idling/timing problem
Thread Starter
Le Mans Master
Joined: Oct 2000
Posts: 6,209
Likes: 33
From: Texas-out west
idling/timing problem
small block that idles very rough, timing doesn't want to set right, vac reads very low-around 5-7 and car does has stock mild cam. when over 1000 rpm smooths out and drives good. plug wires ohm out good, plugs have good spark, fuel mixture looks good, plugs look right and are not fouled. could it be vac leak?? I can't find one anywhere and hear not hissing sounds. could I have a leak on intake?? I did change gasket but no sounds of a leak or rpm increase when I spray wd40 along the edge. thanks.
Race Director
Joined: Oct 2005
Posts: 12,468
Likes: 1,548
From: Camp Verde AZ
C1 of Year Finalist (performance mods) 2019
2017 C1 of Year Finalist
Is this somethign that suddenly happened, or has it been this way?
if suddenly happened, what do you do prior to it happening?
if gradual, or it always was this way, i supsect a high mileage engine with bad valves or misaligned cam.
Doug
if suddenly happened, what do you do prior to it happening?
if gradual, or it always was this way, i supsect a high mileage engine with bad valves or misaligned cam.
Doug
Melting Slicks
Joined: Oct 2004
Posts: 3,345
Likes: 87
From: Northern MN
St. Jude Donor '13-'14-'15-'16-'17
small block that idles very rough, timing doesn't want to set right, vac reads very low-around 5-7 and car does has stock mild cam. when over 1000 rpm smooths out and drives good. plug wires ohm out good, plugs have good spark, fuel mixture looks good, plugs look right and are not fouled. could it be vac leak?? I can't find one anywhere and hear not hissing sounds. could I have a leak on intake?? I did change gasket but no sounds of a leak or rpm increase when I spray wd40 along the edge. thanks.
What carb are you running? If it is a Holley you might want to check the float level on the rear. That was my problem. It wouldn't idle and I couldn't get the timing to set correctly. I found out that the fuel pump was fluctuating between 9 to 12 lbs of pressure. Holley calls for about 6 lbs. It would force fuel by the needle and seat on the rear and overfill the rear bowl. That allowed excess fuel into the carb and it wouldn't idle. The vacuum was down on my car to the same reading as yours. Carried only 5-7 Hg at idle. When I got the new fuel pump and installed it the float level corrected and the vacuum came up to 9 to 10Hg at idle. Just a thought of what else you might check.
Steve
Instructor
Joined: Nov 2007
Posts: 196
Likes: 0
From: Iowa
Holley?
Bad power valve?Holley only.
Carb base gasket leak?
Quadrajet may require metal gasket between carb and intake to keep exhaust passage from burning up the base gasket.
Brake power booster internal leak?Plug hose temporarily.
Manually close choke or put hand over carb while idling and see if it smooths out. That will indicate a lean idle, which is probably a vacuum leak, or a plugged idle circuit in carb. Take out mixture screws and spray a little carb cleaner then blow out with compressed air. Always turn screw in till it stops,first, counting the turns so you can set it back to the same place, even though it may not be correct.
Just a few starters.
Carb base gasket leak?
Quadrajet may require metal gasket between carb and intake to keep exhaust passage from burning up the base gasket.
Brake power booster internal leak?Plug hose temporarily.
Manually close choke or put hand over carb while idling and see if it smooths out. That will indicate a lean idle, which is probably a vacuum leak, or a plugged idle circuit in carb. Take out mixture screws and spray a little carb cleaner then blow out with compressed air. Always turn screw in till it stops,first, counting the turns so you can set it back to the same place, even though it may not be correct.
Just a few starters.
Pro
Joined: May 2004
Posts: 669
Likes: 0
From: CA
Loose timing chain? Or another possibility is that there may be damage to the cam and/or lifters. Modern motor oils have had all of the zinc removed in the last few years and the continued driving of your car without an additive will wipe out the cam in short order.
