Fast idle

[427TJ]

Last summer I began burning a 50/50 mix of 100 octane low-lead aviation gasoline and 92 octane pump supreme in my stock, unrestored, 105,000-mile '67 Camaro 396/325. The car runs great on this brew, however, it began idling fast after about two or three tanks over a two-month period of pleasure driving. I back the idle adjustment (Q-jet) all the way off and the idle remains at 1300 or so. The car has the stock Th-400 trans and stock Chilton's manual-specs tune up. My four year-old son thinks it's neat when I put it in reverse to back out of the garage and the tires chirp but I'd like to get it back down to 700-800 rpm.

How come it's idling fast?

Thanks in advance.

Bill

[John]

....you may want check to see if there is a vacuum leak....that will cause a fast idle http://www.yenko.net/ubbthreads/images/graemlins/scholar.gif

[VintageMusclecar]

Bill;

Several things come to mind.

First, check for any obvious vacuum leaks. If none are found, make sure the choke mechanism is operating properly and it's coming off the fast idle cam completely once the engine is warmed up. Also check the primary throttle shaft for excessive slop, as this is a common problem on QJets.

See what you come up with and we can go from there.

Eric

[DaJudge]

It sounds like you may need a carb rebuild. The wells in the primaries are most likely leaking down and dumping fuel. This will cause a rich condition that will make adjustments impossible. When you get your Q-Jet rebuilt have the rebuilder redo and epoxy the primaty wells so they dont leak again. This is very common on q-jets and missed when inexperienced carb shops rebuild them.

[427TJ]

Well I couldn't find any obvious vacuum leaks--all the vacuum caps and hoses seem fine. The throttle shaft seems tight as well. The carb may very well need a total rebuild as it's been on there since 1967 and logged over 105,000 miles. I was just wondering--would the avgas have anything to do with it? It idled normally until my second or third tank with the 100LL mixed in, then this 1300 rpm thing started. Oh, and it's also slow to fire after shutting it off warm. During a hot re-start at a gas station, etc., it cranks for several seconds and then stutters to life and then runs fine--at 1300 rpm.

I know they're kinda' pricey but I was looking at the bolt-on Edelbrock Q-jet replacement carb as a possible fix rather than go through the potential agony of getting the Rochester unit rebuilt properly. Any advice on that?

Thanks again guys. http://www.yenko.net/ubbthreads/images/graemlins/biggthumpup.gif

Bill

[Seattle Sam]

Bill,

My guess is, the high level of detergents in the avgas removed all the varnish from inside your carb, and something inside has more clearance than it should. I would recommend you just buy the Quadrajet book and a rebuild kit at your local NAPA store, and rebuild it yourself. But with that high mileage, you might have issues you can't fix with a rebuild kit, such as worn throttle plate bushings.

Where are you in WA? There is a good shop in Kirkland (Totem Lake) that can rebuild your original, no agony involved. They have worked on Denis' Z/28 carbs, Alex really knows what he's doing..
Carburetor and Fuel Injection Connection, http://www.carbconn.com/

Good Luck!
-Sam

[427TJ]

Thanks for the info Sam---I was wondering if the avgas had "cleaned out" the crud in my carb. I'll look into the local Q-jet guy you recommended since I'm not confident I could get the thing back together if I did it myself! Actually, I probably could but I'd rather have a competent person do it. BTW, I'm down in Federal Way.