| Author | Message | ||
     Daniel Shepherd New User Username: 1957_grey_cloud Post Number: 46 Registered: 12-2021 |
We just had our twin SU's reconditioned by a company of excellent repute, and our local RR mechanic has fitted them. But for the life of us we can't get the beast to idle under 1000 RPM, the idle screw is at minimum and the automatic choke disconnected. Grateful for any insights, we are so close to getting it back on to the road now... | ||
| Jeff Martin Frequent User Username: jeff_r_1 Post Number: 561 Registered: 07-2018 |
This assumes that the 57 has the V8. https://youtu.be/3ih5h1J-AN4?si=eoQ4rkgWIhmgIZ7b | ||
| Daniel Shepherd New User Username: 1957_grey_cloud Post Number: 47 Registered: 12-2021 |
Thanks Jeff - ours has the inline six,so I'm not sure if the carbs are similar, but I will watch. I'm wondering if there's a vacuum leak somewhere - but we have only just had them reconditioned at considerable expense... I think the mechanic is ready to pour petrol on the thing and be done with it! | ||
| David Hughes Experienced User Username: wedcar Post Number: 151 Registered: 07-2004 |
Daniel. The carburetter setting on these cars is quite involved, however is well explained in the workshop manual but takes some time to get them right. If you have followed all the steps mentioned in the manual, likely suspects could be: 1. the fast idle cam is still in operation. 2. The butterfly by-pass screw is still open too far. Even when carburettors are overhauled, it is good practice to: 1. ensure the piston and needle assembly drop fully on to the jet bridge. 2. Ensure The float level in the bowl is correct by removing the piston housing with piston and needle (being careful not to damage the needle), switch on ignition, fuel pump running, look down the jet hole and ensure the fuel level is about 1/16 inch below the top of the jet. Trust this helps. Regards David | ||
| Daniel Shepherd New User Username: 1957_grey_cloud Post Number: 48 Registered: 12-2021 |
Thanks David - the mechanic has just informed me that the dashpot had not been refilled with oil by the reconditioner, even though the damper cap had been screwed on pretty tight. The mechanic is going to have another crack this week - fingers-crossed and I'll be sure to report back. If successful then there's an exhaust leak that needs to be fixed, and then we off for a Warrant of Fitness check... | ||
| Jeff Martin Frequent User Username: jeff_r_1 Post Number: 565 Registered: 07-2018 |
Daniel I don't think the missing oil in the damper tubes is your problem. The oil is to control the movement of the pistons upon take off or hard acceleration, it should not effect the idle. With no oil in there, if you do a jack rabbit start you will get a puff of black smoke and some possible hesitation because of the big gulp of fuel the engine gets from the pistons rising too quick. Another thing to check is to make sure that the seats of the by-pass screws have not been damaged form over tightening, there should be no grooves in them. A possible vacuum leak may be at either end of the intake manifold, there may be ports there, I know there is on my Mark VI to run the windshield washer, but I don't know if RR did away with that on Cloud 1"s or the Bentley S 1's Check that the gaskets are installed correctly where the carbs bolt up to the intake manifold. . | ||
| Daniel Shepherd New User Username: 1957_grey_cloud Post Number: 49 Registered: 12-2021 |
Thanks Jeff, I have not heard from the mechanic so perhaps bad news is coming :-( Interesting point re: the windshield washers. Yes, our Cloud 1 has this system, but when we obtained the car from our Uncle's estate the windshield washer bottle was absent. I am now wondering if this could have some unintended consequences. I had actually asked the mechanic if we should not remove them and put plugs in the inlet manifold. Daniel | ||
| Jeff Martin Frequent User Username: jeff_r_1 Post Number: 569 Registered: 07-2018 |
If you still have the original rubber vacuum line connected to the manifold, then they need to be disconnected at the manifold and blocked off there. If there is indeed a vacuum leak from the old lines or if they've become disconnected inside the car causing a leak, then that will certainly cause a problem. Furthermore if the carbs have been tuned with a vacuum leak, that will have to be dealt with as well. It's the only vacuum port that was needed, and that was to run the windshield washer, unless there is a vacuum gauge installed. Maybe in the Clouds RR used some vacuum operated switches for ducting that I'm not aware of. If that's the case and there is a vacuum leak in such a system, then you can always block the port(s) off temporarily to see if that cures you idle problem. It was common that the glass water bottle was missing, they very often broke if parked outside in freezing weather with water left in them. They also broke when cold fluid was added in a hot engine bay. Cars were driven on a cold fall day and the driver needed to fill the bottle, he stops at a gas station where the fluid is kept outside and sometimes, not brought in from being left outside over night. You can guess what happens. | ||
| Daniel Shepherd New User Username: 1957_grey_cloud Post Number: 50 Registered: 12-2021 |
Reporting back on this issue. We have taken the window washing circuit out the equation, still no joy. After Jeff Martin's comments above, I have no inclination to recommission this system! I have a clearer idea of the problem, and hope that someone may have successfully wrestled with it in the past: Here is what is happening: 1) With the engine off, the throttle lever (on he right carb) moves easily and returns promptly to the idle position when released. This is good. 2) When the engine is running it does not, and the throttle lever puts up substantial resistance compared to when the engine is off. Subsequently the engine is "idling" at about 500 RPM too high. Maybe something is stopping the two butterflies from closing fully? It is strange. All help appreciated - this is our last challenge before getting the beast to the warrant-of-fitness station! | ||
