| Author | Message | |||
     Dave Burbidge Experienced User Username: ovation Post Number: 25 Registered: 8-2009 |
Dear All, I have very frustrating problem. We have 1982 Spur and a 1982 Mulsanne. Both with the same engines. The Spur is well tuned and good on fuel( Jackie's car of course). The Bentley ( mine)has black fouled spark plugs and a blacker thicker deposit in the tailpipe.I had the SU's tuned but some but still not much improvement. The weakening system solenoid and anti run on solenoid wiring had been messed with by the previous owner and was disconnected when I bought the car. I think I have reconnected correctly but still I get a very black exhaust. Is there something obvious I am missing ?  | |||
| Jan Forrest Prolific User Username: got_one Post Number: 236 Registered: 1-2008 |
Have you checked for: Stuck choke? Blocked air filter? Worn or stuck float valve(s)? Incorrect plugs or plug gaps? Worn distributor cap? Tired plug leads? Any of these things and more can result in over an over rich mixture. Despite all the 'belt & braces' additions that Crewe placed in the fuel path and ignition circuit both systems are just basic post war technology - albeit the best available at the time that was fully proven to be as reliable as possible. | |||
| Bill Coburn Moderator Username: bill_coburn Post Number: 1313 Registered: 4-2003 |
Dave / I will put my money on leaking floats. They are made of plastic and leak at rupture points mounts etc. I picked up mine by accident. When stopped on a steep driveway nose down and idling I happened to notice a steady trickle of fuel from the escape lin at the left front of the engine. More later must go out! | |||
| Bill Coburn Moderator Username: bill_coburn Post Number: 1314 Registered: 4-2003 |
I'm back. This is a very common problem and what is more annoying is that even new ones occasionally leak. When they take on fuel they become heavier so the fuel in the bowl has to rise further before the flow is stopped. One other problem is that people have installed new floats and not set the level. This is detailed in the manual. Getting them out involves disconnecting all the bits and pieces, undoing the centre bolt in the manifolds and lifting the whole unit off. Turned upside down you can then remove the covers of the float chambers unscrew the float fulcrum and lift out the float. The level is set by bending a small arm on the float. As to the two solenoids, the running on one should be replaced as it has presumably stuck open which makes the engine impossible to run. Read all this in the manual which is availablke in the library ! | |||
| Jan Forrest Prolific User Username: got_one Post Number: 238 Registered: 1-2008 |
From a cold start the A bank carb on SRH24518 will leak a little fuel from the top of the float chamber until the engine settles down to a steady idle of 650rpm. After that it will stay dry all day, so I've left it alone until it becomes more of a problem. Incidentally she nearly failed the last MOT due to a 'low tickover' when the testing computer detected that the idle level was "under 850rpm". It was only due my insistance (including a few choice words that are rarely found in most dictionaries) that the idle was correct that the tester eventually allowed it. | |||
| Paul Yorke Grand Master Username: paul_yorke Post Number: 779 Registered: 6-2006 |
If the anti-diesel valve is disconnected and the engine will still run, it means that the weakener system must have also been not working other wise the engine would stop. If the weakener system is not working, then it will use more fuel etc. If you block the weakener air filter, does the engine cut out now? | |||
| Dave Burbidge Experienced User Username: ovation Post Number: 26 Registered: 8-2009 |
Hi Paul I blocked the air intake for the weakener and the engine keeps running although I can hear three clicks followed by a louder click from the choke assembly after few seconds after blocking the air intake.I put power into the solenoid and it does operate but whether its operating correctly is another matter. | |||
| Paul Yorke Grand Master Username: paul_yorke Post Number: 786 Registered: 6-2006 |
Hi Dave, That sounds as though something is wrong. It should cut out immediately the weakened filter is blocked. Check that all the hoses and wires are connected the same as the spur. No hoses off. Valves wired correctly etc. One valve should close on ignition (front) The other should open (I think) when cold. Compare with the Spur though. | |||
