Had it With Quadrajet Holley Replacement
Thread Starter
Instructor
Joined: Feb 2011
Posts: 234
Likes: 15
Had it With Quadrajet Holley Replacement
I really need help. I had this Quadrajet rebuilt last year and now if you floor the gass pedal the car hesitates like crazy. Like as if too much gas. But if you put the gas pedal half way down all is good. Should I give up on Quadrajet and get a Holley? Whicb Holley do you recommend? Was looking for good economy, but got tk have the performance and reliability. What do you recommend?
Thanks.
Thanks.
Safety Car
Joined: Mar 2007
Posts: 3,652
Likes: 49
From: Bridgewater nj
The secondary's are coming in too fast. There is an adjustment on the passenger side rear of the carb. It takes a small Allen key to adjust the spring tension of the secondary flaps. They should barely open while reving it in park. Maybe a 1/4 inch they should pop open. If they are opening more than that, it will bog! It's hard to explain but YouTube will show you how to do it! It's easy
Race Director
Joined: Jan 2000
Posts: 12,399
Likes: 247
From: San Jose CA
It's likely the secondary air-valve windup as mentioned above. You actually have to put a small screwdriver on a knurled **** to keep the spring from unwinding, and then loosen the allen screw. If you simply loosen the allen screw, the spring tension will cause the spring and knurled **** to unwind completely.
Here's a view of the bottom side of a Pontiac airhorn (VERY similar to the M4M on a 75):
You can see the allen screw, air-valve shaft and spring in this photo.
The slot you need to hold with the small slotted screwdriver is just below the groove that the choke pull-off link rides in, towards the rear of the groove. Tighten it up in 1/8 turn increments until your stumble improves.
Alternately, it could be too lean of a calibration (primary or secondary), but this is a good starting point.
Realistically, this is set at a starting point of ~7/8 turn past 0-load, but it's easier to learn this with the air horn off.
Good luck!
Here's a view of the bottom side of a Pontiac airhorn (VERY similar to the M4M on a 75):
You can see the allen screw, air-valve shaft and spring in this photo.
The slot you need to hold with the small slotted screwdriver is just below the groove that the choke pull-off link rides in, towards the rear of the groove. Tighten it up in 1/8 turn increments until your stumble improves.
Alternately, it could be too lean of a calibration (primary or secondary), but this is a good starting point.
Realistically, this is set at a starting point of ~7/8 turn past 0-load, but it's easier to learn this with the air horn off.
Good luck!
Le Mans Master
Joined: Oct 2010
Posts: 6,938
Likes: 848
From: melbourne florida
2023 C3 of the Year Finalist - Modified
the quadra jet isn't a bad carburetor but it takes a lot of tinkering, and adjusting . holley makes a quadrajet replacement that i have used on several cars and it performs well and bolts to the stock manifold. either one would serve you well
Racer
Joined: Nov 2004
Posts: 485
Likes: 1
From: Oakville ON
secondary air valve adjustment
It's likely the secondary air-valve windup as mentioned above. Tighten it up in 1/8 turn increments until your stumble improves.
Alternately, it could be too lean of a calibration (primary or secondary), but this is a good starting point.
Realistically, this is set at a starting point of ~7/8 turn past 0-load, but it's easier to learn this with the air horn off.
Good luck!
Alternately, it could be too lean of a calibration (primary or secondary), but this is a good starting point.
Realistically, this is set at a starting point of ~7/8 turn past 0-load, but it's easier to learn this with the air horn off.
Good luck!
Personally, I like mine a bit looser as long as it doesn't bog (the car "comes on" the secondaries sooner).
Also note that Lars says most rebuilt carbs are bug***ed up by the rebuild shops so you may have other problems (but it sounds like it runs okay other than the bog. Good luck.
Melting Slicks
Joined: Mar 2009
Posts: 3,126
Likes: 15
Sounds more like the accelerator pump has failed. Was the carb. rebuilt with one of the blue ethanol proof acc. pump cups? Remove air cleaner with engine off and move carb. linkage while looking into the top of the carb.. There should be a twin shot of liquid fuel that hit the venturis. Just what I would check first. mike...
Safety Car
Joined: Apr 2006
Posts: 4,057
Likes: 421
From: BC
Sounds more like the accelerator pump has failed. Was the carb. rebuilt with one of the blue ethanol proof acc. pump cups? Remove air cleaner with engine off and move carb. linkage while looking into the top of the carb.. There should be a twin shot of liquid fuel that hit the venturis. Just what I would check first. mike...
If it was the secondaries and it didn't bog before there is no reason for it to bog now. Check the acc pump.
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Thread Starter
Instructor
Joined: Feb 2011
Posts: 234
Likes: 15
Ok I just noticed that when the secondary flaps open and close they don't close back all the way shut because the rod sec meters do not go all the way back down. Would this cause the hesitation when the gas pedal is floored?
Thank you all for the education, really thank you!
Thank you all for the education, really thank you!
Le Mans Master
Joined: Mar 2008
Posts: 5,948
Likes: 72
From: Oxford MA-----You just lost the game!!!!
Ok I just noticed that when the secondary flaps open and close they don't close back all the way shut because the rod sec meters do not go all the way back down. Would this cause the hesitation when the gas pedal is floored?
Thank you all for the education, really thank you!
Thank you all for the education, really thank you!
Scott
Race Director
Joined: Jan 2000
Posts: 12,399
Likes: 247
From: San Jose CA
That said, not sure if he meant "it was rebuilt and had problems since then" or "it was rebuilt, and 1 year later it's bogging".
The wording suggests the latter, but it can be easy to type up the wrong intent...
Le Mans Master
Joined: Mar 2008
Posts: 5,948
Likes: 72
From: Oxford MA-----You just lost the game!!!!
Thanks, I should have been able to figure that one out for myself, huh?
Well, if the secondary air flaps won't close all the way, they are hanging up on something, obviously. You should be able to figure it out by playing around with it. Accelerator pump is an easy check, too, get back to us.
Scott
Well, if the secondary air flaps won't close all the way, they are hanging up on something, obviously. You should be able to figure it out by playing around with it. Accelerator pump is an easy check, too, get back to us.
Scott
Safety Car
Joined: Mar 2007
Posts: 3,652
Likes: 49
From: Bridgewater nj
If you can close them by hand, then the adjustment is way too loose and the Allen key needs tightening but if they're suck open .....
On the drivers side there's a pin that holds the secondary's closed while the choke is still engaged. When the choke is fully open the pin swivels out of the way and let's them open but it can also hold them open a little if the choke closes a little before they return.
On the drivers side there's a pin that holds the secondary's closed while the choke is still engaged. When the choke is fully open the pin swivels out of the way and let's them open but it can also hold them open a little if the choke closes a little before they return.
Le Mans Master
Joined: Mar 2008
Posts: 5,948
Likes: 72
From: Oxford MA-----You just lost the game!!!!
If you can close them by hand, then the adjustment is way too loose and the Allen key needs tightening but if they're suck open .....
On the drivers side there's a pin that holds the secondary's closed while the choke is still engaged. When the choke is fully open the pin swivels out of the way and let's them open but it can also hold them open a little if the choke closes a little before they return.
On the drivers side there's a pin that holds the secondary's closed while the choke is still engaged. When the choke is fully open the pin swivels out of the way and let's them open but it can also hold them open a little if the choke closes a little before they return.
Scott
Safety Car
Joined: Mar 2007
Posts: 3,652
Likes: 49
From: Bridgewater nj
Le Mans Master
Joined: Mar 2008
Posts: 5,948
Likes: 72
From: Oxford MA-----You just lost the game!!!!
Anyway, wherever it is, you are right, it's worth checking out.Scott
Race Director
Joined: Jan 2000
Posts: 12,399
Likes: 247
From: San Jose CA
It's on the passenger (right) side of the QJet. Same side as the choke and choke pulloffs.
Apologize for the state of the engine bay in that photo - before I went through a major cleanup.
Apologize for the state of the engine bay in that photo - before I went through a major cleanup.