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New Quadrajet bogs when accelerating from idle.

cameronsaddress

cameronsaddress

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Hey guys, I'm moving this post from an old thread about other issues.

I just installed a new qjet on my 350 and it bogs when coming off idle. It is bad enough to kill the engine sometimes.

I vacuum tuned the idle mix screws to highest vacuum. They are about 4.5 turns from seat.

No vacuum leaks


Could it be a timing issue? What else could I check?



Thanks
 
4.5 turns from seated on the idle mixture screws is way too much...I know you said no vaccum leaks but it sounds like you have a serious one.
What is your vaccum reading?
 
The way I did it was with a vacuum gauge, I turned the screws out until I pulled the most vacuum then turned them in a qtr turn.
 
Ported vacuum for dizzy is on right when looking from front of truck, right?
 
Wow, must be a busy bunch...

The ported vacuum will pull very little signal at idle, if the throttle blades are closed...check it with a vacuum guage.

Did I give you a link for some timing and carb tuning?
 
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A bog is generally caused by a lean condition, too much air, not enough fuel, check fuel pressure and volume, and be sure the secondary flap adjustment is not too loose, that is a start.
 
wrong, ported vacuum is above the primary throttle blades. Manifold vacuum is below the blades.
 
Greg Ducato said:
be sure the secondary flap adjustment is not too loose, that is a start.
Click to expand...

Try this, if you are looking at the carb from the front of the truck the adjustment is on the rear left.

One thing you can try without messing with the adjustment is to slide a spring down the air cleaner stud and use a wing nut to tighten it down and then try driving. If it doesnt bog anymore then you need to adjust the secondaries. If it still bogs then you dont need to adjust them.
 
That spring to hold down the secondaries was a great idea!

With the secondaries held shut, it is less of a bog now and more of a hesitation. from a dead stop, when I step on the gas, i hear air intake, and then the rpms go down and then up and then the truck responds a second or so late.

I have leaned out the idle mixture screws as far as they will go without killing the engine, and it still bogs. I have richened them up way passed good vacuum and everywhere in between, but it still has the issue.

Where else should I be looking?


Could you shoot me that tuning guide link too?


Thanks!!
 
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Qjet links:

http://www.lbfun.com/warehouse/tech_info/fuel%20&%20intake/Q-Jet%20Problems.pdf

http://www.lbfun.com/warehouse/tech_info/fuel & intake/Q-Jet Tuning Paper.pdf

QJet%20FrontVacuumFitings.jpg
 
Crazy, it works from my pc, but my iphone throws a server error...

thanks again
 
Hey guys,
I ended up giving the dizzy more advance and it has almost completely cleared up. It still has a small but annoying bog at low acceleration. If I step into it aggressively, no bog.

Could too much advance cause a bog? I also found that manifold vacuum to the vac advance seems to help ( instead of ported)?

I also notice a slow engine start when the engine is hot. Starter kicks over fine but engine sounds like it is barely getting gas. If I give it throttle it recovers. Hope this helps.

Any other things to check?
 
How old is the dizzy?

It seems like when guys are chasing issues like this it ends up being a balance between carb tuning and ignition tuning.

If the dizzy is old, there's a chance that the advance weights are sticking or not working right. A lot of times you can rebuild it with new advance weights and different advance springs (light to heavy types) to change how quickly the advance happens. Sometimes a "too heavy" spring will prevent the timing from advancing... So a lighter spring will help.

-G
 
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