| David Hughes Experienced User Username: wedcar Post Number: 157 Registered: 07-2004 |
Daniel With the two carburettors separated by disconnecting the linkage, engine at running temperature and stopped, are the spindles easy to move by hand, if not, it is likely that when the carbs were overhauled, if new bushes and spindles were fitted, they have been fitted with not enough clearance. Also possible that the throttle butterfly is not central in the bore. The carbs would best be removed to rectify this. Regards David | ||
| Daniel Shepherd Experienced User Username: 1957_grey_cloud Post Number: 51 Registered: 12-2021 |
Cheers David, With the engine off the spindles are incredibly easy to move. When the engine is running, they become very stiff and don't seem to want to travel all the way to the idle position. I will talk to the mechanic on Monday - I am sure he will be overjoyed with thought of removing the carbs again! Thanks for you advice Daniel | ||
| Daniel Shepherd Experienced User Username: 1957_grey_cloud Post Number: 53 Registered: 12-2021 |
Thanks David, the mechanic is resigned to removing the carbs, which for an engine bay with so much room, is really a trying task :-( His opinion is that the vacuum is too strong in the manifold, and that this is holding the butterflies open and preventing the car returning to idle. But I will suggest he checks the clearances etc as you directed, another option is poppet values, which can be bought for SU carbs. Such lovely pieces of eye candy, but at this point in time a bit vacuous!! Daniel  | ||
| Jeff Martin Frequent User Username: jeff_r_1 Post Number: 586 Registered: 07-2018 |
Danial, what are "poppet values" or did you mean poppet valves, and if you meant to say valves, what are poppet valves ? Logic would suggest a question, if the vacuum of the engine is holding the valves open, what does the mechanic hope to accomplish by removing the carbs.? What does he expect to find that can be corrected ? If he creates more clearance in the shafts, this will create a vacuum leak there, and if he does create more clearance, won't that cause the butterfly valves to bind. I would suggest this. Remove both dash pots so that ones fingers can get in there to hold both valves shut, this will centre the shafts on each carb. Have an assistant install the connection between the carbs while they are being held shut, check to see that there is no binding happening between each carburetor with the linkage connected. If the vacuum is still holding the valves open, a stronger return spring may be needed, but if it was running before with the original return spring _ well that's the part that needs solving. Another question, was care taken to properly seat the butterfly valves in the throat of each carburetor when the new ones were installed ? How badly were the old valves worn into the throat of the carb, were the bushing installed properly ? Normally just the shafts wear, and that's all takes to rebuild this area, the aluminum wears on the brass, or even steel See video. https://www.youtube.com/watch?app=desktop&v=Yeu-t9ojtBc | ||
| David Gore Moderator Username: david_gore Post Number: 4245 Registered: 04-2003 |
Jeff, All you need to know about poppet valves: https://en.wikipedia.org/wiki/Poppet_valve . | ||
| Jeff Martin Frequent User Username: jeff_r_1 Post Number: 587 Registered: 07-2018 |
 If this is what you're talking about David, I don't understand how this is going to help. As soon as enough vacuum tugs on the valve, isn't a bit of fuel just going to flow into the engine, and cause the same result of a high idle ? I've seen a few carbs on our cars with the straight six, HD4, HD6 and HD8, I've never seen this. On my MK VI, there is an air-bleed at the bottom of the jet where the fuel flows in from the float chamber, doesn't that do the same thing ? "The Weakener Device" to keep the car from popping back when the butterfly valves are fully closed on deceleration. If Danial is running HD8 SU's, maybe the idle screws need to be turned out 3 turns on both carbs then tuned. The idle screws turned out that much should be enough to keep the butterfly valve from opening at idle. Assuming that the idle screws are there. Would it not also keep the carb valves from opening under high vacuum at idle ? EDIT: The idle screws are there, I can see one of them on the left carb. (actually they look like a set of HD6's) | ||
| Daniel Shepherd Experienced User Username: 1957_grey_cloud Post Number: 54 Registered: 12-2021 |
Thanks Jeff and David, it might have been a tongue-in-cheek comment from the mechanic! It was my bad calling it a poppet value, I got the wrong end of the stick on the internet, what I meant was an overrun limiting valve. To me this would be conceptually the same as putting a grommet into an eardrum, but an ear drum is a lot simpler than a carburetor! I think the mechanic, having been quite thorough, suspects the throttle butterflies are to blame, hence wanting to remove the carburetors and do another rebuild. The fellow who restored the carbs came and had a look last week, he is very experienced and he had no ideas other than to put a stronger spring. This of course has consequences up stream by stiffening the accelerator peddle. I will send your suggestions to the mechanic. I am feeling very frustrated over this as I want the car for my wedding day in February, and what I thought was going to take a week has already taken over two months. The fact that I'm about as mechanical as a lump of coal doesn't help matters! If I could I'd just buy a new set - there seems no light at the end of tunnel here :-( Thanks again for your thoughts on the matter Daniel | ||
