nhlgopens

Car runs great - small issue is when sitting at dead stop, idle is around 800rpm. After sitting for about 10 to 15 seconds, it runs up to about 1500rpm and sits there. Doesn't like to come back down unless I put friction on the clutch to drop the rpm's. Any idea's? The engine completed total rebuild - so did the qjet.


[Modified by nhlgopens, 5:54 AM 7/2/2004]

Jvette73

Worn or broken dist advance springs or perhaps ones that are too weak. It could be advancing the timing at idle making the rpm go up. Do you have the dist vacuum hooked to ported or manifold?


[Modified by Jvette73, 6:08 AM 7/2/2004]

nhlgopens

The vacuum advance line is hooked to the vacuum relay <I think that's what it is> on the manifold to which has two lines from the carb. Should I remove and go directly to carb?

Boofers

That your mech advance may not be springing back but it could also be a dirty main shaft in your distributor. Take the cap off your distrib and make sure that when you twist the rotor by hand it easily springs back to place by itself. If not you could spray some WD40 under the pickup to free up the shaft or even better take the distrib right out and apart & clean the gunk off the shaft so it spins nice and smooth.

Could also be that your Q0Jet throttle plates need to be bushed - is there any side to side play in your primary throttle plates?

Good Luck


[Modified by Boofers, 7:43 AM 7/2/2004]

sjr1971

Mine goes directly from the pass side port on the Q-Jet to the vacuum adv.

nhlgopens

I checked the distributor's mechanical advance and everything was nice and smooth. The throttle plates don't have any side to side play. Is it possible that the vacuum advance isn't working correctly? I'm going to try the vacuum line directly from carb to see if that helps.

Boofers

On top of your idle problem if you are having hesitations, bogging, stumbling or flooding that would point you towards the carb for sure (leaky needle & seat, sticking power piston, incorrectly set float).

Another possibility is a vacuum leak. You mention your Q-Jet was recently rebuilt - if you don't find the answer here is something you could check. I am quoting Lars here by the way...

Wrong throttle plate gasket results in: Poor idle, erratic idle, ineffective idle mixture screws, symptoms of a vacuum leak.
Comments: There are several different designs for the throttle plate gasket, and they do not interchange. Two common problems occur: The first problem was addressed in a GM Service Bulletin around 1971. There is a difference in the open area in the gaskets just forward of the centerline of the primary throttle holes. Some later carbs use a gasket with a larger open hole in this area. If this gasket is used on an earlier carb, you will end up with a massive, undetectable vacuum leak. The other problems with these gaskets occur due to the idle fuel and vacuum bleed holes not lining up from one design to the next. Use of the incorrect gasket can result in blocked idle fuel and blocked vacuum signals. Always lay the gasket onto the float bowl and onto the throttle plate to check the hole alignments."

nhlgopens

I think I got it fingered out... did some further reading and decided to try multiple things. First... re-adjusted air mixture screws - 1 1/2 turns out... reset idle... did away with the vacuum relay and plugged advance line directly into the pass. side of carb. Drove to work this morning through town and so far it's running great. No high idling at stops. Although typical cold natured beast took a few minutes to reach optimum running....

Jvette73

Maybe you just need a stronger return spring. The one you have might be worn and week. Next time it happens, open the hood and pull the throttle linkage back towards the closed position. If it slows the idle I bet a stronger spring would help. Also make sure the choke flap is not fully open and the fast idle cam is not on a higher step.