Author Topic: Rich idle and lean on acceleration  (Read 2771 times)

Offline Ksp3cialK

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Rich idle and lean on acceleration
« on: September 29, 2016, 09:13:26 PM »
Hello, this will be my first post so don't be too harsh :P. Anyway for a little background, this is the first time I've ever ran a carb before as iv converted over from a TBI. I have my reasons, anyway I purchased my quadrajet from a guy locally and threw it on the truck after a rewire and what not.
First impressions, it purred like a kitten and had a smoother idle then the TBI did and had decent part throttle but was lean until i adjusted the APT screw on it and smoothed part throttle out.

At idle it would be around 11-12 afr on my wideband. After tinkering with it, i tried to adjust the idle mixture screws but they didn't do anything. So i backed the RPM set screw so the blades were completely closed and the idle screws started showing changes. I adjusted it to about 20in of vacuum and now Now part throttle is lean and when i accelerate i get a backfire out of the intake.

TLDR. What im getting at here is i have no idea the process i should go about since im so new to carbs. Maybe someone can give me advice on what parts i may need, I feel i need a bigger accelerator pump but not sure about the jets and rods.

Specs:
91 S10 with the 96-00 350 vortech crate motor completely stock.
700R4 trans with shiftkit.
Rear end is a ford 3.73 locker
Performer RPM intake with adapter for spread bore, shortie headers and true dual 2.5 exhaust all the way back.

Qjet is 17080213 108CO GPX. It also has a re-manufacture sticker on the side from 2005.
After dissection, Primary jets are 72, primary metering rods are are 50M and secondaries are DP i think, cant make out what they are very well.

I have locked the secondaries from opening and did a full throttle run and the wideband showed 12-13 if i recall correctly. In theory that should mean the jets are correct for this application rite?
I have also slowly eased it to full throttle with the secondaries unlocked and i never noticed any loud noise or crazy power feel like i keep hearing that qjets are known for. Iv never been able to stab the throttle while driving, it will just bog and go lean on the wideband.

Hopefully this post isn't too all over the place and hard to understand. Im just really not sure what to do next and im tired of dumping money into this truck.
Thank you in advance, Kyle.

Offline Cliff Ruggles

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Re: Rich idle and lean on acceleration
« Reply #1 on: September 30, 2016, 03:07:42 AM »
The first problem is the "remanufactured" sticker.  Those companies have a bad habit of "butchering" up those carbs and installing a generic calibration in them.

Hopefully this isn't the case.  20" vacuum at idle is a lot, how much timing are you running at idle speed?  Is the vacuum advance hooked up?......Cliff

Offline Ksp3cialK

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Re: Rich idle and lean on acceleration
« Reply #2 on: October 03, 2016, 01:47:56 PM »
I believe it was around 18" but i turned the idle set screw to bump it up a little. Also i set the timing to 10 degrees BTDC and yes the vacuum advance is connected to what should be a ported vacuum port.

Iv been to busy to get a chance to warm the truck up and recheck the timing, ill try to do that soon however.

Offline Ksp3cialK

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Re: Rich idle and lean on acceleration
« Reply #3 on: October 11, 2016, 09:44:47 PM »
I checked it with a timing light warmed up at idle and it's at 12 degrees.

Offline Cliff Ruggles

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Re: Rich idle and lean on acceleration
« Reply #4 on: October 14, 2016, 03:44:25 AM »
Probably the best place to start is to get one of our kits so at least it has good parts in it.  I'd also get a new PP spring, we can supply the correct one with the kit.

This will at least make sure the carb is in good working order so you can proceed with testing/tuning.  The jet/rod combo is fine for what you are doing, but this assumes that the carb doesn't have modifications from the remanufacturing process, such as larger airbleeds, idle tubes, etc......Cliff