| Jeff Martin Frequent User Username: jeff_r_1 Post Number: 589 Registered: 07-2018 |
If he takes the carbs. off, which sound like he's going to, hold each carb, one at a time up to the light on the air cleaner side _ he should be looking through the the intake manifold side. He should see a nice even line of light around the circumference of the butterfly valve if it's seated properly when held shut. In theory, there should be no light getting through, but the seal on the valve against the throat of the carburetor is never perfect, so the best that one can hope for is a thin even line of light, if it's dark in some areas and too much light getting through, then it's not "seated" properly. AND by February !!? The bloody thing should be running properly in an afternoon, certainly not more then a weekend. A carburetor is like sticks and stones compared to the human ear. How was it running before this so-called rebuild of the carbs ? What made you want to rebuild them ? From experience with other peoples carb rebuilds and why it won't run properly, it's because it was not assembled correctly, and/or it's out of adjustment. Sometimes parts are missing or all three. The HD6's are a little small for the 4.9 litre 6, so there is tremendous vacuum at the valves. A buddy of mine installed a 4.9 in his Wraith and it had HD8's. If it was running before with the factory return spring, logic tells you that adding a stronger return spring is not the answer, although it may solve the problem, it will create unnecessary wear on the butterfly valve shafts. At this point I'm going to say that the butterfly valves are not installed properly and the engines vacuum has nothing to do with it. Although atmospheric vacuum tugging on a valve that's not properly seated will cause problems. | ||
| NormanGeeson Unregistered guest Posted From: 81.99.74.184 |
Daniel There are several causes that result in the fast idle problem you are experiencing. I have provided some that very often trap mechanics. 1. Between December 1955 and late 1957 the company made many modifications to the throttle linkage. None of these were unfortunately issued as bulletins. One issue in particular was caused by the elimination of the “on stop” which allowed the linkage to over travel and resulted in the linkage “skidding”, in short destroying linkage synchronisation. 2. The following fault also affects all EPW chassis that are fitted with automatic transmissions and the engine will not return to idle when the engine is run. In this instance the installer has not allowed sufficient end float of the throttle shaft that passes through the bell housing. The alloy bell housing expands some 0.017 inch across when the engine is hot and needs at least 0.015 inch end float for even light running if the throttle shaft is not to be grabbed by the bell housing. The workshop manuals suggest this clearance is set at 0.010 inch which is insufficient. First hand I can tell you that if you drive a car in this condition the experience will be remembered for a life time. 3. The end float problem mentioned above can be repeated in the linkage between the carburetters, as the carburetter position’s move apart quite quickly when the engine runs. Adequate end float allowance must be present to prevent hanging up of the throttle butterfly discs. A situation can also occur where the linkage does not have enough clearance to allow for engine movement. 4. This situation is not so common except when the carbs have been rebuilt. This is when both butterfly discs have been fitted back to front, or behold when only one is wrong! I have a feeling that the carburetter shafts work in reverse on this engine (I remain to be corrected on that point) If the butterfly discs are fitted wrongly, they will not seat and idle is impossible. 5. Some unusual problems can occur when the carbs have been tuned with restricted breathing. In this instance the float chamber breathing has usually been compromised because each carburetter has not been fitted with TWO serrated fibre washers part number SU 1928. In the case of SI series 4.9 ltr engines these are listed, but not illustrated in the parts lists even by October 1958. Earlier engines have descriptions and listings, and mechanics are often mislead as they fail to realize that the quantities appertain to each carburetter 6. If memory serves me correct, around 1957 the idling screw ports were fitted with rubber seals on which the screws seated, this modification prevented by pass air leakage and erratic idling. Probably worth checking if you need to try “O” ring seals. I would suggest that you obtain two identical length pencils, unscrew that dash pot caps and place a pencil in each dash pot. Run the engine at idle and see if one pencil rises more that the other. This might point out if the problem is on one carb or both. (Message approved by david_gore) | ||
| Daniel Shepherd Experienced User Username: 1957_grey_cloud Post Number: 55 Registered: 12-2021 |
Well, we're back on the road now, albeit on the back of a truck! Thanks for all the help. After trying everything the carburetors were removed and sent back to the re-conditioner. My understanding is that he flipped the throttle butterflies around (as per Norman's #4 above) and had a general fossick. The mechanic then added an extra return spring. Outcome, the car now starts! Releasing the accelerator sadly does not return the car to its optimal idle position (circa 500 RPMs I am told). This can be done by sneaking your foot behind the pedal and pushing it up! Am I an optimist in thinking that after some use this issue will simply right itself!??!!? Over the Christmas break I will attend to all of the electrics (indicators, lights etc) and brakes, which on a short test drive yesterday seemed quite decent. Many thanks for the help, I have ten weeks to get the car road legal before my wedding :-) Have a great Xmas break Daniel  |
