Qjet troubleshoot - Team Camaro Tech
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post #1 of 23 (permalink) Old Apr 23rd, 11, 02:11 PM Thread Starter
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Qjet troubleshoot

So, in the name of "fuel economy" I traded my DP holley on my 68 for a 73 Q-jet.

so far economy has increased significantly, but the problem is that the holley made the car a tire shredder... which is lacking on the qjet, also my secondaries keep bogging on me constantly.

The transfer slots are adjusted to "square" accel pump arm is on the inner-most spring running 73 jets, 43 rods (IIRC) air flap is set to 7/8 turn past zero tension.

Also the Pull over enrichment discharge holes are above the airflap if that really does make a difference

motor specs; 355 10:1 compression, 290 degrees duration .501 lift on the cam, 3000 stall convertor.
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post #2 of 23 (permalink) Old Apr 23rd, 11, 02:18 PM
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Bog on the secondaries means the air valve spring needs more tension.


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post #3 of 23 (permalink) Old Apr 23rd, 11, 05:54 PM
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Re: qjet troubleshoot

been years since i actually touched one, but if memory serves correctly, the choke pull off vacuum pot also controls secondary air valve opening rate. it could be bad, of course we usually tossed that linkage and adjusted spring tension much like a thermoquad.
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post #4 of 23 (permalink) Old Apr 23rd, 11, 06:58 PM
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Re: qjet troubleshoot

Quote:
Originally Posted by ap68 View Post
air flap is set to 7/8 turn past zero tension.
As suggested by both posters, add more spring tension in 1/4 turns until bog vanishes.

Engine should have plenty of initial advance, whatever is deemed necessary to prevent the starter from shrugging when hot, and with engine idling, you should be able to go to WOT and eleventy bizillion rpm's in about 3 microseconds, maybe sooner.

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post #5 of 23 (permalink) Old Apr 23rd, 11, 09:30 PM Thread Starter
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Re: qjet troubleshoot

Timing's still set where it was before I pulled the holley, about 14 initial 32 total.

I timed the release on the choke pullover, about 1.32 seconds, I've got another I timed at 2.35 I suppose that would probably be a better choice to run.
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post #6 of 23 (permalink) Old Apr 24th, 11, 06:34 AM
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Re: qjet troubleshoot

All the choke pull-off does is prevent the sec opening while the choke is on.
See the stop on pass die of airhorn?
Once choke is heated up and choke plate is open, the sec 's should be allowed to open.
You may need to try another hole in the accel pump linkage, either too short of shot or not enough, but only after adjusting sec air valve tension.
I have had one Q-jet needing 1.75 turns from zero tension to remove the bog.

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post #7 of 23 (permalink) Old Apr 27th, 11, 08:31 PM Thread Starter
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Re: Qjet troubleshoot

well, the issue I'm really having is from idle to WFO (wide follicking open) the car just really doesn't shred tire like the holley did. I've increased idle air bleeds, and discharge port size.

I believe I'm running 74/44 jets and rods

Also the other question I have is the Hanger for the rods doesn't ride on the plastic cam that actuates the secondary rods, seems like the airflap opens 10-15 degrees before the rods move. secondary hanger is an M
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post #8 of 23 (permalink) Old Apr 27th, 11, 08:56 PM
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Re: Qjet troubleshoot

You have to get the engine to work with the primaries first. Disconnect the secondaries and tune tO make the engine respond to WOT first. Then tune the secondaries.
Secondary air valve comes on by engine demand.

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post #9 of 23 (permalink) Old Apr 27th, 11, 09:28 PM Thread Starter
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Re: Qjet troubleshoot

okay will try that tuning in the morning... my biggest experience with quads has basically been tossing them for a holley so far. but man, I love this thing so far.
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post #10 of 23 (permalink) Old Apr 27th, 11, 11:12 PM
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Re: Qjet troubleshoot

There is only one way to tune a carb..be it a holley, Qjet, or IMPCO...whatever
A O2 data logger..
There is a thread a while back, someone 'green' at tuning using an inovate unit...step by step...exellent results, power and economy.

I have just dropped a new carb on my engine...worn the old one out...and gone Qjet base plate... rsults are dramatic...worth every penny spending on the data logger...will pay for itself within 6 to 9 months.

My Spelling is not incorrect...it is creative

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post #11 of 23 (permalink) Old Apr 28th, 11, 12:29 AM Thread Starter
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Re: Qjet troubleshoot

well steps theres always an 02 gauge on my dash, consistantly this carb stays in the 12:1 to 14:1 range, that's where me not "getting it" is coming from. i'm starting to wonder if I'm getting full range of motion with the quad that I was getting from the holley.
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post #12 of 23 (permalink) Old Apr 28th, 11, 12:46 AM
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Re: Qjet troubleshoot

look here at these sites!!!!
http://vetteworks.tripod.com/qjet.htm
http://www.442.com/tech/rochester.html


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post #13 of 23 (permalink) Old Apr 28th, 11, 01:09 AM
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Re: Qjet troubleshoot

in your application--a qjet will run as good as a holley--i think your on the right track with cam for sec rods-i have seen many where that shaft or cam is wore down-hold the butterfly shut and see if cam mes alittle or loose
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post #14 of 23 (permalink) Old Apr 28th, 11, 05:30 PM
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Re: Qjet troubleshoot

Quote:
well steps theres always an 02 gauge on my dash,
A gauge is not good enough to tune well..it doesnt have enough response.
I just posted this in another thread
https://www.camaros.net/forums/showpo...55&postcount=5

Quote:
Also what is good idle air/fuel and cruise. Right now idle is at about 13.1 and cruise is fat at about 12.1. Wot is 12.5 to 1. Help?????

When using a O2 data logger..caution.
Make sure all your HT leads , plugs etc are in top condition and everything is firing 100%.
A slight , undetectable misfire will come up as a lean condition, because of increase in O2 levels...a miss fire maybe under load (plug gaps) only.
This is where a data logger using O2, a MAP (vac) , advance, and maybe throttle postion...then reveiw logs later will pick up stuff like that.
Not being 100% sure all is correct can get u and the engine into a lot of trouble.
Do not rely just on a O2 gauge for tuning
A vac leak will generally give incorrect readings right across the board.

Ideal AFR is 14.7.
One goes for either ecomony mixtures or power mixtures
Economy:
Idle around 15 to 15.5...a leaner mixture u can run more idle advance...and smoother idle.
Cruise 30 mph same as idle
Cruise 60 mph will drop due to slightly heavier loads (wind etc) 14.7 to 15.0
Light load up a slope 14.5 to 15.0
WoT 13 to 13.5
Power:
Idle basically as above, 15 to 15.5
30 mph cruise 14.6 to 15.0
60 mph cruise 14.4 to 14.7
WoT 11.5 to 12.5.

Be 100% sure the O2 sensor calibration is correct.....in fresh air should read 20.95%
If the O2 sensor has been positioned correct, not in a low spot of the exhaust, over night check will show about 20.9% as a quick check....If not located in a good spot, HC gases are heavier, tend to hang around and the O2 will read lower than 20.9%

Use a logger for tuning, do not use a gauge...they are not quick enough response to give accurate reading for tuning purposes.

If you data is faulty, everything falls apart....Caution.
If correct, the results are dramatic.

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post #15 of 23 (permalink) Old Apr 28th, 11, 11:47 PM Thread Starter
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Re: Qjet troubleshoot

well, I put the holley back on the car earlier today, and that's the way this car should run, tons and tons of power and loads of fun, but still horrible gas mileage.

Checked the plastic cam on the qjet secondaries, looks good, gonna take it from there in the morning.
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