| Dave Burbidge Experienced User Username: ovation Post Number: 27 Registered: 8-2009 |
Thanks Paul I had a feeling that was the problem. I checked with the Spur and all seems the same but I will double check. | |||
| Dave Burbidge Experienced User Username: ovation Post Number: 28 Registered: 8-2009 |
Just checked the wiring. I can get the solenoid to click when I turn on the ignition.If I connect a 12 volt lamp accross the wiring I get a dim light. But no air seems to be coming in through the weakener intake. I removed the needle adjuster and nothing coming in there either. | |||
| Dave Burbidge Experienced User Username: ovation Post Number: 29 Registered: 8-2009 |
Finally  all wiring seems the same as the Spur. When I block off the weakener air intake nothing changes.What next ? Good reason to have two cars !!!! | |||
| Paul Yorke Grand Master Username: paul_yorke Post Number: 787 Registered: 6-2006 |
Hoses all on? (to both float chambers) Does it use the same vacuum for the intake blend flap. Speed control. Distributor advance. Check the one way valve and hose running down the front of B bank head. | |||
| Dave Burbidge Experienced User Username: ovation Post Number: 30 Registered: 8-2009 |
I checked the hoses and the distributor advance bellows is obviously leaking as I can suck and blow easily. On the Rolls you can hear the bellows working.So no advance control. Is that what cuts out the engine when you block the air intake? | |||
| Paul Yorke Grand Master Username: paul_yorke Post Number: 788 Registered: 6-2006 |
Hi Dave, Has your car got EGR equipment? A regulated vacuum is applied to the air space above the fuel in the carburettor. When the engine is cold it is not applied. Rear valve. When the ignition is cut, the front valve shuts and the air flow from the filter through the regulator (adjuster) to the carbs is blocked. This applies a much stronger vacuum which effectively sucks the fuel out of the jets and kills the engine. When the engine is hot and running the regulated vacuum above the fuel works against gravity and suction to lower the amount of fuel going through the jets. Weakening it. If the vacuum is not there to weaken it will be slightly rich when running. If the vacuum capsule is not working , the timing will be wrong and will also use more fuel.
OK, for some reason it wants to give the file an .ukn name. Download and save it. Change the .UKN to .PDF (Message edited by paul_yorke on 05 September 2011) | |||
| Paul Yorke Grand Master Username: paul_yorke Post Number: 789 Registered: 6-2006 |
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| Dave Burbidge Experienced User Username: ovation Post Number: 31 Registered: 8-2009 |
Continuing saga. I checked all the hoses , a couple were disconnected, and wiring checked and seems ok . I replaced the O rings in the weakener unit . They were all shot and I replaced some old brittle vacuum hoses. Now at least I have strong vacuum when there wasnt any before.Despite all this when I block off the weakener air intake the engine keeps going. Tomorrow we are replacing the distributor and coil with brand new one. It will help with the advance mechanism . And Paul there isnt an EGR on our cars.  | |||
| Bill Coburn Moderator Username: bill_coburn Post Number: 1315 Registered: 4-2003 |
Can I enquire as to whether you have checked the float levels????? | |||
| Paul Yorke Grand Master Username: paul_yorke Post Number: 790 Registered: 6-2006 |
Dave, Did you also check the one way valve at the bottom of the engine. Should allow outwards flow but not inwards. | |||
| Dave Burbidge Experienced User Username: ovation Post Number: 32 Registered: 8-2009 |
Congratulations we have a win!!! The one way valve was clearly not needed by the previous owner since the hose that is supposed to connect it was about 200mm short!!!the valve was sitting in space. For good measure I checked the floats thanks Bill and all is OK there. Now the whole thing works fine. The new distributor and coil courtesy of RA Chapman is great piece of kit . Well we are off to do a wedding today and will hopefully use a lot less fuel. | |||
| Paul Yorke Grand Master Username: paul_yorke Post Number: 794 Registered: 6-2006 |
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| Brian Vogel Experienced User Username: guyslp Post Number: 27 Registered: 6-2009 |
