I've been tinkering with the CC Q-Jet to tackle that lousy off-idle bog and just can't seem to totally get rid of it. I'm wondering if the secondaries still aren't opening fast enough.
It's not a "choking-off" kind of bog, it just feels like it's only at 3/8 throttle when I put it to the floor-only off idle though, like for a launch. It lasts no more than about 1 second and then it gets rippin'. If I roll into it, it's fine.
I've got the spring tension lightened up, running CK rods on a G hanger, timing's bumped up to 8*. M/C solenoid, and IAB adjusted as per spec, float slightly lower than spec (3/32", if memory serves me)
Think I need to try Edelbrock's servo to get rid of this problem?

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D.R. Stevens
1984 Trans Am 305HO L69
all the usual external/free mods, original engine
1991 Firebird 305 L03
2 free mods and a K&N,
otherwise stock

[This message has been edited by eightTfourTA (edited November 03, 2001).]

 

If you're making the air valve open faster, you're moving in the direction of increasing the "bog", not getting rid of it. It's caused specifically by the air valve opening too fast and dumping in more air than the fuel flow can catch up with, and thereby making the engine run lean just at the time it most needs some extra enrichment, which is what causes the lean "bog".

Lightening the AV spring tension obviously will also add to the tendency to "bog".

There's alot of misunderstanding and misinformation out there about how these carbs work. If the AV opens too slowly, what you get is no "bog", but also a slow ramp-up of power. If the AV opens too fast, you get the secondary tip-in "bog" or flat spot, but then it takes off afterwards.

Don't forget, the Q-Jet has no secondary accelerator pump as such; all it has is the shot of fuel it gets from the 2 wells in between the fuel bowl and the sec bores. Make sure that system is working properly.

Having the fuel level set low also aggravates the "bog"; the lower the bowl level, the greater distance fuel has to be raised to begin discharging into the bores, which takes time, which adds to the "bog".

Stock MCS and IAB adjustment will definitely make the car run lean all the time on the primaries; those specs are designed for emissions, not performance. And if the engine is already on the ragged edge of leanness while it's on the primaries, then when it gets that extra sudden dump of un-fueled air when the AV opens too soon, you're guaranteed to make the "bog" worse.

My stock L69 carb with the AV tension set to 5/8 turn will almost chirp the tires if I stand on it at 2000 RPM. This is with the MCS rich stop set about 1 turn out from stock, the lean stop about at spec, and the IAB set for max idle vacuum; stock bowl level, and stock vacuum dashpots.

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"So many Mustangs, so little time..."
ICON Motorsports

[This message has been edited by RB83L69 (edited November 04, 2001).]

 

RB, what you're saying is you've got the AV 5/8 turn from 0 tension, or 5/8 from stock?
Also, did you leave the accel pump stock?

 

5/8 from 0

Stock accel pump

------------------
"So many Mustangs, so little time..."
ICON Motorsports

 

You might want to also upgrade your secondary rods to L-69 spec "DR" rods with a "B" hanger. The difference in throttle response is dramatic.

 

Damon, hi. I remember you telling me that the DR rods would be the best, but when I went to order them from Carbs Unlimited they didn't have the DR's, so that's why I got the CK's. I did, however, buy both a G and a B hanger.
In your opinion, can I make these CK's work good with the B hanger or would the DR's be better on that particular hanger?

As far as other carb aspects, I put in an A/F gauge to get an idea of what's happening with the enrichment. It fluctuates irradically between the 14.7 mark and the extreme Lean side during normal driving. I don't see full enrichment during WOT, either, but the proper rod/hanger combo should take care of that hopefully.
So i'm wondering, is the computer overcorrecting for a rich condition, or do I just need to adjust this carb as per RB's instructions?
Thanks for any help guys. In the past i've known just enough to keep one of these functioning, but this is the first time i've gotten serious about dialing everything in just right.

 

You get the DR's from GM (yes, they are still available).