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I haven't wired up the wideband yet. It likely will be done next week.

Till then, any of you fellas that want to chime in with a suggestion or two would be helpful.

5.3 milled 706 heads
220/224 .581 .581
Dual plane
1 7/8 primary headers
2500 stall th400 3800 lbs 3:89 rear

Timing is 12/18/33
Quickfuel q750

74 primary jets, 84 secondary jets, a 4.5 primary power valve. The air bleeds are .070 idle and .033 high speed. The squiters are .031.


Above 2k when I jump on the throttle it bogs rich and catches up in the 48-5k rpm range.

94 s dime

iTrader: (10)

Exact carb I'm running with the same issues lol

ZONES89RS

iTrader: (25)

Sounds like the secondaries need to come down. You been reading plugs or what? With my 6.0 and Trex i was running jetting like that. I would think 72/76 may be a better starting point for the jetting to begin with. Up the timing 20* initial and all in to 34 by 2000 RPM. See what it looks like then.

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Carbon deposits on plugs. Rich. Someone also suggested switching to a .036 high speed air bleed.

I really tried to locate some similar situations on the carb database. I was really disappointed. It seems like everyone else bought a Vic Jr.

3pedals

iTrader: (3)

How do you know it's bogging rich? - the carbon deposits on the plugs? How are you executing your plug checks? Plug checks don't really tell you anything about part throttle conditions unless you can hold the exact condition for a sustained period of time - then kill it, and pull the plug for a read. Almost impossible.

What vacuum does this engine pull at idle? And at 2000rpm?
I'm betting a 8.5 pv will help. The 4.5 you have opens at too low of vacuum.
Get your wideband on it ASAP ! Best thing you can do to help diagnose the carb tune.

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3 pedals,
When I jump on it hard it sounds like I'm pouring fuel in with a Dixie cup. When I slowly accelerate it seems much better. The plugs have 38 miles on them and they are dirty black and dry. When I set idle, the vacuum resulted in 19 and smooth at idle to a grand. I don't know higher rpm range. I need to weld a bung for the wideband when I get a day off. Thanks.

3pedals

iTrader: (3)

You wrote timing 12/18/33
What rpms are those at?

Pop N Wood

iTrader: (1)

I agree with the guys above. Seems like awfully big jets and low PV trip point. You have a fair sized cam but still, the big jets might be masking the power valve coming in too late. By the time you give it enough throttle to kick in the PV you are too rich.

I wouldn't touch an air bleed until you get the base mixture right (stick with jets and IFR), and you are only guessing on mixture until you get a wideband on there.

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My timing is actually:
000:15
300:22
2000:29
5600:29
6200:27

1 bar MAP enabled.

3pedals

iTrader: (3)

Ok , your timing is not too far off. But I just re read that your idle vacuum is 19"? If so you really should have a much higher pv open point. 8.5 minimum but probably higher. I am also remembering way back when I ran a 750 Holley and it had 70-80 front and rear jets. That's not crazy different, but could be a factor. I'm not familiar with the brand of carb your running, it may need slightly more jet because of the way it's metering blocks are setup.

I'd put an 8.5 pv in to start, and drop jets down to 70 -80. Then hurry up and get your O2 bung welded in !!
Don't mess with air bleeds untill you have the rest figured out pretty well, and you start chasing perfection with the wideband! Lol

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Thanks for your time 3peds, pops and zone. I am having one hell of a workweek, trust me. guys, otherwise this wideband would be done already. 3peds, if my 19 vacuum seems high, I assume my being 12 feet above sea level increases that a bit.

The q750 is described here: http://www.quickfueltechnology.com/f...talog-2013.pdf

I actually purchased it over a Pro Systems at the rec of some guys on this site. Jegs has it.
http://www.jegs.com/i/Quick-Fuel/793/Q-750/10002/-1

