M4ME carb stumbles sometimes dies when letting off throttle in gear - Hot Rod Forum : Hotrodders Bulletin Board
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Old 08-29-2007, 01:38 AM
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M4ME carb stumbles; sometimes dies; when letting off throttle in gear

hello

i just got done totally completey rebuilding the stock original LG4 305 engine in the 85 El Camino SS and it is .030 over and stock 4416 heads and so on

it runs strong and awesome and everything is fine
-even no check engine light or anything-
but for some reason (after i cleaned out and reassembled the E4ME carb) it would stumble and sometimes die when letting off the pedal to come to a stop-
it doesnt do it in park or neutral at all, it is perfectly fine at those times.

originally the carb was flowing over the top too much fuel,
in which is why i disassembled it,
to replace the float, needle, seat, and the airhorn gasket


and at first it wasnt doing this stumbling at all, it was absolutely perfect running

but after the engine got good and hot(almost 220 degrees at 97 degrees outside temp and brand new 3 core copper radiator) it started doing this stall/stumble

and now it does it when its not hot too


any ideas ?

theonly thing i can possibly think is that when i unscrewed the vertical "power valve" limiting shaft screw thing at the primary rods and float bowl filler block that i ddnt count exactly every thread i may be one thread off ? i counted 17 turns to remove it
so i put it back at 17

i took another E carb apart and it was only about 14 turns
it was two years different in model year age, identical carb


screwing it down into the carb too far would keep the primary rods from coming up high enough to be rich enough correct ?

it makes sense that this is a primary lean drop off problem of some sort.

but its odd to me that it only started doing this after it got very warmed up the first time, and ever since then.

this all happened today, since noon to now,


should i try unscrewing this primary rod limiting screw a couple of turns out ?



(front air dam spoiler removed for now)


i would need details on what to try, or what parts to check, as i am very used to the M series carbs
but not these E series,
the E series have so many more and different parts than the old M series, its pretty wild,.


thanks for anything i can try or check


also: why is there no carb section/board

i see quite alot of carb specific posts in the middle of everything


or is there a carb board i am not seeing?

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Last edited by fast68; 08-29-2007 at 02:28 AM.
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Old 08-29-2007, 02:47 AM
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A thought comes to mind, the fuel pumps on the common LG4 engines like the Elky, Camaro, monte`s, etc. were junk from the factory, they barely could keep up the fuel demands of a stock engine. If your still using the factory pump, or even a replacement stock pump then it`s likely the problem or is contributing to the problem. A carter replacement pump is recommended and usually cures any fuel problems. another thought is too low of float level, when you brake the fuel moves forward and if the level is too low from the fuel pump or float level it uncovers the idle circuits and the engine shuts down. Other than that the next thing that comes to mind is a vacuum leak. It doesn`t seem likely to me if it were to be one turn off that it would cause the issue. If in any doubt, back off it off half a turn, if the problem persists or gets worse, 1 turn the other direction, if it seems to get better another 1/4 at a time until it`s right. I found in the past since I didn`t have diagnostic tools to diagnose these carbs, I just used the trial and error method. Regardless, I would still change the fuel pump.
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Old 08-29-2007, 02:58 AM
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hmm i dunno


the fuel pump is brand new

it seems to pump TOO much fuel

you should have seen all the crazy tons of fuel spilling out over


and in VERY short order



it was bad

way too much

its definitely supplying more than enough pressure and volume, both



i really dont believe i have a fuel supply issue at all, i would dare to say thta i have the opposite problem, and too much fuel, but at least now we have a good working float, needle, and seat, unlike originally,


the stumble is on immediate deceleration, and not acceleration whatsoever

see what i mean


it runs so great now, all except this stupid stumble at deceleration now

when you are accelerating donw the road and then let off the gas pedal completely it will drop the rpm way down and almost kill the engine, but most of the time it barely recovers to idle again, all while in gear going down the streeet

doesn do it out of gear, any other time at all




thanks!

Last edited by fast68; 08-29-2007 at 03:09 AM.
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Old 08-29-2007, 03:36 AM
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If the needle and seat have trash in them and is stuck open it`ll overflow out of the top at idle almost regardless of how low the fuel pressure is. Is there any indication it`s flooding when you deaccelerate? One more question, is the carbon canister still in use? is the line that goes to the carbon canister connected, open or plugged off?
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Old 08-29-2007, 05:57 AM
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I tend to think that the fuel pressure is too high for the carb. I had the same problem with a Chrysler 318, the engine would idle fine for a few minutes then slow and stumble, and stop, because the fuel pressure from the replacement Electric pump was too high and overcame the carb shut-off needle valve flooding the engine. Reducing to 3/4 lbs pressure cured the problem.
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