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Accelerator pump cams and squirters.
My Roush 427 has a ProSystems 850DP and I want to reduce the pump shot from both squirters.
The carb came with 50cc accelerator pumps and .045 squirters with the brown cam. It was getting too much gas from the squirters so I reduced them to .037. Engine runs better and now I want to try an even smaller squirter, say .032-.034 to see if it makes any difference. My question is this. If I swap out the squirters to the smaller size, should I also swap out the cam and accelerator pump to the 30cc size or should I leave the 50cc pump and brown cam as is? My objective is to find the size where the engine starts to hesitate at tip in and then go up in squirter till it doesn't. I know I know, I need to get a life. |
Holley has a great site with videos on all aspects of tuning. Holleytv.com It may help dispel the notion that more gas always solves the problem. The balance between the nozzle, cam profile, squirt ccs, secondary tip in, advance curve , power valve and idle screws is a fine one. Finding someone who knows that is the only cure. Changing these parameters in the wrong order, and as I learned, keeping a log of what you change and how it effects performance is a must. Good luck.
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Always change one thing at a time.
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The 50cc pump is fine I would change the Brown cam for something like a yellow which should give a longer slower gas shot
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According to the holley pump cam chart, doesn't the yellow cam come on stronger and faster than the brown cam?
Wouldn't a green or orange cam give a slower, longer shot? Or am I reading the chart wrong? |
Lot of carbs use the pink cam. You can solder the hole shut on the squirter than redrill to whatever you need if it will hold the solder.
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Jim,
I wouldn't worry about the accelerator pump right now but with the smaller discharge nozzles you can certainly drop to the 30 CC pump at some point no problem. Holley HP 850s come from the factory with .032 pump nozzles so you're right on track. I've always had excellent results with the pink cam. HTH. Frank |
Thanks, guys, I have smaller squirters and an assortment of cams on order.
I'll try a .031 squirter and the pink cam and see how the engine responds. |
Keep in mind smaller squirters, all else equal, put out less fuel but for a longer period of time. The way I understand it, you want as small a squirter as you can use without hesitation when you hit the pedal.
I have a QuickFuel Q-850 on a 482 FE, and I think I have 33 or 35 squirters with pink cams. |
I have .032 squirrels with the brown cam on the #2 screw with a 50cc pump and it still wants more.
This is on a 350 based small block Chevy. |
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