hesitation,bogging during acceleration
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hesitation,bogging during acceleration
i have a 77 f350 with a 5.4 330HD Fe engine.It was missing all the time and i found i had a bad exhaust valve and guide at #7 cylinder.Took off the heads and had a vavle job done.The carb was leaking fuel all over so i decided to put on a rebuilt.It used to accelerate pretty good before but now with the new carb it coughs , puckes and stumbles untill the rpm's climb then it runs good.It has a very good idle.I tried adjusting the holley 2 barrel carb but i can turn the screws all the way in with no response,so i am not sure how to tune it.
I set the timing at 550 rpm,to 10 degrees BTDC.(not sure if this is 100% correct because i could not locate the specs,there was no sticker on the truck anywhere)i checked and the advance works fine and cant find any vacuum leaks to speak of.All the plugs and wires are new.
I have been fiddling with this problem for weeks now and i am not sure what else to do or check.
I set the timing at 550 rpm,to 10 degrees BTDC.(not sure if this is 100% correct because i could not locate the specs,there was no sticker on the truck anywhere)i checked and the advance works fine and cant find any vacuum leaks to speak of.All the plugs and wires are new.
I have been fiddling with this problem for weeks now and i am not sure what else to do or check.
Tuned
Joined: Feb 2003
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From: Cincinnati, Ohio
Is the new carb an exact replacement? If you can turn the idle adjustment screws in all the way and no change in the idle then you are probably leaking air under the carb probably at the intake. Do you have a vacuum gauge, what is it reading at idle? Just a comment, but if you have a leak at the intake that can over time cause a burned exhaust valve.
John
John
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is was not an exact replacement,just a basic rebuilt holley 2 barrel,the screws will turn all the way in with no affect on the idle.I was very careful installing the heads and intake,i will locate a vacuum guage,how much should i have at idle?
want to make it right and dont want to damage any of the new valves.
are there any areas that are prone to vacuum leaks?
want to make it right and dont want to damage any of the new valves.
are there any areas that are prone to vacuum leaks?
Tuned
Joined: Feb 2003
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From: Cincinnati, Ohio
You should have at least 18 - 20 inches at idle in neutral. Where the intake meets the heads, base of the carburetor. Also, check all vacuum lines because if they leak it effectively is the same as leaking at the carburetor or intake. Air being sucked in under the carb is not part of the carb metering system so it will tend to lean out the fuel mixture.
John
John
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From: Louisville,Ky.
Some Holley's have a reverse idle circuit that turning in the mixture screws will not lean out the mixture. Try backing the screws out and see what happens. It may just need bigger jets in it.
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it did affect the idle when i turned the screws out pretty far,but i wasn't sure if they would have a stop or just fall out.
I just screwed them out untill the idle was pretty good,but had the really bad hesitation problem at lower rpm's,seeming to smooth out at high rpm's.
i dont know if it is a vacuum leak or this "rebuilt" carb might be a lemon.
I just screwed them out untill the idle was pretty good,but had the really bad hesitation problem at lower rpm's,seeming to smooth out at high rpm's.
i dont know if it is a vacuum leak or this "rebuilt" carb might be a lemon.
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Tuned
Joined: Feb 2003
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From: Cincinnati, Ohio
I would definitely get vacuum readings so that you can eliminate that as a possibility for your problems. You can use propane to find a vacuum leak if you like. I have used propane, sprayed WD-40, etc., to try and locate a vacuum leak.
John
John
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I put a vacuum guage on it today and it reads a rock steady 16 inches at idle,when you step on the gas it goes to 24 and upon quick release of the pedal it goes down to 5 then climbs right back up to 16 as the engine returns to idle and stays there solid.
so,i dont think i have a vacuum leak,maybe this carb is a piece of junk.
so,i dont think i have a vacuum leak,maybe this carb is a piece of junk.