My part number is Q-750
Description on catalog for this model says High Flow Main Body
QFTTM die cast main aluminum main body is tumble polished and feature recessed air bleed cavities for improved air flow. Venturi are die cast to exacting tolerances to provide excellent throttle response and maximum wide open air flow. Screw-in air bleeds enable fine tuning of both idle and high speed circuits. Q-Series carburetors and their aluminum construction weigh considerably less than most competitors.
Billet Metering Blocks
CNC-machined with multiple emulsion channels provides more precise fuel metering improving throttle response and a more uniform fuel curve. Billet metering blocks feature changeable idle feed and power valve restrictions.
See page 23 for Metering Blocks.
Billet Throttle Body
QFTTM throttle bodies are CNC-machined to strict tolerances and provide exceptional precision and strength. Slabbed, TeflonTM coated throttle shafts are assembled with TeflonTM ribbons for years of smooth operation. See page 19 for Billet Throttle Body kits.
Adjustable Secondaries
All QFTTM mechanical secondary carburetors have an adjustable secondary idle speed bracket; this allows fine tuning of the secondary throttle position for improved idle adjustability. Mechanical secondary carburetors also feature a QuickLinkTM system that alters the secondary opening rate by simply changing the provided links. 40%, 60%, or 1:1 opening rates are included. All QFTTM vacuum secondary carburetors feature QFTTM adjustable QuickSetTM diaphragm housing. Adjusting the rate of opening on vacuum carburetors is as simple as turning a screw. See page 21 for QuickSetTM Adjustable Secondary Housing.
QFTTM Fuel Bowl
QFTTM aluminum fuel bowl is unique combining strength with a significant weight reduction. All Q-Series fuel bowls feature dual threaded fuel inlets and dual sight glasses. Dedicated floats for specific applications ensure optimum carburetor performance characteristics without additional upgrades required. QFTTM fuel bowls are assigned U.S. patent number D543,999 & D543,555.

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I ordered the 70s jet kit, some air bleeds, and an 8.5 pv from jegs. By the time it arrives the innovate will be installed and THEN I will be bugging the **** out of you all. Thanks again.

94 s dime

iTrader: (10)

We upped te squirters on mine last night and seemed to help tremendously, have some jet work left to do but it's close!

RabidStreetRacer

iTrader: (1)

Whats the weight on your car, heavier vehicles tend to do better with a vac-secondary over mechanical. Power valve recommendation is half of vacuum at idle.
From Holley:
The purpose of a power valve is for it to add the needed extra fuel when you are under wide open throttle. It is not intended to be an enrichment circuit during normal throttle cruising.

If you are lean or rich during normal driving conditions, you need to tune the jets, not the power valve.

The reason you check the vacuum at idle and take that reading and divide it in half, is so you do not have a power valve that will open at idle as this will cause an excessively rich mixture at idle. . Under WOT the vacuum of the engine will drop to 0 or near 0 and the power valve will then open adding the extra fuel needed during WOT.

3pedals

iTrader: (3)

I dont agree with deciding on a powervalve by dividing idle vac in half, but it can get you close. I beleive it should be slightly lower than cruise speed/load vacuum readings so that it will open and enrichen moderate acceleration at part throttle.
The powervalve does not flow ANY fuel through the idle system, and has no effect on idle what-so-ever. - Unless the powervalve is torn or damaged, then it can leak fuel into the intake.

newschool72

iTrader: (12)

Im no pro by any stretch on carb tuning, but I have done all my own stuff with holleys for years.
I always found a BOG was a lean condition, as in the fuel metering couldnt keep up with the secondaries opening all at once. I have used the pump cam and squirters to adjust that on all my carbs and always get good results. Then MPH at the big end with jets till I max out.
Ive also gone on the lighter end with power valves. I dont want any enrichment till Im hammer down and near zero vacuum.
Like I said earlier, Im no pro but this technique has worked very well for me. 94 s dime seems to be coming to a conclusion like mine be upping his squirter size. I bet a more aggressive pump cam would finish his issues, instead of jetting. Then look for max MPH at the track to adjust jets.

RabidStreetRacer

iTrader: (1)

I agree with you on the power valve selection, but for getting started it is holleys general rule to start out with 1/2 the amount of vacuum at idle in gear with an automatic. Then get a vacuum reading while driving to better determine a size. I'm sure you know a ton more that me about the carbs. I just recently had this issue with my carb and found my power valve was too big and was running real rich. Thought I'd offer how I narrowed down the problem after reading through Holley for awhile.

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So I welded in the bung this morning for the wideband. I've got a ne vacuum gauge, a QFT 70-80 jet kit, an .036 hs bleed and an 8.5 power valve sitting on the workbench waiting for me to get a few hours to fiddle with it. I still need to wire the gauge and hide it in the dash. You guys have been a tremendous help so far.

Sunday morning I am also fabbing and welding it the ride tech front shock kit. I have been limping around on bags with no shocks for a week or so. Not so safe.

Thanks again.

Jeff Smith

iTrader: (44)

Same thing I have ls2 carbed, been black/dry on plugs..Last nite I work on Ls2 Carbed and i dont know where the jet of the carbed..I ll look thru youtube..
Pix>

Good inform here..

RabidStreetRacer

iTrader: (1)

I was able to get alot of help tuning by looking on youtube. Holley has alot of their adjustment and tuning videos on there.