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Post by markymark on Jun 24, 2015 21:12:57 GMT
Hi Guys, I took my P5B for its MOT and the inspector commented on the smell and how rich it must be running. Full of enthusiasm (with a new MOT cert) I went home and opened the bonnet. First thing I saw was that there was petrol seeping from the union at the bottom of the float bowl on one carb that carried petrol to the jet. So I took the carbs off, stripped them and cleaned them and fitted new main jets. I then put them back on with new gaskets and refilled the dash pots. The car started no problems but needed tuning. I bought a colourtune that seemed to work well. I then balanced the carbs with an airflow meter and set up the throttle link per the manual. The result was a car that seemed to run better than ever before. Tick over nice and smooth etc.
The first hint of a problem emerged after driving for twenty minutes or so. She started to lose power at the top end and then reduced to a crawl. I pulled over and she settled into a tick over whilst I checked what I could under the bonnet. I get back in the car and she pulls away eagerly then a few seconds later the lack of power returns. This pattern has been consistent ever since. Ten to twenty mins of good running then no power. I have noticed that if I pull the choke out, the car runs much better....I thought this meant I had things too lean, so I richen the mixture and still the problem remains. I've checked and reset the float heights to no avail and now don't know what else to try. I can only describe it as feeling like fuel starvation.....but I'm guessing. Any ideas of what to try next would be greatly appreciated....
Thx, Mark
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Post by guidedog on Jun 24, 2015 21:24:53 GMT
Have you checked the fuel filter. It sounds like your carbs are filling you on choke can then run on them for a while. Then starvation. Have you got an electric pump ? which also can create the problem Another thing is a fuel leak between the tank and pump the pump can then suck air.
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Post by Phil Nottingham on Jun 24, 2015 21:42:56 GMT
Sticking needle valve if it has a Viaton tip as these swell & dissolve in modern E5 petrol
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Post by Roverboy on Jun 24, 2015 21:53:47 GMT
I had this problem wasnt till I took off the su found one of the springs had come off leaving one side on full choke
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Post by p5bdownunder on Jun 25, 2015 3:33:01 GMT
I've just resolved this exact problem with my car and it was a fuel starvation issue. The fuel filter on the engine was clean and yet it kept dying in the same way you have described. As it turned out, a previous owner had fitted two extra fuel filters just after the pick-up point from the tank, which were hidden in the boot behind the vanity panel. These were very dirty so were replaced. I also removed and cleaned the tank, although it was in good shape and actually didn't really need a clean. I replaced the electric fuel pump with a new 4-6psi pump, although it is quite noisy now. I will replace that again soon as it can be heard on tick-over when sitting at the lights, etc. and is annoying me now...! The carbs were stripped and one of the chambers had an excessive amount of fuel in it due to the float being set too high. This was adjusted back to the recommended level and now the engine starts better, runs beautifully and doesn't smell rich. So Happy Days...! But it does have an annoyingly loud fuel pump....! Stu Incidentally, I also discovered that my carbs are actually from a later P6B....
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Post by markymark on Jun 25, 2015 10:15:44 GMT
Hi Guys, Thanks for the thoughts. Fuel filter is maybe a year old, but will change and check all unions back to tank for leaks. I think the needle valves are ok but will take a look. Last resort is a new pump!
Will let you know how I get on. Cheers, Mark
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Post by guidedog on Jun 25, 2015 11:20:14 GMT
Hi Mark, I had a similar thing with a pump. Going fine then came to a hill crept up at 5mph on the straight ok. Pump was running but not fast enough. It was a new one. Beware some pumps are bl--dy noisy. There is a small facet pump that John W has which should do trick. I have got to change again, 3rd time.
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Post by enigmas on Jun 25, 2015 12:22:45 GMT
Hey Stu, I thought that lovely pristine car of yours didn't have any issues! As to fuel pumps, I like the simple Facet pump. It's solid state has no dramas and about the size of 2 match boxes. Bolt it on small rubber mounts below the fuel tank (its not a pull type pump, although it will do it) and forget about it for a decade or so. (I've got one fitted to my Magnette)
Mark it does seem from the description in your posts that both float levels may be too low, as your car recovers after a short period idling. It uses less fuel at idle so both fuel bowls fill once again and then deplete when you work the engine harder. Also check the flow capacity of the pump by dumping the fuel feed into a jar and noting how much fuel is pumped within 30 secs or so. You can then eliminate the pump if the volume is ok.
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Post by p5bdownunder on Jun 26, 2015 0:56:31 GMT
Hey Stu, I thought that lovely pristine car of yours didn't have any issues! ...it doesn't now, Vince...!
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Post by markymark on Jun 26, 2015 10:10:20 GMT
Hi Guys, Fuel filter removed and I can blow through it easily (yuck!) so don't think that's the issue. Plenty of fuel from tank to pump - confirmed by removing pipe and ending up with puddle on floor! No sign of any fuel leaks. If I run the engine with the pump output into a jar, how much should I see? Is there an amount per minute at certain engine speed etc?
Thx, Mark
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Post by enigmas on Jun 26, 2015 11:33:29 GMT
Mark there is a figure to indicate volume over a given time but if you observe what is pumped into say a litre container over a period of 1 minute, you'll probably find that the volume is greater than the engine can consume over this time. I'd be more concerned that the float levels maybe too low. You can also fabricate a simple gravity feed system with a given volume and see what transpires. (Obviously take care when doing this)
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Post by markymark on Jun 26, 2015 12:18:38 GMT
Hi Enigmas, Ive ordered a rebuild kit for the pump from JRW. Better to be safe than sorry. I have also reset the float heights, but that didn't make any difference. Thanks, Mark
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Post by lagain on Jun 28, 2015 20:52:51 GMT
If you remove the dampers from the carbs then lift the pistons with the little brass post at the bottom of each carb they should fall back easily. Until I had mine rebuilt I used to have to be very careful how I refitted the cover as the piston would stick. If you listen carefully with your head in the boot you may be able to hear the fuel splashing back into the tank !
Have you touched the fuel reserve handle ? A local member had fuel starvation problems for years and it turned out to be rubber in that tap disintigrating and restricting the flow of fuel
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Post by markymark on Jul 6, 2015 21:23:24 GMT
Well guys, I think I finally fixed it!
I took lagains advice and checked the movement of the Pistons in the carbs. All seemed well but I noticed that on one of them the top was fractionally misaligned? There are three screws and there's clearly a wide tolerance. I lined it up by eye and nipped up the screws. Now after a test drive all seems good. Fingers crossed.....
Thanks for your help....
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Post by johnwp5bcoupe on Jul 7, 2015 6:39:58 GMT
Well guys, I think I finally fixed it! I took lagains advice and checked the movement of the Pistons in the carbs. All seemed well but I noticed that on one of them the top was fractionally misaligned? There are three screws and there's clearly a wide tolerance. I lined it up by eye and nipped up the screws. Now after a test drive all seems good. Fingers crossed..... Thanks for your help.... The Chambers should be a snug fit on the body Mark the screws are only there to hold the Chambers down not to align The Pistons "should" be matched to the Chambers if not they will possibly stick? have a view of these roverp5.proboards.com/thread/6544/john-twist-su-carb-set
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