Help! Car won't Idle

[racingundertaker]

I have been driving my 73' Vette for a couple of weeks now after taking it out of storage. It ran fine for a few weeks, and then seemed to idle very rough when I had it in gear. I have a 350/auto w/Lunati .477 lift cam. The car does have a "lopey" idle, but it got progessively worse at times but then would smooth out again. The Q-Jet was rebuilt last summer; spark plugs look great. New wires, cap, etc. The car pulls and runs fine under a load. Now this evening I went to take it for a ride, and it wouldn't even idle out of the garage. It started hard; seemed like it flooded; once I held it to the floor, the engine cleared out in a big blue/black puff of smoke. It would idle for a few secs and then just sputter out. The exhaust after it does this smells like a car after it "diesels" when shut off. Does anyone have any ideas what this might be? Is it carb related? Coil related? Timing related? Any help or ideas that anyone can give me would be greatly appreciated! Thanks for all your help!

 

[ICP777]

How many tanks of gas have you ran thru her since you pulled her out of storage? I would change the fuel filter first.

MATT

 

[Jimmy Vette]

Idle

I have an 80 coupe & the same sort of thing happened last year when I took it out of storage. Idle was rough & black smoke. I changed the fuel filter & it was not much better. Then a friend told me that it could be a sticking valve. I put valve cleaner in the gas (Lucas brand as I recall) & also put an engine valve cleaner into the crank case. Drove it for around 50 miles & things smoothed out fine. I had no problems this spring. This may not be your answer, however it was a very cheap fix that worked for me. Lucky I guess.

 

[RodsnRides]

I suggest you first turn in your idle scres and count the number of turns to stop (~3). Then back out both screws, and GENTLY force compressed air into your idle passages to blow them clean. Inspect the screws (not bent/broken) and put them back in and adjust to normal turns out.

Then start it up, hook up a vacuum gauge and idjust your idle then. Also check to see if your distributor vacuum diaphragm is working, and if it should have vacuum at idle. It's possible the diaphragm is out, so you not only have a vacuum leak, but you are also not getting that timing increase at idle.

It's also possible you may have a bad float in the carb. Good luck!

Rick

 

[anips]

I suggest you first turn in your idle scres and count the number of turns to stop (~3). Then back out both screws, and GENTLY force compressed air into your idle passages to blow them clean. Inspect the screws (not bent/broken) and put them back in and adjust to normal turns out.

Then start it up, hook up a vacuum gauge and idjust your idle then. Also check to see if your distributor vacuum diaphragm is working, and if it should have vacuum at idle. It's possible the diaphragm is out, so you not only have a vacuum leak, but you are also not getting that timing increase at idle.

It's also possible you may have a bad float in the carb. Good luck!

Rick

The ported outlet on a Q-jet is dsigned not to allow vac. until the throttle is opened, it draws from a opening above the throttle blades, to check the vac adv. dashpot use a mighty vac or blow into the hose, if you can blow through its bad, Q-Jets used two types of floats, a solid plastic or hollow metal one, over time the plastic one swells up and hangs up in the float bowl, this is brought on over time by being wet then drying out, if its the plastic float replace with a metal one.

 

[GerryLP]

I have been driving my 73' Vette for a couple of weeks now after taking it out of storage. It ran fine for a few weeks, and then seemed to idle very rough when I had it in gear. I have a 350/auto w/Lunati .477 lift cam. The car does have a "lopey" idle, but it got progessively worse at times but then would smooth out again. The Q-Jet was rebuilt last summer; spark plugs look great. New wires, cap, etc. The car pulls and runs fine under a load. Now this evening I went to take it for a ride, and it wouldn't even idle out of the garage. It started hard; seemed like it flooded; once I held it to the floor, the engine cleared out in a big blue/black puff of smoke. It would idle for a few secs and then just sputter out. The exhaust after it does this smells like a car after it "diesels" when shut off. Does anyone have any ideas what this might be? Is it carb related? Coil related? Timing related? Any help or ideas that anyone can give me would be greatly appreciated! Thanks for all your help!

When I had the Q-Jet running with the computer, the choke would get stuck sometimes after start-up in the mornings. I used the same procedure as you did to clear it out if it happened to me while out driving. So, check the choke. Also if the car was stored a long period of time, resto-fuel fuel or something like that will help restore the fuel if you had alot of it in the tank for such a long period of storage.

GerryLP:cool

 

[racingundertaker]

Well, the problem with my "hotrod" was finally diagnosed. After going through all the obvious things to look at (i.e. timing, plugs, etc.) a more detailed examination revealed a major choke adjustment needed. Once that was done, the car had now developed a dead cylinder and much concern on my part. Upon pulling the left side valve cover, it was discovered the valve spring on the #1 exhaust valve was cracked/broken . The good news is that nothing was damaged internally; a new valve spring is on the way; and hopefully I will have my "hotrod" back on the road this afternoon. I had the same problem last year at almost the same time with the #4 cylinder intake spring. I can't figure out why this happened again, probably just coincidence? It is a hydraulic set up and I do turn the engine over from time to time during storage. Oh well.......hopefully it will hold together for the rest of the summer, and then I will have an even better excuse to remove this powerplant this fall and convert it into a 383 stroker. Thanks for all the suggestions and help! This forum is great!

 

[fine69]

Well, the problem with my "hotrod" was finally diagnosed. ...a more detailed examination revealed a major choke adjustment needed. Once that was done, the car had now developed a dead cylinder and much concern on my part. Upon pulling the left side valve cover, it was discovered the valve spring on the #1 exhaust valve was cracked/broken . The good news is that nothing was damaged internally; a new valve spring is on the way; and hopefully I will have my "hotrod" back on the road this afternoon. I had the same problem last year at almost the same time with the #4 cylinder intake spring. I can't figure out why this happened again, probably just coincidence? It is a hydraulic set up and I do turn the engine over from time to time during storage. Oh well.......

Hi. I just had this happen to with a brand new aluminum head. I contacted Edelbrock and Summit. Hopefully one of them will send me a replacement spring and pushrod.

Did you ever find out why you experienced the broken valve springs?