after new carb, cannot get idle down without stalling - The 1947 - Present Chevrolet & GMC Truck Message Board Network

colbyclay · 12-20-2010, 10:50 AM

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

cdowns · 12-20-2010, 11:14 AM

could b a vaccume leak

colbyclay · 12-20-2010, 11:22 AM

Quote:

Originally Posted by cdowns

could b a vacuum leak

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.

Sinister · 12-20-2010, 12:10 PM

600 rpm sounds low to me.

haysonj · 12-20-2010, 12:21 PM

Quote:

Originally Posted by colbyclay

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.

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.

colbyclay · 12-20-2010, 12:53 PM

Quote:

Originally Posted by haysonj

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.

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.

haysonj · 12-20-2010, 01:07 PM

Quote:

Originally Posted by colbyclay

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.

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.

colbyclay · 12-20-2010, 01:16 PM

Quote:

Originally Posted by haysonj

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.

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.

haysonj · 12-20-2010, 02:31 PM

Quote:

Originally Posted by colbyclay

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.

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.

*C-10 simplex* · 12-20-2010, 03:51 PM

What's your initial timing set at?

kevmic28 · 12-20-2010, 04:20 PM

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.

Wrenchbender Ret · 12-20-2010, 04:50 PM

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.

colbyclay · 12-21-2010, 09:55 AM

Quote:

Originally Posted by C-10 simplex

What's your initial timing set at?

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.

Quote:

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.

Quote:

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.

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.

tex_waco_usmc · 12-21-2010, 10:06 AM

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....

Wrenchbender Ret · 12-21-2010, 04:54 PM

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.

dadsworktruck · 12-21-2010, 05:50 PM

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.

colbyclay · 01-04-2011, 02:14 PM

Quote:

Originally Posted by Wrenchbender Ret

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.

And that solved this problem. Thanks Wrenchbender!

12-20-2010, 10:50 AM	#1
colbyclay Registered User Join Date: Aug 2010 Location: San Antonio TX Posts: 15	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 Last edited by colbyclay; 01-04-2011 at 02:14 PM. Reason: added details, changed RPMs.

12-20-2010, 11:14 AM	#2
cdowns Senior Member Join Date: Jan 2003 Location: daytonabeach Posts: 22,956	Re: after new carb, cannot get idle down without stalling could b a vaccume leak __________________ 71c-10 350/2004r/4:11 lowered3/4 longbed/dead by hurricane MEANING OF DEATH::::: SOMEBODY ELSE GETS YOUR STUFF DONT BELIEVE EVERYTHING YOU THINK TAKE MY ADVISE;I DON'T USE IT ANYWAY

12-20-2010, 12:10 PM	#4
Sinister Between Trucks... Join Date: Mar 2002 Location: Los Angeles, CA. Posts: 3,830	Re: after new carb, cannot get idle down without stalling 600 rpm sounds low to me. __________________ Beat it to fit, Paint it to match...

12-20-2010, 03:51 PM	#10
C-10 simplex Account Suspended Join Date: Dec 2008 Location: indisclosed Posts: 1,515	Re: after new carb, cannot get idle down without stalling What's your initial timing set at?

12-20-2010, 04:20 PM	#11
kevmic28 Registered User Join Date: Jun 2009 Location: Arlington Texas Posts: 602	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. __________________ 1970 GMC truck 1988 Harley 1200 Sportster

12-20-2010, 04:50 PM	#12
Wrenchbender Ret Registered User Join Date: Oct 2005 Location: Overland Park, Ks. Posts: 5,229	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.

12-21-2010, 10:06 AM	#14
tex_waco_usmc Project Heaven in my 67!!! Join Date: Jan 2009 Location: Bosqueville, TX Posts: 899	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....

12-21-2010, 04:54 PM	#15
Wrenchbender Ret Registered User Join Date: Oct 2005 Location: Overland Park, Ks. Posts: 5,229	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.

12-21-2010, 05:50 PM	#16
dadsworktruck Registered User Join Date: Jul 2009 Location: blacksburg,s.c. Posts: 155	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.



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