i know it impusible to nail the exact jet size without playing with the carb but, in a atempt to get a little better perfomance a swaped the jet from a 71 to 66(primary side) and it seems to be perform pretty soggy. becuse i striped the threds on the secondry side, i'm only running on two barels(soon to be fixed)it ran much faster with the 71s feeding the motor than the 66s. i think i went to lean. the guy at the speed shop said i should be running 68 jets primary side of things. i would like your guys opinion on what aprox jet size to run hers my combo

350, 8.5:1 comp ratio, clened up heads.224,224 with 450(in) 461(ex) cam. i have headers and a edelbrock Perf RPM

any suggestion would be helpful

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when the green flag drops the bull$hit stops

350,performer RPM intake ,650dp, 700r4, headers, 3inch exhast

 

Everyone's motor is different. You need to use an O2 sensor in your exhaust and monitor it while you drive. You'll have to use seat of the pants and the O2 sensor readings to continue to make educated guesses on jet changes.

Sounds like you need to fix your carb, first!

 

First find out what the factory jet sizes are supposed to be from the list number on the air horn of the choke tower. I can't remember what the elevation is of Winnipeg. I think you're still pretty low. You can drop 1 jet size for every 2000 feet in elevation. Other than that it's almost a trial and error method for determining the proper jets.

You can do it at the race track by watching your MPH. Carbs are factory set to sea level so most need to be richened up. Go up 2 jet sizes at a time and see if the MPH changes in the 1/4 mile. When the MPH drops, go back to the last jet size then start on the secondaries and do the same thing.

My 383 engine ran best with 87 primary and 91 secondary in an 850 DP

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Stephen's racing page

87 IROC-Z Pro ET Bracket Race Car and knocking on the SuperPro ET class
383 stroker (carbed) with double hump cast iron heads and pump gas
LS6 Big Block buildup now in progress

Best results before the engine blew up
Best ET on a time slip: 11.857
Best corrected ET: 11.163
Best MPH on a time slip: 117.87
Best corrected MPH: 126.10
Best 60 foot: 1.662

Racing at 3500 feet elevation but most race days it's over 5000 feet density altitude!

Member of the Calgary Drag Racing Association

 

I'm running 68s or 69s on my Vortec headed 350 (Perf RPM intake, 218/224 cam, Holley 750, headers, etc). The 68s-69s are about perfect for my engine according to my air/fuel ratio meter. After you get something that feels right, drive for a bit and pull a couple plugs out. You want a nice tan coloration on the plugs, white = lean and black = rich.

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Ray87Z
-Vortec headed 350.
86 IROC w/ a cammed 305 TPI.
Formerly Ray86IROC.
www.inter-scape.com/Ray

 

how long would you think it takes to get a new set of plugs 'tuned'-colored in before you read them?
I've got about 30 miles/60 minutes run-time on a new set of Autolites and wouldn't want to 'jump-the-gun' on pulling them?
Duffster_Camaro@hotmail.com


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Duffster (age 31)
BEAT DOWN HARD 88' Camaro Sport Coupe,
1978 Caprice Classic 305 motor havin'(WITH NO COMPUTER),84' 700R4 Tranny usin', 84' Z-28 Nose clip wearin',
84' Z-28 Hood covered,
AND THE TIRES:
245/60-16 Firehawk SS20 on Firbird rim(1-passenger rear),
235/55-15 BF Goodrich's on CompTA's on Z28 rims(2-on front),
235/60-16 Pirelli P600 w/a curb check or 3 also on Firebird rim(1-drivers rear),
REAR HATCH MASTER OF ALL!!!
Duffster_Camaro@HOTMAIL.COM
Owner of the Camaro 0 out of 10 Third-genners approve of, no longer part of the non-existent Iowa crew.

 

My Demon 750 came out with 76/83's....do you think it would benefit from adding or playing with bigger jets?

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350 4 bolt main, Speed-O-Motive 383 stroker kit, re-sized rods ground for clearance,Hypereutectic pistons,9.8:1 compression,HPC Coated RPM intake, Speed Demon 750 cfm carb,World Products Sportsman II heads,2.02/1.60 valves, K-Motion springs, Comp Cam 1.6 roller rockers, Lunati adv.292/230@.050 with .512 lift,Crane pushrods,Proform HEI and MSD6A box,HPC coated 1 5/8 headers, 2.5" exhaust with 40 series mufflers,TH350 with B&M 3000 stall, Powertrax NoSlip Locker, 4.11 gears.

 

Polecat- in a word..... you never know until you try. They mighta gotten it nailed perfectly from the factory and they might not. Don't expect miracles from a carb that's already tuned for max performance from the word go, but I have tuned almost 1/2 a second out of many "economy" QJets.

Gold85- don't play with the jetting until you get the secondaries working. I don't know if you totally disconnected the secondary throttlw linkage (sounds like it) but you don't want to tune like that. The mixtures from the two sides of the carb produce an "average" A/F ratio when they are both open so tuning one side of the carb at a time is kinda meaningless. Also, at higher RPMs manifold vacuum is probably rising and closing the power valve if you are running only on the primaries- totally throwing off you tuning efforts.


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94 Firebird Formula M6- No options but Z rated tires. No mods over $10. 13.5@105.
79 Malibu "beater" w/junkyard 400 SBC, tweaked QJet 4bbl, finally a decent set of heads, a few other tricks. A maddening 13.000001 @ 108 on the motor with little traction. No nitrous runs with the new heads yet.
Grandma's old 78 Malibu (33K miles!) soon to have the powertrain from the 79 put in it.

"One of the last remaining QJet tuners on Planet Earth!"