Holley Carb/squirters+jets ?

Could someone explain to me when it's appropriate to mess with the squirter size, and when it's appropriate to mess with the jets? I'm somewhat confused as to their specific functions. Currently, I have a 750 Holley (flows 930) which has a 42 primary squirter and a 37 secondary (mechanical). Jets are 76/78. Manifold vacuum is 9mmHg. PV is a 4.5 Initial timing is 18 and total is 38, all in by 2800rpm. Car has a mild stumble off the line. Any info appreciated.

im not really sure but to me your jets look fine but your front squirter looks high to me...i have 35's front and back :(

How did you get that vacuum reading? In gear or in park?

1st of all your motor idles on the idle circuit, thats what the air idle screws are for. The PV richen's the system when vacuum drops below a certain point like cruising down the highway and going up a hill so you don't have to use as much pedal. It also richens up the system when you nail it so the jets have time to get the main circuit going. The squirter's help the transistion between going off the idle circuit to the main circuit under normal driving conditions. Now when you nail it a bunch of stuff happens at once.

You have a lot of squirter up front!! :shock:

give me some more info like motor specs, weight, gear ET's etc

Approx. 3200 lbs at the ready. Engine is a '69 383, stock bore and pistons, 906 heads (gasket matched only), 727 trans with 10" 3500 stall TCI super street fighter, full spool with 4.56 gears and 29.5" M/T slicks, Hooker Super Comps with 2" primaries and 3.5" collectors, MSD distrib and a 6AL box. I leave off idle @ 1500 rpm. The stumble is momentary, then picks-up well. Any suggestions? Thanks.

I would try downsizing the squirter on the front and see what happen's. You may be shotting to much fuel at once. What size pump you got, 30cc or 50cc and do you have the hollow screw for the front squirter? Also check your adjustment on the accel pump. Make sure you are just touching the lever at idle. Check the cams on the linkage too to make sure they are adjusted right and not worn out. Move the throttle and make sure you are getting a clean shot of fuel. Look for the obvious stuff first and if everything is fine then I would go to a 35 in the front and see what happens.

yeah!!!,what brett said!!! :roll:
i have 35;s front and back in my 750 and ive gone 12.00's

Thanks guys. I'm going to the strip Sunday for some T&T. I'll follow up whith what I fugure out.

Changed the squirters to a 36 primary and 40 secondary and the off idle stumble was cured. The plugs still read rich though. Gap is .045 Total timing is 38, all in by 2400 rpm. Any suggestions?

What plug you running??

Next time out jet up or down until your MPH drops off, then make a small adjustment up or down in jet size to correct the fall off. Then adjust timing until your ET drops off. Then check plugs again. If still rich go to a hotter plug or quit running race fuel if you are.

I'm using Autolites #AR3933. No on the race gas. Use Sunoco Ultra 94.
Do you think the plugs are too cold? :dontknow:

reference that plug with a champion and I can tell you.

Damn Brett you sound like to know what your talking about. :lol: You going to come down and help me tune a set up this 440 . :?:

I know enough to be dangerous :salut: :salut:

Brett, I cross referenced the autolites AR3933 to NGK 7382, to Champion C59C. What do you think?

I am not familiar with that champion plug but here is a link to it. What you have is a cold plug because that champion is a race plug. Click the link and scroll down until you find the champion number.

http://www.edelbrock.com/automotive/sparkplugs.html


In champion a 9 is cold and a 12 would be a stock plug. I would try aomething in between the 9 and 12 for the $12 it will cost and see what happens. If you are 10.1 comp or higher try a 9 and go a little lean on primary jets.

brett,
i just bought AUTOLITE 63....whatcha think of those??

No clue Mike :scratch: I only know champion and NGK

I would start with stock pv because that 1 is too big for your combo.
Set timing to 35 degrees all in by 2500 rpm.
Make a base run at track.Jet up 2 sizes primary & secondary & make another run.if mph goes down jet down 1 size primary/secondary.check mph again.Repeat until you get highest mph,then reset base carb settings.
I thought my car was running lean until I put it on a chassis dyno & found I had a/f ratio of 11.5 (rich)I was running stock jetting on 850 vac Demon.After a ton of runs & several rd tests.I wound up at 83/85
jetting & a/f ratio of 12.9 straight across.BTW picked up 27rwhp/23ftlb
just from leaning out car.
Rob