Dave, Having gone through a similar saga on my Shadow II this thread caught my attention. Might I ask what you're referring to by the "one-way valve"? For some reason this isn't pulling up an image in my head, while the anti-run-on and weakener solenoid valves instantly do. Congrats on having solved this nagging issue! Report back on what has actually occurred with your fuel consumption. Brian | |||
| Chris Browne Frequent User Username: chrisb Post Number: 57 Registered: 2-2010 |
Hello Brian, I think the object being referred to is the one in the photo.  It is close to the oil pressure sender and oil filter housing. Hope this helps. Kind regards, Chris | |||
| Brian Vogel Experienced User Username: guyslp Post Number: 28 Registered: 6-2009 |
Chris,  [For those that think I'm nuts for posting this in the wrong orientation, the forums would not let me post it otherwise. The image is 424x640 pixels in portrait orientation. The forums software apparently cares that 640x480 is with the 640 as the first dimension and 480 as the second.] That's the float chamber drain valve. I guess I'd never thought about that as being a one-way valve, but it must be so that vacuum is maintained after any overflow drains out. The last thing in the world I would have though about in terms of excessive fuel usage would be the float chamber drain valve being disconnected. My fun with this system was terrible engine run-on when the ground/earth for the anti-run-on solenoid "disappeared" somehow. Most disconcerting. Brian | |||
| Dave Burbidge Experienced User Username: ovation Post Number: 34 Registered: 8-2009 |
Yes, who would have thought that valve was so critical.The one way valve if disconnected means there is no vacuum and the weakener doesnt work. We ran the car over 150km yesterday for a wedding and she performs beautifully. I have found though, that most of the vacuum hoses and also seals in the weakener were all rock hard and brittle and leaking and the distributor bellows were leaking. Good result replacing them all for under $20 ( not including the new distributor) | |||
| Roderick Waite New User Username: rodwaite Post Number: 5 Registered: 1-2012 |
Hello Dave and all, just read of your problem for which your solution is interesting, and one to remember! I'm having troubles with my 1984 Spirit, that wouldn't idle and was incredibly hard to start. In my case I disconnected the weakener cut-off solenoid and blanked off the hose to solve the problem - but I notice the rubber hose connections are hardened with age, cracking and not sealing on the metal tubing. I'm awaiting new hoses now - I, too, would never have suspected the petrol drain valve of compromising the vacuum in the system! It's absolutely vital that the vacuum be maintained, and there are so many points at which it can be destroyed! Rod | |||
| Dave Burbidge Experienced User Username: ovation Post Number: 42 Registered: 8-2009 |
Rod I thoroughly cleaned the weakener and replaced all the O rings with new modern material ones , all the hoses, replaced the fuel filter. I replaced ( through a local specialist) the distributor with a new one from RA Chapman. Then I had the carbs tuned by my specialist who only charges a few dollars but he has a good ear and does it all the time !!! I also found a a problem in the weakener wiring when a previous owner had played around with the wiring and put it back together wrong. Car now runs like a dream . I have now replaced the distributor on my Spur and that makes a big difference. Anyhow both cars run really well. | |||
| Roderick Waite New User Username: rodwaite Post Number: 8 Registered: 1-2012 |
Good evening from freezing France. I'm intrigued by the weakener device. In the diagram posted by Brian Vogel (above) - which I think is the same as that in the Workshop Manual - can anyone tell me what the hose labelled 'A' is and does, and where it goes? It's the one from the top of the weakener on the left hand (fuel receiver) side. On my '84 Spirit it vanishes under the engine somewhere. It may or may not have any bearing on my less-than-perfect idling problem. Dave, I think every owner has a fiddle with the weakener, which does seem the primary source of a lot of problems! Thanks Rod | |||
| Jeff Young Frequent User Username: jeyjey Post Number: 65 Registered: 10-2010 |
I believe that's the hot-soak float-chamber vent (which vents excess pressure in the float chambers, such as after shut-off on a hot day). I think it's the open-ended hose right next to the float-chamber-overflow-valve in Chris Browne's picture above. Jeff. |
Shadow II Emmision Manuals TSD4200_3.pdf