Quadrajet gurus *update*

[gone huntin]

I bought a Quadrajet from pull a part that looked really clean and has a remanufactured sticker on it. I got it on my '75 Suburban (fresh 350 w/a Melling MC-1 cam) and it fired right up, runs great. I have two issues though, it loads up at idle in gear, but not park, and the secondaries aren't opening at all. The vacum can in front of the choke (electric) that is attached by linkage to the secondary butterfly is supplied vacum to keep the butterfly closed. Even at wot it won't open, tried while stationary and while driving. I'm ok working on Holleys, but I'm in the dark on Qjets.

 

[mdm365]

I bought a Quadrajet from pull a part that looked really clean and has a remanufactured sticker on it. I got it on my '75 Suburban (fresh 350 w/a Melling MC-1 cam) and it fired right up, runs great. I have two issues though, it loads up at idle in gear, but not park, and the secondaries aren't opening at all. The vacum can in front of the choke (electric) that is attached by linkage to the secondary butterfly is supplied vacum to keep the butterfly closed. Even at wot it won't open, tried while stationary and while driving. I'm ok working on Holleys, but I'm in the dark on Qjets.

As far as it loading up in gear and not in park(never seen that) If in fact it's loading up it would do it at any time.

I would look for a vacuum leak and or low idle.How about the timming seeing that there is cam involved?As for as the secondaries not opening,Is the choke working? The high idle adjustment also will effect it.
I always remove the lock out lever on all performance q-jets.

If the choke is not working it will keep the secondary lock out engaged seen in the pics below.The vacuum can should pull the linkage forward to allow the top butter flies to open to allow more air in as the secondaries do open.
There is also an adjustment for these under the air horn seen in the last pic.Adjusting this will make it easy or harder to open and it's one of these things that's a pain in the a$$ unless you have done it a time or two on the truck.

Hope this helps a little

Mike

 

[Blue85]

What do you mean by loading up? If it's mis-firing, it could be a vacuum leak or an ignition problem. What is the idle speed? Also, if the spark timing is wrong, it can puff black smoke and run bad just like the carb was too rich. Stalling in gear happens as much from too little fuel as from too much. You do lose vacuum in gear - it's possible that it would work better with a ported vacuum advance. What is the timing in Park and in gear?

As for the secondaries, all you can do is make sure the little lockout swings away when the engine is warmed up all the way. And with the enginge warmed up and off, make sure the throttle linkage works to turn the secondary throttle shaft. The top air flapper will not open unless there is an actual load on the engine, so you can't check that when the vehicle is sitting.

 

[dyeager535]

Only a slight correction...vacuum breaks on the Q-jet secondaries hold them shut, and allow opening at a measured rate (as the vacuum drops) to keep the air valve from "fluttering" as engine vacuum changes, to try and prevent the engine from bogging.

I would agree about the choke though....if not adjusted correctly the secondary throttle plates will never open, and the vacuum break doesn't matter.

 

[gone huntin]

Well, what I mean by loading up is that it seems to stumble just a bit at idle when in gear and if you put it back in park and rev it there is a puff of black smoke. It never does this when idling in park. It may be idle speed, it's a bit low, it's about 500rpm in drive. As far as the secondaries there is no contact between the pimary throttle linkage and the secondary throttle linkage. There is a lever sticking up on the primary throttle shaft that links via rod to the secondary throttle shaft, but it doesn't touch anything. I can manually push it back and the secondaries open and you hear the definate sound of a four barrel. Thanks for all of the replies too guys. As far as timing and other settings, they're fine. I had no problems with the Holley 600 on it other than it dies on rough terrain and hills.

 

[gone huntin]

In the world of auto mechanics there is a term used for simple repairs made complex by the person performing said repair, K.I.S.S. is this term. Those of you that have used this know what I mean. The 4 barrel not opening was caused by a kickdown cable being too tight not letting the linkage go past half way.

I drove it to work today and it's really loading up while being driven. After an 8 mile drive it was really chugging at stops. I put it in park when I got to work and revved it up a few times and got alot of black smoke out of the exhaust. I'm gonna pull it back off tommorrow and take it apart to see if the well plugs are leaking and gonna put a kit in it.