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it stalls . . .
I have been unsuccessful in getting answers or ideas on what is causing the stalling issue I found with my car.
Although it runs quite well and has no hesitation, I noticed on a quick stop or turn to either direction or long turn taken quickly, like an off ramp, the RPM's drop to the point of stalling, if I put it to neutral or clutch it and don't touch the gas. I noticed that the fuel in the fuel bowl sight glass was halfway up, which is where Quick Fuel says it needs to be. But Keith Craft Racing told me to lower it to the bottom of the sight glass, which I did, but it made no difference. Any ideas where to go to next? Other data: Shelby FE 527 built by Keith Craft Quick Fuel Q850 carburetor Idle was 1200, I just lowered it to 750-800 Fuel pump: Holley HP125 @ 7PSI (gauge shows 5.5-6.0 PSI) 850 CFM May be a little rich, but seems to run great |
Why did you lower the idle? What's your cam specs?
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Could be fuel slosh or starvation. With the idle that low you probably have the butterfly's almost completely closed. It won't take much excess fuel or lack of to cause a problem.
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That's kinda what I was eluding to...if the thing has a decent size cam in it and he tried to idle it down to 700-800 revs, then it may not want to run at that speed...
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It acted the same way at the 1200 RPM idle. . . ., only it had more RPMs to drop before stall. . .
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Ok, did you try raising the float levels?
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Not since they were at halfway up the sight glass. I guess that's logical, I'll give it a shot. . .
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Is this a new motor? Mine started stalling on me soon after I got it and discoverd the jets were two sizes to big. After dropping the jets down, all was fine.
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That being said, how do I know what the correct jets and fuel mixure should be? |
I wish I could tell you. Get the name and number of your carb and call the manufacture and order two sizes of jets. One stock size and one small size. I would guess that your presently running a larger than stock jet. Good luck
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Find a place where you can do a hard corner and get it to die. Shut the motor off right away and check the fuel bowls to see if they are empty or over filled. I had a problem at hard accelaration the car would die since the fuel pump would suck air.
Scott |
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I think XLRO8R is correct- you may need some jet extensions. http://store.summitracing.com/egnsea...=KeywordSearch |
What do the jet extensions do?
Keith Craft dynoed my enigne and I assume it's the carb that was used, although it did not smell like fuel. However, they told me it would not due to the race gas they use. But I also heard that they tend to leave it running a little rich to be safe. I do have the dyno sheet, but how do I measure the A/F ratio at home? I think we are talking about two issues. I think the stalling is unrelated to the misxure, since it does run well. I think the stalling, since it is only under g's (not that much mind you) is related to too much fuel in the bowl or two little fuel in the bowl. I never do see black smoke, as I would think I would see if fuel was being dumped in. Do Holley's have this problem? |
Yes, we are talking about 2 different things.
Jet extensions- From the sumimt catalog- (I bolded the relevant language) "These Holley main jet extensions feature a new design that actually screws into the metering block. The main metering jet threads into the end of the extension, moving the fuel entry point for the main jet out into the the fuel bowl. When it's in this location, it cannot be uncovered preventing a lean condition during periods of extreme acceleration or braking." And yes, Holleys have the same problem. As for the a/f ratio, your dyno sheet should have a line with the a/f mixture right on it. To measure it at home, you need to get an exhaust gas analyzer and stick it in the tail pipe or install an O2 sensor in the pipes and take a reading with that. |
Rob ~ did you call Keith??
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I had the same problem with my Holley HP 1000CFM with road race floats and jet extensions. I ended up buying a BG 850 and still had the stumbling problem in hard corners. I hooked up my A/F meter to see if was leaning out or running rich in corners. It was flooding in corners. So I keep lowering the floats till it stopped, but that ended up being a way to low. I set them at the lowest point in the sight glass. It isn't perfect but it is close. Keep in mind when you raise or lower the floats, it will change you A/F at idle. The best place to test it ended up being a parking lot at a business park on the weekend.
Scott |
When in nuetral and on the brakes hard will it keep running if you hit the gas pedal? If not it may be an electrical short from a loose or hanging wire.
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You have a dynamic problem-Keith would not have seen that on the static dyno.
Scooter has it exactly right: "It was flooding in corners. So I keep lowering the floats till it stopped, but that ended up being a way to low.' Don't touch the floats other than the way Keith had them. The cure is not jet extensions but rather vent whistles. They prevent fuel from sloshing into the vent passages in the main body and drowning the the carb(s). They're cheap and easy to install once the bowls are off. Having an effective cold air system sealed to the hood will cure the problem totally. If you do nothing just be ready to clutch in and blip throttle while stopping/turning. |
I had my carb looked at by a good carb tuner and we found the inside to be set up with vent whistles and everything to be set up right, just that it was jeted for the dyno and not the street.
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