Setting Idle

[BrianB]

Apparently the guy who did the "emissions test" messed with my carb settings. It idled great before, but now when in gear it drifts down from 1000 rpm to 800, to 700 and on down until it eventually dies. When in neutral it's ok and stays around 1000. L82, Qjet with 10:1 pistons and a cam that I don't know a lot about. It's a racing cam. Not sure if it matters, but I'm at ~5,000 feet elevation. If there's a Qjet book for dummies, I'd like to get one. Or a real manual. Any help would be great!

 

[drags1998]

Before you dive into the carb. Take a VERY close look at all of the vacume lines, It sounds like someone left a line off somewhere!!!!!

 

[76L82]

Brian - I have the same car that you do but you have more compression from you engine than I do. Actually, I run into the same problem pretty frequently. I am sure you know this but simply adjust the idle screw until you get it where you need it. Strangely enough, I usually fight just the opposite problem in mine...it tends to creep up in RPM's until it is around 1500 RPM in nuetral and continues to diesel when turned off.

 

[BrianB]

It's been tough to start also. Lots of smoke and not firing right until it warms up some. I haven't checked timing, I'm thinking that's next.

 

[76L82]

Brian - I am sure you have done this but it truly is worth getting as best a "baseline" for your Vette as possible. As a starter, when I first got my Vette and she was doing what you described I bit the bullet and bought all new plugs, wires, hoses, filters, emsissions stuff (egr, pcv, etc.). Not cheap but it is worth it in the end.

Before setting the timing, I fired her up and let it run for a few minutes then put my timing gun on it. Recorded where it was, and started to set more advance...for whatever reason, my car tends to do better with more advance. Anyways, this seems to have been a pretty effective remedy as it doesn't have the same problems that it used to have.

If you don't do this, what you get is every time you run it, you're trying to compensate for bad timing and the need for a tune-up by fooling around with the idle setting....trust me, I have tried doing this many times and it just doesn't work.

 

[curtis]

Definately sounds like tune up needed. With big cam and high compression you will most likely need at least 10 degrees static advance. Your cam will be pulling very low vacuum at idle and hence idle mixtures are screwed up from low air flow thru carb. If you take carb off for some reason, look and see the slots in barrels are uncovered too much. this is from idle screw turned up to compensate for low vacuum draw on idle circuitwhich richens idle mixture. may need to drill hole in throttle valves to enable enough air to come in at idle so you can set your mixture screws correctly. Are you sure your cataclysmic coverter isn't plugged? I saw other threads in this forum about carburetors.

 

[BrianB]

It's not the converter, there isn't one. Straight pipes through mufflers out the back. I'll do a tune up soon and see where that gets me. I have the screw set pretty close to where it was. It still idles a little high, but it's close to where it was when I got it. It's just pretty finicky.