Can somebody help me understand, in know what jets are and I know what squirters are and what they both do. But I don't understand how going up in jet size will really effect the amount of fuel that comes out of the squirters. A squirter has specific size opening and no matter how much fuel you supply the squirter, the opening doesn't get bigger for more fuel. Kinda like a garden hose, you will never get more water out of a garden hose if the opening the water comes out if it set at a specific size, right or wrong? I am trying to cure a slight off idle stumble and don't see how larger jets would help?

Two different circuits entirely --- jets are main metering circuit and squirters are transition circuit.

Jets are down in the float bowl and screw into the metering block. they control how much fuel is pulled through the venturi (the round thingy's in the center of each barrell). The larger the number the more fuel it will flow, the smaller the number the less fuel it will flow. More fuel = richer, less fuel = leaner.

Squirters are located between the front two barrels held in place with a phillips head screw (there is one on the secondary of a "double pumper" carbtoo). The squirter(s) are part of the accelerator pump system. The smaller the number (stamped on the squirter itself) the smaller the hole and the LONGER it takes for fuel to go through it. the accelerator pump cam is what really controls how MUCH fuel gets pumped. By changing the combination of pump cam and squirter size you can control how much fuel is pumped and how long it takes to pump that fuel into the carb. the goal is to pump enough fuel over a long enough period of time to "cover" while the carb transitions from the idle circuit to the main metering circuit.

If you are trying to fix an off idle stumble you are dealing with a transition circuit calibration issue. Double check your float levels first (fuel should come up to the bottom of the site plug on the side of float bowl). Then go back to the factory cam and squirter if you have already changed them. It doesn't hurt to make sure you have the right power valve either - pick one that is rated 2-3" below your lowest steady vacuum reading when idling in gear.

If you nail the gas from idle and the engine pops you have a lean stumble (most common). If the engine just gets real lazy for a second and there is a puff of black smoke out the tail pipes you are too rich (less common).

To fix a lean stumble The first thing I like to do is to go down a size on the primary squirter. this makes the pump shot last longer, which is often the problem rather than not enough fuel. If the problem gets worse go back to the other squirter and go larger on the pump cam. Just make only one change at a time or it gets confusing.

A rich stumble almost always requires both a smaller pump cam AND a smaller squirter.

Good luck.

So the fuel that gets dumped into the manifold comes from two places, the squirters and the venturies? I was under the imression that all the fuel I use that goes into the manifold is from the squirters, this being the only place fuel is dumped into the manifold. Basically I put a 1/2 inch carb spacer and now have a slight off idle stumble. I would assume this is alean condition do to more atomization of the fuel. i get no poping or anything just a slight stumble.

Originally posted by Erik Beckett:
So the fuel that gets dumped into the manifold comes from two places, the squirters and the venturies?

Actually there are 3 completely separate places fuel goes into the engine - the acelerator pump (squirter) the main jets/venturi, and the idle transfer slot. When idling fuel comes out a tiny slot down by the throttle blades - the mixture screws control how much. Raw fuel should never actually go into the intake, idealy it is thoroughly mixed with air before it gets into the manifold.

I was under the imression that all the fuel I use that goes into the manifold is from the squirters, this being the only place fuel is dumped into the manifold.

NO - fuel only goes through the squirters only when you push down on the gas pedal. If you never move your foot, gas never comes out of the squirters. the accelerator pump only shoots out gas when your foot mashes the gas.

Basically I put a 1/2 inch carb spacer and now have a slight off idle stumble. I would assume this is alean condition do to more atomization of the fuel. i get no poping or anything just a slight stumble. Try a smaller squirter. stock is usually a #31 try a #28 or even a #25. You might have to decrease the back squirter size too. Make sure that the lever that rides on the pump cam isn't loose - there is an adjustment nut that will take any slack out. Don't adjust it too tight either, you should be able to move the acelerator pump lever an aditional .050" after the throttle is fully open. Check the linkage adjustment whenever you change pump cams.

A 750 DP is a pretty big carb for your combo. It may be a little tricky getting it tuned for your engine. Smaller squirters should help. You might also have to run smaller jets, if your plugs are black or very dark brown go down two jet size numbers at a time alternating front to back until you get a light tan colored plug.

Start by decreasing the front - if you have a #74 go to a #72, if it is still rich go smaller in the back - like from #84 to #82. Then go back and decrease the front again if it is still too rich (like from #72 to #70).

I once ran a 700 DP on a 355 combo very similar to yours and I would up going four numbers leaner in front and two numbers leaner in back AND a smaller pump squirter in front.

Just to give you an update. I was tweeking the carb this weekend and I noticed some leaking burnt gas on the back of the manifold. So I tightened up the back bowl and two of the bolts were finger loose. Now the top bolt that holds the bowl on never tightened up, it freakin striped. So now I am wondering if this is a vacum leak I had. If fuel comes out the air can go in right. Last year I had to fix an off idle stumble with larger squirters and all I did was put a 1/2" spacer and the stumble was back. It very well could be related to the bolts being loose. It had 35 squirters in the front and 31 in the back. Should these be the same. Now the big problem, do I JB Weld the bolt and rethread or use a heli coil if I can find one the right size?

Hi, Eric. I too have a 355 with a 700DP, performer rpm,etc. I'm hazy on other specs as the motor came with the car. However, it has a crane solid ft and yields 240 psi on a compression test. I'm running stock jetting and have made the other adjustments. Do these carbs tend to come too rich out of the box. I know it's not good to make generalizations but you caught my attention! Thanks.

All I can say is I had to jet mine up and use larger squirters last fall. Know that I put a carb spacer on I don't see how I should have to go to smaller squirters. The plugs look good, maybe a tad on the rich side but not enough to change jets.

Rick, IMO the Holley 4150 double pumpers tend to come a little on the rich side.

The stripped thread thing is hard to fix. If its just the bolt get a new one. If its the threaded hole in the carb main body maybe a 1/4-20 Helicoil would work. Maybe a new ProForm main body would kill two birds with one stone.

BTW you don't need a lot of TQ just enough to seat the gasket. I like using a nut driver to tighten them up. Could be a good excuse for a new carb.

Good luck.