Carb tuning

powershift · May 25, 2008

I have a 79 Z with a 355 12.5- 1 comp ratio G.M. double hump heads 2.02 valves roller cam 278/525 strip dom intake 750 proform carb, MSD 6AL muncie m21 2.20 first gear 4.56 rear gears.engine acts like it's running out of fuel while in 4th at cruising speeds. Jet sizes are 70 mains 81 sec. Plugs looked lean but when adjustusted mixture screws runs rich at idle.Would going up in jet size and leaning out mixture screws help? Tired of pulling plugs and playing with mixture screws!! Please give some advice. Thanks

HarleyD67 · May 25, 2008

yes try jetting it at 72/84

trmnatr · May 26, 2008

I have a combo close to yours on the street in a 327 over on Team Chevelle in my '70 chevelle, I run 83/83 jets with a .036" high speed bleed

13:1 compression
260/268 @.050 .630/.630 110° lobe seperation
Dart 215cc heads

'70 chevelle with dad driving weighin at 375 it has runs low 12's @ 110.04-112mph, It will go 11.90's - With our old 327 set up it will go 10.90's but it is not streetable, its on the edge now - we run a 4200stall

The 10.90 set up is 283/291 @.050 106° lobe center with 6,000rpm stall - my current smaller cam and converter i can drive

I can post a video if you would like

powershift · May 27, 2008

83 jets pri and sec? I have jetted dominators carbs like that but have never heard of tuning a 750 like that,seems like the engine would load up at idle. What is your timing set at, locked in at 40 degrees? Thanks

trmnatr · May 27, 2008

powershift said:
83 jets pri and sec? I have jetted dominators carbs like that but have never heard of tuning a 750 like that,seems like the engine would load up at idle. What is your timing set at, locked in at 40 degrees? Thanks

13:1 327, Dart 215cc heads, 260/268 @.050 .630/.630 110° lobe center installed @106° ICL, single plane, 750 with 83/83 with .059" idle air bleeds and .036" high speed air bleeds with .045" squirters - I use a BG750

TH400 automatic with transbrake and 4,200rpm stall, 5.38 gears, full dressed '70 chevelle with 375 pound driver

Click on link to see video fron Nostalgia event last year, click on trmnatr video
http://chevelledotcom.com//video/

Shift light set to come on at 7,600rpm, by time we factor driver delay and time to shift we are pulling gears at 7,900-8,000rpm, On this run it ran 7,600rpm past the lights but the dang converter was locking up too much causing it to pull the engine down and it sounded like it was going flat but it was loaded as we were shifting higher than we ran past the lights - It will run 11.90's as is - It pulls to 7,800rpm

powershift · May 31, 2008

I installed 74 pri 82 sec jets and it runs alot better. I also adjusted the ecellerator pump to get a little bigger shot of fuel. It still seems a little lean.I thinking about going up to 76 pri and 84 sec.Rear power valve is blocked off . i have heard of guys blocking off the primary side power valve, What would be the results of doing that?

Carb tuning

powershift

HarleyD67

trmnatr

powershift

trmnatr

powershift

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