Quadrajet going WOT

[ChrisK7und]

Okay, this is going to sound crazy, but I am at a loss for what is happening.  I have a Quadrajet on my ZZ4 350 in my Suburban.  On more than one occasion, a light tap of the throttle etc. causes it to go wide open or close to it.  It happened to my wife once on her way to the store, she left a red light, started into it and it went WOT.  She then got it slowed down by shifting into N and then it was taching out and working the pedal did no good.  They shut the key off and finally got it to shut off.  Upon restarting it WITHOUT touching the pedal, yep....just idled normal.  I thought she was crazy.  I then got in it the other day after coming out of the store, turned it over, it started kinda hard so I feathered the throttle and then BAM.....WOT again in Park.  I shut it down, DIDN'T touch the pedal to see if the same thing had happened.....same thing, fired up to an Idle......I am at a loss!  I can not reproduce this either.  I spent a whole day doing FULL throttle starts, driveway redlines, light throttle etc. NOTHING??  Any ideas?

[429bbf]

im not cliff the expert. but id say you got more than 1 problem. first how does it run when this  doesn't happen? it sounds like your float is to high or the needle and seat stick causing it to over flo slightly .and your throttle plates aren't closing all the way .im talking about the rear ones. its like taking the carb off and feeding it with a spray bottle.the more you spray the faster the engine runs.you may have to wait till the expert (cliff ) responds.

[73 Z28]

A couple of things to I'd check would be the spring  around the secondary throttle shaft to make sure it's not broken and the throttle return springs to make sure one of them is not broken. If these check out ok, you should cycle the throttle with your hand while observing the carb linkage for any binding on both sides of the carb. If all this checks out ok, you should remove the carb and inspect the base gasket for any rubbing against the throttle blades.

Paul

[Cliff Ruggles]

+1 on checking the springs on the secondary throttle shaft.  The outer spring may no longer be wound up with the free end engaged correctly on the linkage......Cliff

[ChrisK7und]

Thanks guys for the ideas.  I have checked the springs on the secondaries and they all look in tact and function just fine when manually opening the secondaries as well as allowing the engine to pull them open etc.  I finally gave up and am trying a new Holley Street Avenger 670 on my ZZ4 after a lot of research.  I am really not into rebuilding this carb or putting time into it.  IF, the Holley doesn't pan out then I will look at ordering a remanufactured QJet from a reliable source etc. 

Thanks again for the ideas....

Chris

[Cliff Ruggles]

I have checked the springs on the secondaries and they all look in tact and function just fine when manually opening the secondaries as well as allowing the engine to pull them open etc.

The double spring arrangement is on the outer portion of the secondary throttle shaft.  It was used to make the secondaries mechanically actuated by the link coming back from the primary side. 

The engine doesn't pull them open, and if it does, the outer spring is broken or not wound correctly.  It gets wound almost a full turn and the free end is help in place by an indent on the linkage at the 1 oclock position.

Don't waste any time or funds on "commercially remanfactured" units, spend it on the one you have now.

The only good sound the late model offshore die cast Holley's make around here, is when they "tink" off the dumpster outside the shop.  The quality on them has dropped to a level so low, we woln't even allow them in the shop......Cliff

[ChrisK7und]

Thanks for your time Cliff, I do appreciate it.  I did take the Edelbrock QJet off and put the Holley on and so far it is running WAY better than my QJet ever did new.  It makes me wonder if the QJet was just not modified for any kind of performance engine even though it was sold that way.  The Holley is working well so far.  However, if I have to go a different route, what do you suggest in the way of rebuilding a QJet?  I tried once and was not happy with my work.  I would prefer to have one built by somebody that knows what they are doing and have it built to work with my ZZ4 350.  It has 10:1 compression with a performance camshaft.  The Quadrajet just never felt like it had any kind of pull when getting into it.  The moment I put the Holley on and took it out I was grinning ear to ear as my ZZ4 has never had the stones like it does now.....

[Cliff Ruggles]

Unless you had an Edelbrock 1910, it was emission calibrated, like all other q-jets. 

Holley carburetors are NOT emission calibrated, and very generous with idle fuel and fuel curves.  This makes them pretty popular and one will almost always see improvement in power production initially.  After they start acting up, and emptying the wallet with high fuel consumption, the "new" wears off, and the owner usually starts looking for a better set-up.  Those designs simply are NOT very fuel  efficient  at light throttle openings (normal driving range), and tend to use a LOT of fuel.  Having at least a dozen places to leak below the fuel level, they also tend to develope problems early in life. 

I went thru that learning curve back in the 1970's, figured out how to go faster with factory carburetors, and NEVER looked back.

Anyhow, once correctly set-up exactly for the application, the Q-jet will run equally as well as the Holley everywhere, and get better fuel economy as well.....Cliff