QJet tuning questions

[Madgyver]

My QJet has been acting like a 2barrel carb this past week. it intermittently stumbles on top of 1st gear (2nd gear np435) but only when I stomp on it aggressively. if I do a gradual acceleration, it will run smooth in the rpms up to next shift.
I've checked fuel filters, timings good, My thought is the transition to the secondaries and the secondary air doors tension adjustments. Not opening when it should and choking the fuel mixture.
Any insights before I start making adjustments..

 

[SteveL]

I was gonna guess that little filter in the carb

 

[73azbronco]

send it to the carb guy, carburetors unlimited, peoria. Or call him, he will answer or call back.

 

[Soylent]

I agree. Call Bruce. He got my quadrajet running great. Fixed several mistakes another shop with similar name did.

 

[gnpenning]

When you operate the throttle at the same speed as stomping on it, look down the throat and see what kind of squirt of fuel you get.

When it comes up to operating temp is it coming off the fast idle cam and allowing the stop for the secondaries to clear?

Hard to describe tension online for the secondaries. Try and tell us what you find when you push down as best you can.

 

[Madgyver]

When you operate the throttle at the same speed as stomping on it, look down the throat and see what kind of squirt of fuel you get.

When it comes up to operating temp is it coming off the fast idle cam and allowing the stop for the secondaries to clear?

Hard to describe tension online for the secondaries. Try and tell us what you find when you push down as best you can.

There is no stop for secondaries.
I'll be trying the tension spring adjustments today since I have no work calls coming in lately. It's tedious to do because to test it I need go on open road to stomp on the throttle. 1/8 turn at a time.

 

[gnpenning]

@Madgyver , I'm sorry, I probably wasn't very clear. Take the air cleaner off, operate the throttle linkage by hand from under the hood with the engine off. Just use the same speed as if you were on the road and stepping on it. You want to see what kind of flow your accelerator pump is putting out.

On the passenger side down low where the throttle shaft comes threw is where the lock out will be. It basically there to keep the secondaries from opening when the choke is on. At one time it was a green color. Don't know if it's still the same color after all these years.. If needed I can take a picture for you.

 

[nvrstuk]

That's why I asked the question I did on your FB post Mad.

Have you got the same vacuum you had before the problems started?

Have you ever adj the adjustment screw on the rear pass side underneath? This adjusts when the secondaries open and how fast. Little bitty tiny screw

 

[bronco italiano]

Mad,
FB has a real nice rochester quadrajet carburetors group.
Real nice members on the site.

 

[Madgyver]

That's why I asked the question I did on your FB post Mad.

Have you got the same vacuum you had before the problems started?

Have you ever adj the adjustment screw on the rear pass side underneath? This adjusts when the secondaries open and how fast. Little bitty tiny screw

I've been working on it. A little at a time.
I finally got it to get better but the stumples still exist, not as much.
I adjusted it the wrong direction and almost stalled on the highway after I punched it. it would get up to 3500-4000 in gear and it stumbled so bad that it got to a point too where I had to clutch it and let motor catch up. I couldn't tell if it was flooding or starving.
now after getting it adjusted the CCW I noticed a difference. But it still exists, not as bad.

 

[73azbronco]

fuel pressure, quality of fuel?

 

[Madgyver]

fuel pressure, quality of fuel?

I think it's the fuel pump going out. Got stuck again this evening that put me in a bad predicament on the freeway. Got out of it and drove off. next stop and I looked at the fuel pump and it didn't look good. Nursed it home on town roads keeping it below 2000. I'll be swapping it out tomorrow.
It didn't look bad when I first checked when opening up fuel filter in front of it.
Carter electric. I have a spare in my tool box. Process of elimination.

 

[gnpenning]

Pressure and volume test and you will know for sure. You will be taking the line off anyway.

 

[Madgyver]

Okay, looks like a failing fuel pump was the root of my QJet issues. Swapped the old fuel pump for new one and now I can stomp on it again..
Yay! It's back..

 

[73azbronco]

surprising how easy part first...

 

[mrdrnac]

Glad you found the issue Mad. The Carter pumps are pretty bulletproof but they can go bad, I guess? About 8 years ago my Bronco's 30 year old Carter fuel pump started squealing after I tried to start it after sitting for 6 months. So I bought a new one to replace it and by the time the new one arrived the old one was working just like it always had. New one is still my {on Board) spare and never had to change the pump.

 

[Madgyver]

Pressure and volume test and you will know for sure. You will be taking the line off anyway.

I put a psi gauge on the output side of the old pump and it showed 5 psi with intermittent drops to 3 psi.