Accelerator pump cam selection question
 

Ok, here is my dillema, I had a bog during WOT acceleration on my Holley 750 double pumper and went up from .28 shooter nozzles to .31's with some improvement. Then I replaced the rear accelerator pump cam from a white to an orange one with no improvement. So I go to a brown in the rear and replaced the green in the front accelerator pump to the orange, and bingo the car accelerates without the stumble however now when I come to a stop and let it idle for a few seconds the car tends to load up and will break up until I go WOT and clean her out. I tried going back to the green in the front and still same results.

Now why would changing the accelerator pumps cause me to load up at idle, it never did that before and these are the only thing I changed. Any advice on what to do or what cams to try out? Or should I now jet down the front jets???

accelerator
 

Maybe the carb guys are all on the CARB Forum below this one?

Sound like it's not burning or vaporizing the fuel well, you you give it more squirter to supply more light end fuel that will vaporize to get it rich enough, only to find all those heavier compounds loading the plugs up. Gasoline is made up of a variety of components, most usually it starts vaporizing the light ends around 100˚, complete evaporation and the percentages in between depend on the fuel and may run anywhere from around 220˚ to 300˚to completely vaporize. I would guess either insufficient timing, or too cold on the plug, or a bad choice of fuel for the engine. How about some details on the engine and the car, as much as you can, and timing curve as well as the plug type and part #. Here is a couple spec sheets showing the vaporization curves of each to show you.

http://i287.photobucket.com/albums/l...co_Maximal.jpg

http://i287.photobucket.com/albums/l...co_Supreme.jpg

To see something with a little more difference, go to this link and put your cursor over each to see the difference between them.

http://www.rockettbrand.com/productspecs/specs.html

accelerator pump
 

it could be that the linkage that pushes the accelerator pump may need to be adjusted. you may have to back off of it as the new cam may have started the lever moving sooned and you are squirting gas at idle. this was the case with my friends brand new holley ot of the box. just a thought art

Julian to answer your question. The different pump cam's changes the squirt duration, One color will make it a quick burst and another will make it a long steady stream. Another thing to look at is are you working on it in a garage or out in the open air? I have to jet my carb out in open air mine will try to loadup in garage because of air flow. I have seen engines that you can just sit the hood on and the engine will change just because of air flow.


Mark

Julian Did you get her straighten out yet :?: