[1971 Chevelle]

I rebuilt my Quadrajet to Cliff's specs for my car(Trans-am). I believe the float is set right. Its got a Carter 120gph fuel pump. New jets and rods. New accel. pump, basically all new inside.
When I first started driving it would buck when trying to cruise at light throttle. I turned to APT screw out until that quit.
The problem I am having is with the Secondaries. If I drive along at 30 in first gear it will spin the tires like crazy, but then if I shift into second and get back on it, it bogs. Or if I try to punch it in 2nd or 3rd gear at say 2500rpm it will bog but it sounds like the secondaries are opened, then when it gets up around 4 or 5K it will pull like a freight train. The same happens in 4th at 3000rpm.

Would the spring that controls the butterflies in the air horn need tightened more? Or would it be the choke pull off the lets them open, Cliff gave me a new pull-off in the kit. Any suggestions? It gets very expensive testing this at $4.30/gal for premium. Fun, But expensive.

 

[gnicholson]

how big is the restriction on the choke pull off? what 2nd rods? have you done any mods to the pull over circuit at the air valve

 

[1971 Chevelle]

The secondary rods were turned on Cliff's lathe, not sure of the size. As for mods at the pull over circuit you have me confused.

 

[gnicholson]

some people call it a secondary accel. pump. small discharge holes either just above or below the air valve depending on carb. it helps to enlarge the discharge size if it bogs on initial opening of the sec.. start with your airvalve spring adjusted to3/4 turn after contact and go an 1/8 turn at a time tighter. what rod and hanger do you have? the pull off might have to large of a restriction. raising the rods with a higher hanger might help as would a richer rod. tell me what you have and ill try to help

 

[1971 Chevelle]

Thanks, I'll have to check on everything. Cliff ask everything about my car and sent me parts to match it. Are you talking about the holes just above the the butterflies in the front of the secondaries, if so I didn't touch those.

 

[gnicholson]

those are the ones. all the things i mentioned affect performance during sec opening

 

[gnicholson]

also , make sure the rod from the choke p/o has a very small amount of clearance when vacuum is applied to the p/o. sometimes this rod is bent to long and allows the airvalve to move before it can be controlled by the p/o

 

[1971 Chevelle]

The spring on the secondary might not be adjusted right. Also, what size hole should the discharge pump hole be opened too? Would a large restriction allow it to open to fast? It probably opens twice as fast as the one that came on the carb stock. Thanks.

 

[gnicholson]

a large opening on the pull off will allow it to open too fast. usually on the nipple where the vacuum hose goes. if the hole has been opened up to the tube i.d. the you will have no dampening effect. the discharge holes for the airvalve can be enlarged .002 or .003 to help pull a little more fuel like an accel pump nozzle in a holley for instance:beers:

 

[SWHEATON]

Yup,your exprieincing the good old QUADRABOG that cause the the upper sec air valve being ad too lose resulting it openign too quickly.

Then the sec gets a quick rush of air but the secondary fuel hasnt caugh up yet thus leaing out the secondary mxi making it bog untill the fuel finsally get there.

Simply tighten the upper sec spring a 1/4 turn and try it it out ,if it still bogs now tighten it in only 1/8 turn segments just untill the bog stops but the sec are still opeing fairy quickly and thats the sweet spot.

Good luck.

Scott

 

[Unclepennybags]

I rebuilt my Quadrajet to Cliff's specs for my car(Trans-am). I believe the float is set right. Its got a Carter 120gph fuel pump. New jets and rods. New accel. pump, basically all new inside.
When I first started driving it would buck when trying to cruise at light throttle. I turned to APT screw out until that quit.
The problem I am having is with the Secondaries. If I drive along at 30 in first gear it will spin the tires like crazy, but then if I shift into second and get back on it, it bogs. Or if I try to punch it in 2nd or 3rd gear at say 2500rpm it will bog but it sounds like the secondaries are opened, then when it gets up around 4 or 5K it will pull like a freight train. The same happens in 4th at 3000rpm.

Would the spring that controls the butterflies in the air horn need tightened more? Or would it be the choke pull off the lets them open, Cliff gave me a new pull-off in the kit. Any suggestions? It gets very expensive testing this at $4.30/gal for premium. Fun, But expensive.

Luke,

Two possibilities come to mind. Either the secondary air valve is too loose, or your choke pulloff is working too quickly.

The spring that controls the air valve is located on the shaft that holds what looks like choke plates for the secondaries. Get a small allen wrench and loosen the lock down bolt which is upside down. Before you loosen it though, get a small screwdriver to hold the tension adjusting screw which is visible from the passenger side near the secondary air valve shaft. Loosen the lock down screw while holding the tension screw. Loosen the tension screw until the secondary air valve has zero tension on it. Now tighten in 3/4 turn. That should give you a good baseline. Test drive the car. If it still bogs, replace your choke-pulloff.

If neither of the above fixes works, you either have the wrong secondary metering rods, hanger, or a vacuum leak on the secondary side.


Mike

 

[1971 Chevelle]

Thanks for the input guys, I think I only tightened the screw about 3/8 or 1/2 a turn when I rebuilt it.:clonk: Should I try putting the old pull-off back on?

 

[SWHEATON]

Luke,you need to try adj the upper sec valve,it usually only takes a few tweaks to get it correct and from my experience 9 of 10 times doing just that will fix a quadrajet secondary bog issue.

Scott