what is the best jetting combo for a 750 Quick fuel

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fuzzman

fuzzman

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I was wondering what you guys know what the best jetting set up would be for a 408 stroker mild cam and edelbrock air gap manifold. Out of the box the quick fuel has 74 in the front and 80 in the back and the spark plugs ended up completely black. When on the dino we jetted it down to 70 in the front and 74 in the back and it seemed to have a good air fuel reading at cruising RPMs at about 2100 to 2400 and than when you go and idle it down the reading goes off the charts and it smells that way. The next thing I'm going to try is checking my vacuum reading and make sure i have the right size power valve in it. I know that it has a .65 in it right now. I currently put 69 in the front and 75 in the back and the last reading i had on my vacuum was 8 so I'm thinking to try a 45 or a 55 power valve according to Holley's tech page you divide in half for your power valve. My question is do you guys have a combo that you know works and would like to share. thanks in advance
Pat Faley
67 NB 408 Stroker
Peoria IL
 
did anyone try adjusting the idle mixture while it was on the dyno?

changing jets is not going to help the idle if that is where it is rich at........
 
yes they did while it was on the dino. I think the guy running the dino was satisfied with the numbers so thats the way we left it. I took it on a 1000 mile trip this summer and thats when I decided to check the spark plugs when I got back and sure enough they are still show being a little rich by the color of them. You can barely tell that the porcelain is even white. when you drive the car your clothes smell like exhaust fumes. so i know it's still rich.
 
best thing to use is a A/F meter....

the plugs will be colored by the idle and cruise...

so is it rich in idle or cruise
 
which carb is it...

does it have 4 corner Idle?

have you tried to adjust each idle screw in say...1/4 turn at a time....does the engine rpm drop?

are all the screws adjusted the same?
 
First thing, what cam and what is the timing set, initial and total?

Jets will have little and more like no effect on your idle situation.
 
Did you do the recommended base setting?

primary idle screws 1 turn out
secondary idle screws 1/4 turn

Most guys are used to two corner idle and so they run all four idle screws out like on a 2 screw carb. Makes things way too rich.

Are you checking idle vacuum with car in low and foot on brake (ignore if stick).

If you have 8 inches at above, you would want a 4.5 PV
 
70aarcuda said:
which carb is it...

does it have 4 corner Idle?

have you tried to adjust each idle screw in say...1/4 turn at a time....does the engine rpm drop?

are all the screws adjusted the same?
Click to expand...

Yes it has four corner idle screws and they are all ajusted the same about 3/4 of a turn out.
 
LXguy said:
Did you do the recommended base setting?

primary idle screws 1 turn out
secondary idle screws 1/4 turn

Most guys are used to two corner idle and so they run all four idle screws out like on a 2 screw carb. Makes things way too rich.

Are you checking idle vacuum with car in low and foot on brake (ignore if stick).

If you have 8 inches at above, you would want a 4.5 PV
Click to expand...

I have the four corner idle set up with the quick fuel and i didn't know about any base setting of the front set at 1 turn out and the backs set at 1/4 turn out. I will give that a try. right now they are all set the same at 3/4 of a turn out and i did it with a vacuum gauge. I will try it that way this coming weekend and also check my vacuum reading to see if my power valve is to big. What I 've been asking is what jet sizes are used and know that it's the right combination. I think i tried the set up of 70 in the front and 76 in the back and if i remember right the vacuum reading ended up at about 12 or 13 so i figured that the pv was good. Than I tried 69 in the front and 75 in the back the vacuum reading ended up at 8 to 10 so which is the right set up. The other thing is what RPM do you leave it at when you check your vacuum reading with a 4 speed do you check it at 800 or do you kick it up to 1000 and adjust the carb to get the highest reading on the vacuum gauge than adjust it back down to where you want it to be? Than take the reading? What is the correct way? Carb tuning is not my speciality. I need help!
 
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