startat2

iTrader: (2)

Im currently doing a v6 to 350 carb swap on a 91 RS. I picked up a used holley 4160 750. I slapped it on, have good fuel pressure to the rails, and have fuel also inside the bowls which are filling like they should. However, when I move the throttle, no fuel enters the intake. I've checked the linkages as best as I could and everything looks in place, however I am pretty new to carbs. I also pulled it apart, cleaned everything, and replaced the gaskets, but my problem still remains. Any help would be appreciated!

Damon

Holley accelerator pump has quite a few things that can go wrong with it.

You might want to consult a parts diagram to orient yourself. But here's the basics....

On the throttle arm there is a plastic cam (usually orange in color on a 750 vac sec model) that pushes up on an arm as you move the throttle. The other side of that arm pushes down as the accelerator pump cam raises the other side. On that other side it presses on another arm that actually presses on the accelerator pump diaphragm located on the underneath/driver's side of the primary float bowl. A spring-loaded bolt (can't find a better way to describe it) is the touch-point between the two arms and also serves as the adjustment point and overload relief on the linkage Where the two arms touch you need to make sure they are in proper contact/adjustment with eachother at idle- no slack between the two. Adjustment is accomplished by turning the hex head of that bolt/overload spring. You want them just holding tension on eachother at curb idle- no slop between the two, but no tighter than that. If that looks good the next things you need to check are inside the carb.

Fuel enters the accelerator pump diaphragm through the floor of the float bowl. There is a check valve there. Either a captive ball bearing (old style) or a rubber umbrella flapper (new style). If it's not present, or just not sealing up for some reason the fuel will just squirt back into the fuel bowl instead of out the squirter above the primary venturis.

The second check valve in the system is directly under the squirter nozzle assembly. If you remove the screw that holds the squirter nozzle and flip the carb upside down this sencond check valve will fall out in your hand. It's either a square-ish dowel with a point on the end (newer style) or a ball bearing with a seprare dowel pin sitting on top of it. They are retained in the carb body when you put the squirter back on and screw it down. Remember there are TWO gaskets that seal up the squirter- one thin paper gasket under it and a slightly thicker tapered gaset between the squirter and the head of the screw that retains it.

All this stuff has to be right for the accelerator pump to work properly.

startat2

iTrader: (2)

Wow thanks for the wealth of info. My tension is good on the arm, however it could be the check valve. I do have the ball style, but dont really know the best way to repair/ replace it if it is due for a change. My second valve was the pointed style and is moving freely with both gaskets in place.

Damon

The check ball in the bottom of the float bowl is non-repairable, unfortunately. You have to replace the entire fuel bowl.

I've found that sometimes they get so gunked up that an overnight bath in carb cleaner followed by blasts from an aerosol carb cleaner in both directions and even compressed air can be needed to get them to open and close as they should. When you can hear it rattling freely as you shake the float bowl, you've probably got it working again.