after new carb, cannot get idle down without stalling [Solved]
 

Hello everyone,
I am working on rebuilding a 1971 C-10 with my dad. We recently put on a new Quadrajet Carb and replaced the points, condenser, coil, and distributor. (here is a link to my post on that):
http://67-72chevytrucks.com/vboard/s....php?p=4123824

Now, the truck turns over beautifully, but we had to set the idle to around 6000rpm! We set the points with a dwell meter, but when I try to back off the idle, it stalls out. I tried adjusting the idle mixture with the screws in the front of the carb, but that didn't have any appreciable change. Any ideas on what we could do to get it down to a normal idle?

Thanks

Re: after new carb, cannot get idle down without stalling
 

could b a vaccume leak

Re: after new carb, cannot get idle down without stalling
 

I have a manual choke that has one vacuum line for the vac assist, then there are two vac inlets on the front of the carburetor that are capped. I have checked and none of them are leaking.

Re: after new carb, cannot get idle down without stalling
 

600 rpm sounds low to me.

Re: after new carb, cannot get idle down without stalling
 

You need to spray WD 40 around the base of the carb and along the intake to see if there is a leak, you will get a change in rpm if there is. As far as idle rpm I don't know what engine you have but 600 is normal for the auto and 700 for the manual trans. on a V8.

Re: after new carb, cannot get idle down without stalling
 

Great! Ill try that next time I am up there. I need to say though, I left a zero off the RPM. It is 6000, not 600. I would be really happy if it was at 600.:)

Re: after new carb, cannot get idle down without stalling
 

Your tach is messed up because a stock engine won't run to 6000 continuously. If it is running that fast you have the throttle stuck open.

Re: after new carb, cannot get idle down without stalling
 

We were using a dwell meter that had an rpm setting, so I dont doubt that I didnt read it correctly. We drove it around yesterday and I was joking that it was cruise control. When we had to stop I would kill the engine since it was paining me to hear it revving that high. Basing the sound on what my Ford ranger 4 cyl. sounds like, it is around 4-5Krpms. When I adjust the idle screw a quarter turn, it will run ok for a few seconds, then just drop and die. I did have it adjusted where it would drop down into what I would call a stall (like an airplane), then it would run back up. This cycled about every 10-15 seconds. This was after adjusting the idle mixture screws.

Re: after new carb, cannot get idle down without stalling
 

The floats could be stuck or adjusted wrong and it is just dumping fuel into the intake. You could try tapping on the front top of the carb to see if it will settle down. Don't hit it hard. You could also look into the carb while it is running and see if fuel is dumping from the bowls.

Re: after new carb, cannot get idle down without stalling
 

What's your initial timing set at?

Re: after new carb, cannot get idle down without stalling
 

If it were me I would take the new carb back and get it replaced with another. I have seen several threads on here where the new rebuilt quadrajet was junk.

Re: after new carb, cannot get idle down without stalling
 

Make sure the intake manifold, carb base, & gasket all match. There are variations in those years & if it all doesn't line up you have a horrible vacuum leak.

Re: after new carb, cannot get idle down without stalling
 

We haven't been able to set the timing yet, since we are revving so high. We have to get to 600RPM for the timing to work.

I think you guys might be onto something there. Thinking more on it, the last time it backfired, I think it blew out the back of the carb. I am going to laugh if that is it. I was telling my dad that it had to be something small. :)

Re: after new carb, cannot get idle down without stalling
 

This is most definitely one of two problems...IMO...

You either have the timing way off...I know it is hard to do, but try loosening the hold down bolt, mark its original location, and then move it gradually to get it to settle out. When I put my edelbrock on my 350 we ran into the same problem and through some trial and error we were able to get it close enough that I could do the adjustment on the carb and then went back and set the timing and then checked the carb adjustment and timing once again...

....OR.....

Your Carb is junk out of the box, this has also been the case with a bunch of Q-junks. They are extremely hard to rebuild, if it is not done properly it will do crazy things like you are speaking of...

Just my .02....

Re: after new carb, cannot get idle down without stalling
 

There is a large opening in the rear of the carb for power brake vacuum outlet. If you are not useing it put a 1/4 in. pipe plug in it.

Re: after new carb, cannot get idle down without stalling
 

Ok let me see if i can follow what you did to this truck, it was running as per other posting, gas was leaking so you bought new carb, then with new carb it backfired and then you started replacing parts,eg...point, dist, cond, etc,,,,,am i close to correct? if so then your problem was the base gasket didnt match the manifold , which caused all your problems, now you will have to start over, pull carb off and match your gaskets to the carb and manifold, then you can go back to troubleshooting one item at a time.hope this helps.

Re: after new carb, cannot get idle down without stalling
 

And that solved this problem. Thanks Wrenchbender!