Quadrajet help

[gscherer78ta]

I have a Qjet, 17057262, installed on my Pontiac 400, bored .030" over with a Lunati Voodoo street cam and '68 #46 Poncho heads with 1.96/1.77 valves and 73CC chambers, dual exhaust. A street set up that should run around 350hp/400tq. The Carb has feed this combination for nearly a year and turned 14 sec 1/4 times and many autocross runs.

Earlier this summer I started getting a slight hesitation at lower rpms, slight hesitation meaning it didn't feel like it was getting off the line as quickly. When investigating this I came upon some little bits of charcoal canister that the carb sucked up. I cleaned off the bits and cleaned some of the little passages and put the carb back on and the slight hesitation became a stumble at lower rpms. I completely disassembled the carb and blew cleaner through all the passages and then ran thin wire through all the passages- the idle down channels, air bleeds, idle air, main circuit fuel, accelerator pump passages, pull over enrichment passages, secondary air bleeds and fuel. If there was a hole I cleaned it but I did not soak it in cleaner. I still have the stumble.

The car runs ok once the secondaries kick in and it starts and idles and cruises great under light and medium throttle. Only under 3000rpm and heavy throttle does it stumble. I have #73 jets and #43 rods with .035" idle down channels and .063" air bleeds.

A long history there, thanks for sticking with me. The reason I'm posting here is to see if anyone in this group has gone through this experience or something similar and if you would share what you did to get things working again. I've already heard that I just need to go with Holley, so, that suggestions as already been tendered.

Thanks in advance.

Greg

[mikewoods]

I don't have any suggestions, but I have a similar issue in my car running a Qjet. Its almost like the secondaries don't open quickly enough and the car stumbles until the air/fuel mixture "catches up". Thanks for posting, I look forward to the responses.

[gscherer78ta]

Mike,

I agree with that assessment. I have removed the choke pull off to test whether allowing the secondaries to come in right away would help- and it didn't. I also increased the float level- thinking that under lower vacuum operation but, before the secondaries open, the POE might add some gas to help it. That seemed to make a slight improvement.

[Shaker455]

I have a Qjet, 17057262, installed on my Pontiac 400, bored .030" over with a Lunati Voodoo street cam and '68 #46 Poncho heads with 1.96/1.77 valves and 73CC chambers, dual exhaust. A street set up that should run around 350hp/400tq. The Carb has feed this combination for nearly a year and turned 14 sec 1/4 times and many autocross runs.

Earlier this summer I started getting a slight hesitation at lower rpms, slight hesitation meaning it didn't feel like it was getting off the line as quickly. When investigating this I came upon some little bits of charcoal canister that the carb sucked up. I cleaned off the bits and cleaned some of the little passages and put the carb back on and the slight hesitation became a stumble at lower rpms. I completely disassembled the carb and blew cleaner through all the passages and then ran thin wire through all the passages- the idle down channels, air bleeds, idle air, main circuit fuel, accelerator pump passages, pull over enrichment passages, secondary air bleeds and fuel. If there was a hole I cleaned it but I did not soak it in cleaner. I still have the stumble.

The car runs ok once the secondaries kick in and it starts and idles and cruises great under light and medium throttle. Only under 3000rpm and heavy throttle does it stumble. I have #73 jets and #43 rods with .035" idle down channels and .063" air bleeds.

A long history there, thanks for sticking with me. The reason I'm posting here is to see if anyone in this group has gone through this experience or something similar and if you would share what you did to get things working again. I've already heard that I just need to go with Holley, so, that suggestions as already been tendered.

Thanks in advance.

Greg

Greg, check your fuel pressure & do you have a blue alcohol resistant accel pump inside the carb?

[gscherer78ta]

Greg, check your fuel pressure & do you have a blue alcohol resistant accel pump inside the carb?

I haven't checked the fuel pressure yet- good tip. What kind of pressure range is acceptable?

The accel pump is a blue one from Cliff Ruggles- as are the needle and seat, jets and rods and the float.

[Shaker455]

6.5 psi

[Nothingface5384]

Shoot this guy a call/email
He knows his **** more them anyone I know of now that John Osborne doesn't do q jets anymore


Https://www.google.com/url?sa=t&sour...K75E7r4Qq_EbZQ

[gscherer78ta]

Thanks for the suggestions. Does anyone know of some other Qjet experts that they can suggest? Especially if they are in the DFW, TX area.

To update: I completely disassembled the carb and had it cleaned, soaked and blown dry. The engine fired right away after I assembled it and idled very smoothly. It still has the stumble when heavy throttle is applied at lower rpms.

Cliff told me that my .100" main air bleeds are too large and that I need only .070" so I can experiment with that. Otherwise, I'm at a complete loss.

[reschke18]

Since your carb once ran well, I doubt anything major needs to be re-engineered. Check the accelerator pump. The job of the pump is to give an extra shot of fuel when throttle position changes. This is to overcome the stumble that would occur until the air speed increases. The ethanol that is in every drop of pump gas these days will dry out and shrink the rubbers and seals in our carb, so replace your accelerator pump. You need a very strong squirt, nothing half hearted. Even if it seems good, it may not be enough.

[Shaker455]

Thanks for the suggestions. Does anyone know of some other Qjet experts that they can suggest? Especially if they are in the DFW, TX area.

To update: I completely disassembled the carb and had it cleaned, soaked and blown dry. The engine fired right away after I assembled it and idled very smoothly. It still has the stumble when heavy throttle is applied at lower rpms.

Cliff told me that my .100" main air bleeds are too large and that I need only .070" so I can experiment with that. Otherwise, I'm at a complete loss.

PM sent

[gscherer78ta]

PM sent

Got your PM Shaker. Thank you. I have a few more things to check out that I can do, I may be giving you a call after that.



Greg

[gscherer78ta]

I just wanted to circle back on this thread in case anyone in the future has issues with their Qjet. I took mine to Larry Wells in Weatherford, TX and he rebuilt it and now the car is running great! Larry is a great guy and does great work and gets things done quickly. He finished in 4 days. Carbs are all he does.

I pressed him to tell me what he did and he plays what he does close to the vest and just said that he re-did some things in it and put it together the way he thinks they should be done. I can't argue with the results.

PM me if you need his number.

[gscherer78ta]

Another Update to this thread. Carb seems to running great and I'm enjoying my TA again. I've been to a couple events recently and I felt like the TA did as well as it ever has...

[ATTACH=CONFIG]103697[/ATTACH

[mikewoods]

Glad to hear the car is running well! I'll be PMing you shortly for Larry's contact information.

[MonzaRacer]

Making sure adjustable part throttle is tunable also. This allows tuning at cruise for surging and cruise lean out.