eight seconds would be better imo. Interesting with a scope using the firing plug voltage trace for all cylinders ref A and B bank. | ||
| Patrick McGlashan New User Username: pmac Post Number: 7 Registered: 06-2024 |
Gentlemen. PROBLEMS SOLVED I installed one of the "new" eBay carb after thoroughly cleaning it up and used compressed air to clear out the passages. I also transferred all the new bits from the errant carb to the ebay carb. The drop test was nine seconds Hello!! the engine started up and ran a lot better than before. It still had a slight miss, however, even though I had thoroughly operationally checked the EGR valve...used a vacuum pump to confirm the soundness of the diaphragm, movement of the shaft as the rpm was increased, WOT closure of the valve, I went ahead and disconnected the vacuum hose from the valve and plugged it. The rough idle immediately ceased and the engine is now purring like it just rolled off the assembly line. As for the EGR valve. If the coolant temperature sensing bulb is faulty, would it affect the operation of the EGR solenoid as such that the solenoid remains open all the time? I partially tested the solenoid by disconnecting the vacuum hose to it. I then connected a short piece of hose directly onto the valve and blew into it. I was able to blow air through the valve. I couldn't do a "no air going thru" test because the coolant temperature was way above either 54F or 57F Also, I tested the EGR solenoid temperature bulb located at the thermostat housing. According to the shop manual, if the temperature is above 57F and a test light is connected across the lucar connectors, the test light should NOT come on. The test light came on. Considering the test result, does this means the EGR solenoid "thinks" that the coolant (engine) is cold and stays open causing an uninterrupted vacuum signal to the EGR valve?? I would like to thank everyone so kindly. I couldn't have done it without your help. I spent the past three weeks trying to sort out the rough idle issue to no avail. It was very frustrating to stand there looking at the engine and don't know what else to do. Regards Patrick LRF32027 | ||
| Randy Roberson Frequent User Username: wascator Post Number: 895 Registered: 05-2009 |
Great posts! My ‘77 USA Wraith II has the same issue. I have the carbs off now, looking for the problem; the “root cause” as we used to say at work. I tried disconnecting the weakener system and no change. My car has the phenolic blocks at each carb and where the tee contacts the intake manifold. |
