Stumbles when hot
Thread Starter
Racer
Joined: Jan 2003
Posts: 397
Likes: 0
From: Morganton GA
Stumbles when hot
I am having a problem with my '71. I had this problem before changing intake, carb and fuel lines. My old Qjet started leaking like a seive and needed replacement.
The issue is when it is cold, it runs great and has tons more response and power than with the old Qjet and stock manifold. But, once I reach operating temperature, it starts to stumble and hardly run when opening the throttle. I don't want to start another path of changing a ton of stuff, just finished that with the carb. Hopefully there are some ideas out there.
I have the stock fuel pump and a Mallory unilite distributor that has been converted from dual points to electronic pickup.
The issue is when it is cold, it runs great and has tons more response and power than with the old Qjet and stock manifold. But, once I reach operating temperature, it starts to stumble and hardly run when opening the throttle. I don't want to start another path of changing a ton of stuff, just finished that with the carb. Hopefully there are some ideas out there.
I have the stock fuel pump and a Mallory unilite distributor that has been converted from dual points to electronic pickup.
Melting Slicks
Joined: Nov 2001
Posts: 2,668
Likes: 43
From: Eastern US XX
Originally Posted by MYBLU71
I am having a problem with my '71. I had this problem before changing intake, carb and fuel lines. My old Qjet started leaking like a seive and needed replacement.
The issue is when it is cold, it runs great and has tons more response and power than with the old Qjet and stock manifold. But, once I reach operating temperature, it starts to stumble and hardly run when opening the throttle. I don't want to start another path of changing a ton of stuff, just finished that with the carb. Hopefully there are some ideas out there.
I have the stock fuel pump and a Mallory unilite distributor that has been converted from dual points to electronic pickup.
The issue is when it is cold, it runs great and has tons more response and power than with the old Qjet and stock manifold. But, once I reach operating temperature, it starts to stumble and hardly run when opening the throttle. I don't want to start another path of changing a ton of stuff, just finished that with the carb. Hopefully there are some ideas out there.
I have the stock fuel pump and a Mallory unilite distributor that has been converted from dual points to electronic pickup.
Drifting
Joined: Jul 1999
Posts: 1,542
Likes: 43
From: Plano TX
I can only speak from experience with GM HEI electronic ignitions. When the HEI module fails it usually runs fine when cold then does exactcly as you say when hot. Seems it can no longer fire the mixture. I found this by using electronic cool spray on the module after it starting running rough and it solved the problem. Change the $20 module and issue was solved. I have had the same issue on other HEI equiped cars.
Fro HEIs the pickup and module are separate. When the module fails it will usually limp home but when the pickup fails it will not run.
The Mallory might be failing in the same way. I think it's one unit for the mallory (pickup and module in one).
You could try points if not too easy to change and see if it runs better as a test.
Fro HEIs the pickup and module are separate. When the module fails it will usually limp home but when the pickup fails it will not run.
The Mallory might be failing in the same way. I think it's one unit for the mallory (pickup and module in one).
You could try points if not too easy to change and see if it runs better as a test.
Thread Starter
Racer
Joined: Jan 2003
Posts: 397
Likes: 0
From: Morganton GA
Thanks Guys,
That was my suspicion. I just didn't want to throw money at something that I didn't have a clue what was causing it. I will check on that piece and see what happens and let everyone know.
That was my suspicion. I just didn't want to throw money at something that I didn't have a clue what was causing it. I will check on that piece and see what happens and let everyone know.
Thread Starter
Racer
Joined: Jan 2003
Posts: 397
Likes: 0
From: Morganton GA
Well, guys I replaced the electronic module in the distributor and still had the same problem. I then bought a Mr. Gasket kit that had 3 plates and gaskets and I installed two of each and no more problem. Thanks for all of your input.
Race Director
Joined: Sep 2002
Posts: 10,362
Likes: 5
From: San Diego - Deep Within The State of CONFUSION!
Originally Posted by MYBLU71
I am having a problem with my '71. I had this problem before changing intake, carb and fuel lines. My old Qjet started leaking like a seive and needed replacement.
The issue is when it is cold, it runs great and has tons more response and power than with the old Qjet and stock manifold. But, once I reach operating temperature, it starts to stumble and hardly run when opening the throttle. I don't want to start another path of changing a ton of stuff, just finished that with the carb. Hopefully there are some ideas out there.
I have the stock fuel pump and a Mallory unilite distributor that has been converted from dual points to electronic pickup.
The issue is when it is cold, it runs great and has tons more response and power than with the old Qjet and stock manifold. But, once I reach operating temperature, it starts to stumble and hardly run when opening the throttle. I don't want to start another path of changing a ton of stuff, just finished that with the carb. Hopefully there are some ideas out there.
I have the stock fuel pump and a Mallory unilite distributor that has been converted from dual points to electronic pickup.
Drifting
Joined: Sep 2004
Posts: 1,532
Likes: 4
From: Fairview Heights Illinois, near Saint Louis MO, STL C3 Shark
What abouta vacuum leak? The choke would come on when cold, but the vacuum leak allowed more air to come get in. Once warm, the choke went off, and let lots of air in, it was just waaay too lean of mixture?
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