When adjusting the pump shooter size on a holley, how can I tell whether to go up or down in the size? I can't tell if my 390 needs a quick shot of a longer duration.

 

are you having a stumble on acceleration? stock squirter is a #25, increase to a 30 and see if it improves, usually noticable on a hard acceleration of reving up the engine in park, motor will have a very slight hesitation, I still have stock accelerator pump cam on mine, just increased the squirter size

Hope this helps!!

 

I actually have a summit carb but it's set up like a holley and uses holley parts. The current squirter size is 35. Vehicle is a 75 F100 4x4 with a 390/t18 4 speed and 4.56 or 4.88 gears on 36" tires.

I think it'd be considered a stumble on acceleration. If I try to take off to fast it will fall flat then slowly get up to power gain unless I let off. If you need to know anything else let me know!

 

hold throttle to full open, engine OFF!!! check the gap between accelerator pump arm and adjusting rod, possible to much clearance, alot of people think to tighten the adjuster will give a "better" shot of fuel, not the case, may be out of adjustment. 35 squirter is huge, go down a couple of numbers, rechecked your air fuel mixture screws at idle. Is this a new crb for your truck? or is this a new problem that just started happening?

 

It's a problem I've had since I've gotten the truck 2 years ago. It used to have an edelbrock on it that wasn't tuned whatsoever and it was even worse with that. It's at least tolerable now. I've made steps forwards and backwards with adjustments. I am currently using the orange cam in the #1 slot and it seems to work the best. When I used the blue cam it seemed to do better but would hesitate if I opened the throttle too much to quick while cruising. Are you sure I don't want to go up in squirter size?

 

I think the largest they make is a 37? if it is like a holley, have you removed primary bowl to check power valve? if valve is blown, you will have fuel on the power valve side where it mates to the main body of carb, some holleys have an accelerator pump transfer tube that is just above the power valve, made out of copper-tube cylinder in shape, hollow in the center to transfer fuel from accelerator pump into the main body to the squirter, it is sealed on either end with "o" ring so fuel will only transfer thru the tube, possible fuel is bypassing causing your problem. Do you have a vaccumn guage to hook up to manifold vaccumn when adjusting carb? should be 12-15 inches of vacumn in park
check the above items, correct if necessary, also check float levels on level ground running, pull sight plug, when adjusted correctly, you will need to push on fender to slightly rock the truck and fuel should just dribble out of the bowl,
hope this helps, let us know how it goes!!

 

Unless he has a real high preformance engine shouldnt a vac gauge reading at idle be more like 19-21 hg? I have read that and my fairly stock 360 with a Holley 4160 can be adjusted to that.

 

I forget exactly what the largest nozzle size is but it's in the .05's. The floats are set correctly as well. My vacuum reading is at 17. I have a single plain intake and I've been told that it needs a big shot from idle.

 

The reason you may need a bigger squirter size is because of your gear ratio. Holley recommends larger squirters for higher numerical gear ratios. Also, what accelerator pump are you running? You will probably have to bump up to a 50cc if you have a 37 or larger squirter. The largest squirter in my kit is a 52 and you shouldn't be anywhere close to that.

As mentioned above, I would check the clearance on the pump arm at wide open throttle with a .015" feeler gauge. I found that mine wasn't quite set right even from the factory. Then play with the squirter size

When I did my tinkering, you could tell the difference between an off idle stumble and the engine bogging down from too much of a shot and I am no carb tuning expert. 37 was good for me and 40 was teetering on the edge. Once I hit 43, it was definitely noticeable that it was too much of a shot so I bumped back down to 37 since that seemed to give me the best throttle response and no bogging on acceleration. I also found out that the pump cam can make a noticeable difference in how the engine behaved. I found out that for my application a brown cam with a linear graph shape worked better than the cams with aggressive graph curves.

Here is a link to some info about my combination I gave to someone else:

https://www.ford-trucks.com/forums/1...l#post12102410

 

Yea I've tried the brown cam before but only with the current .035 jets. I'll get the jet kit after work today and install the next size up and try the brown cam again and see what happens. I do remember that cam being better for getting on the throttle. I'll let you know how it does.

 

I run a Holley 750 on top of a Weiand Stealth intake on my 460 with a 31 tube-stye nozzle and the green cam and get great throttle response in gear and neutral. I tried a 50cc pump but ended up with a lot of black smoke from the exhaust and a worse stumble than I started out with.

A 50cc pump might solve your problem with the single-plane intake but I would exhaust all my efforts making sure the stock 30cc pump doesn't work since you will drop $60 for the 50cc kit

Have you tried changing the position of the cam in relation to the retainer screw? Most cams have two holes, with exception of the brown cam (one) and the pink cam (three). Position one produces more duration and position two cuts the shot duration down some.

Also, are you using the brown cam with a 30cc accelerator pump? If I remember correctly, the brown and yellow cams are only for use with the 50cc pump and lever assembly - using the brown cam with the 30cc pump will overextend the arm and cause the diaphragm to prematurely fail.

Also keep in mind that when you start using nozzles over 37 you need a high-flow nozzle retaining screw (it's hollow so it reduces restriction in the pump circuit and the nozzle puts out its full rating).

Good luck and have fun!

 

When I did my research prior to tuning my carb, the information directly from Holley said to use the high flow nozzle starting with the 40 squirter.

 

Well I tried a set of .040 squirter jets, and to be honest I didn't notice too much of a change.

Question. You know how if you retard your timing, the engine will be flat on it's face until the mech. advance advances enough? Does the same apply if the mech. advance doesn't advance to total advance quick enough? I know the goal is somewhere between 2500-3000, but what if it was 4000+? It seams as if when it's under load and I'm cruising and start to press down on the gas, it just doesn't want to spin faster. I'm starting to think that I don't have my timing "all in" soon enough. Let me know what you think!

 

Well I think I found the issue that's causing my problem which led me to think that the carb wasn't adjusted right. My mechanical advance isn't starting to advance till around 2500rpm's, so the timing retards to about 7-8degrees (10initial) untill that rpm, so I have almost no power. I'm goin to mess with the springs today and see if I can make it better. I guess the heavier spring is supposed to have some lash in it which it doesn't right now.

 

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