twin 40 Dcoe carbs running lean at power
Discussion
Hi dont suppose anyone has any advice do they? I have a pair of twin 40 DCOE's on my 1700 x flow engined westfield. On the rolling road a few weeks ago i was told it was running out of fuel at 5000rpm and that it was prob the fuel pump that wasnt man enough for the job. I've swapped the pump and its giving juts over 3.5 psi at the carbs and flows 23 gal per hour but is still having the same prob and seems to be runing out of fuel when your in 4th gear. It'll rev quite happily to 7000rpm in all the other gears but if you put it in top and hold it out down a straight it'll get to 5000rpm cough splutter like its out of fuel, if you lift and give it a few seconds it's fine again and you can hold it constantly at just undr 5000 without any probs.
could it be a blocked internal passage in the carb?
could it be a blocked internal passage in the carb?
I would have though a fuel pressure gauge to confirm that you are still getting fuel delivered when you are having the problem would be a good idea, they are not expensive and can save a load of time in diagnosing problems, if you want any suggestions on appropriate gauges or easy installation then let me know
Do you have a fuel pressure regulator? I have a filter king on mine. If you undo the top two nuts and give the stud inside a twist you can up the fuel pressure to the carb.
Beware if you have too much fuel pressure it can overpower the valve in the carb and push the floats down. Thats pretty obvious as if you turn the ignition on and let the pump fill the bowls they will overfill and fuel will dribble out the trumpets.
There is always the guideline about however many psi but I set my fuel pressure by getting the max pressure before fuel started to leak then back a 1/2 turn to be sure. That way it may not be in guidelines but it certainly is as high as the carb can take so should never suffer starvation when the bowl is being emtied at a rapid rate.
Beware if you have too much fuel pressure it can overpower the valve in the carb and push the floats down. Thats pretty obvious as if you turn the ignition on and let the pump fill the bowls they will overfill and fuel will dribble out the trumpets.
There is always the guideline about however many psi but I set my fuel pressure by getting the max pressure before fuel started to leak then back a 1/2 turn to be sure. That way it may not be in guidelines but it certainly is as high as the carb can take so should never suffer starvation when the bowl is being emtied at a rapid rate.
Have you checked the float level, has the problem just started? If the float level and fuel delivery is OK a then maybe the carbs need cleaning out or you may have an ignition problem unless it was checked with a CO meter on the rolling road.
If everything is OK so far then try changing the air corrector jets in the top of the emulsion tubes first as these affect top end power although I would think they would cause only minor mis firing.
What car, engine, jets, emulsion tubes and air correctors are you using and how long has it been happening?
If everything is OK so far then try changing the air corrector jets in the top of the emulsion tubes first as these affect top end power although I would think they would cause only minor mis firing.
What car, engine, jets, emulsion tubes and air correctors are you using and how long has it been happening?
twistedsanity said:
if it will rev happily to 7k in every other gear i dont think the fuelling is your problem, the fuel supply system has no idea of what gear the car is in so why should it behave differently in top gear only?, how is the fuel tank mounted? maybe a pickup problem in the tank?
Yes it does,engine load changes from gear to gear,wind drag etc etc
check the little fuel strainers near the fuel inlet Banjo unions too.Edited by That Daddy on Friday 25th July 16:22
twistedsanity said:
if it will rev happily to 7k in every other gear i dont think the fuelling is your problem, the fuel supply system has no idea of what gear the car is in so why should it behave differently in top gear only?,
Because the engine is under a higher sustained load in top.I found with twin 40 DCNFs I had a similar problem on the Quantum, turned out to be a failing fuel pump too
Dont know what fuel pump you're running, sounds like a Facet, not sure which one. Is it a red top? Thats probably what you're going to need from the sounds of it, and a regulator with a guage if not already. The red tops have larger unions for uprated fuel pipes, you can get adapters for the regulator if needed
Dont know what fuel pump you're running, sounds like a Facet, not sure which one. Is it a red top? Thats probably what you're going to need from the sounds of it, and a regulator with a guage if not already. The red tops have larger unions for uprated fuel pipes, you can get adapters for the regulator if needed
i'm running a facet pump one of thos solid sate type competition type pump supposed to 5 to 7 psi. i removed the fuel regualtor whe o nthe rolling road t orey and get the fuel flow up. made no difference. we did play around with flaot heights and we beleive these are set OK now. I think i solved the prob now, well sort of. I drilled out the inner bore of the fuel poipe tee piece that runs bvetween the two carbs as the main feed was about 1.5 mm smaller diam than the other two. I also carb cleanered the jets and orifices oout in the carbs. Took it out ona run on saturday and now the splutterign has moved further up the rev range to 6K which for the moment ithink i can live with. thanks for the advice guys
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