View Full Version : hesitation, carb accelerator pump?????

07-07-2008, 11:52 AM
I have a 93 prostar w/ a 351 Indmar. I was having idling problems so I took ya'lls advice and got a used Holley 4160. WOW. It idles great. I have small kids so I can idle it at about 600 rpm in gear and I love it. But, I am having some hesitation when accelerating. It stalls a little, sounds like it backfires through the carb, and then accelerates normally. Is this an accelerator pump problem? Where is a good place to get one?

07-07-2008, 12:03 PM
Does it happen when you slam the throttle or in tight turns when on the gas? If so, that is generally the accelerator pump as the culprit.

07-07-2008, 01:23 PM
It usually happens when I am acclelerating normally, like you would pulling up a child skiing. I haven't tried slamming the throttle.

07-07-2008, 07:30 PM
That may be an accelerator pump problem. You can visually check the operation of the pump with the motor off. Just remove the spark arrestor and open the choke plate with your finger and have someone push the throttle forward fairly quickly. You should see a good shot of fuel shoot in two streams from the pump. If it's not a strong stream, or it is late in the throttle range then you need to look at your pump. Look at the actuating arm, it has an adjustment nut that allows you to adjust the clearance between the actuating arm and the cam which is on the throttle shaft. It's obvious when you stick you head in there and look. I recommend leaving about a 10 thousands gap between the cam and the lever when the throttle is at idle. If it's too close the engine vibrations will cause it to piddle fuel at idle, if the gap is too wide you may get a sluggish response out of the hole.

That pump only works when you are moving the throttle forward and serves to help get fuel to the motor, particularly during the 'transition' when the fuel supply is moving from the idle circuit to the main jets.

Your problem may also be caused by a low float setting. Have you checked that? Also, have you checked to make sure your secondaries are opening up? All those things can cause sluggish response to the throttle.

Not sure if that helps. Good luck and post back if you figure it out.


east tx skier
07-07-2008, 08:25 PM
That was my 4010's other problem. IIRC, it was the accelerator pump springs. It was fixed with a rebuild, but wasn't nearly as annoying as the hot stalls.

07-07-2008, 09:00 PM
Thanks, I will look the next time I get the boat out which will be a few weeks. I post what I find. Thanks again.

07-10-2008, 12:33 PM
dont forget bad fuel issues, if it just started and you hear problems all the way through the rpm range you may have gotten some bad fuel. THis happened on my last fill up, suspected it was related to the fuel, sure enough, put some lucas treatment in for the water, ran down half the tank, filled with fresh 93 octane and its back to normal.

07-12-2008, 10:55 PM
The accelerator pump may need adjusted to help it tip in quicker. There is a cam that the lever rides on that can be changed or the lever can be adjusted by bending it.