small block chevy running rich....cam timing?

jeepn-jason

jeepn-jason

Well-Known Member
Joined
Mar 20, 2005
Location
Greensboro
Alright gonna be a long post here, i have started restoring a 64 impala my dad has had for about 30 years. He built a 350 for it about 15 years ago. It came out of a 70 chevelle, was origanally a 300 horse motor. It was bored 40 over with the heads redone, a performer rpm intake, hei dist, headers, and now a holley 600. Ever since the engine was built it has always run very rich. It will burn your eyes after it has ran in the garage for a few minutes. Plugs are wet and black. He has tried different carbs throughout the years and they all run the same. I have tuned the carb thats on it now with a vaccum gauge and its no better. Would the cam being advanced too much be causing these problems? I noticed the exhaust is getting hot too. :beer:
 
1.Hot exhaust is caused by a lean condition
2.What heat range spark plugs are you running ?
3.What is the vaccume reading at the intake ?
4.What is your timing set at ?
5.What type of fuel pump mechanical or electrical?

A rich or lean condition could be caused by sevral things
exhauts that burns your eyes is lean
 
Its def running rich. The plugs are wet with gas. Mechanical fuel pump. Vaccum is good, i cant remember what it was but its good. Plugs are ngk for a 70 chevelle 350. Ive never heard of lean conditions that burns your eyes....it reeks of fuel.
 
Im thinking that the cam is advanced too much causing the combustion to take place in exhaust. The intake valves are staying open past the combustion? Idk just my theory, hoping someone else has had this problem, and similar results....
 
Try a new or smaller power valve. If the engine "coughed" during the new start up it prob blew the power valve. Its easy to change, just take off the front fuel bowl then the metering block. Use a 1" wrench to take it off. Make sure the gasket is round outer and a triangle inner hole. I've seen some make a mistake of running the round inner and it would run rich.
 
What Holley are you running? You need to be sure it has a Holley power valve, probably need a 65 or 6.5. Have you tried dropping your main jets? Also need to make sure that the idle is not too high. If so, it will pull fuel from other circuits rather than the idles circuit. But most likely you will need to bush the IFR in the metering block.
 
It IS a rich condition that burns the eyes. It's the holley that is running rich. Not dogging Holleys, I love them. Just needs to be jetted down. They are jetted rich from the factory. However, I would also try running in the idle mixture screws. My guess is they are too far out. Try them 2 1/4- 2 1/2 turns out from fully seated and go from there. I really doubt it's the cam timing. Was the cam not installed straight up? You might also try a tad more ignition timing..be careful of too much, though.

If the plugs have been fouled, change them. They definitely won't get any better, even with cleaning.
 
BigTex383 said:
It IS a rich condition that burns the eyes. It's the holley that is running rich. Not dogging Holleys, I love them. Just needs to be jetted down. They are jetted rich from the factory. However, I would also try running in the idle mixture screws. My guess is they are too far out. Try them 2 1/4- 2 1/2 turns out from fully seated and go from there. I really doubt it's the cam timing. Was the cam not installed straight up? You might also try a tad more ignition timing..be careful of too much, though.
If the plugs have been fouled, change them. They definitely won't get any better, even with cleaning.
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Like i said, this has been a problem for a while now. It has had qjets,a carter, an edelbrock and 3 holleys on it. All of these carbs were off of know running vehicles that ran great. The last set of plugs were in it for 5 minutes. The idle mixture screws are 1 and half turns out to start with, and with the vaccum gauge connected i backed out each about a 1/4 turn more to acheive more vaccum at idle. I am stuck on it not being the carb. I have a truck avenger that came off of my buddies stock 401 amc that im gonna try this weekend.
 
jeepn-jason said:
Like i said, this has been a problem for a while now. It has had qjets,a carter, an edelbrock and 3 holleys on it. All of these carbs were off of know running vehicles that ran great. The last set of plugs were in it for 5 minutes. The idle mixture screws are 1 and half turns out to start with, and with the vaccum gauge connected i backed out each about a 1/4 turn more to acheive more vaccum at idle. I am stuck on it not being the carb. I have a truck avenger that came off of my buddies stock 401 amc that im gonna try this weekend.
Click to expand...
I also have a Chevy 350 my son changed the cam and since then it has been doing the same thing, after a couple of minutes it fouls plugs. Definatly cam related I am a professional mech and had this vehicle running great before he did the cam swap and I know all systems inside and out, find out what cam is in it and it's probably wrong for the set up
 
Fast forward 6 years, I've got it running great now. I don't really know what has fixed it but the engine is unchanged internally. I have swapped the carb, ignition, fuel lines, tank, pump ect.
 
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