how should you go about tuning with pump cams? - Hot Rod Forum : Hotrodders Bulletin Board
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Old 10-15-2008, 10:24 PM
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how should you go about tuning with pump cams?

i get stumbling and backfiring with my carb and am up to a #40 squirter and its still not acellerating clean and crisp. I have the stock pink cam and got the cam pack that has all the plastic cams and was wondering what the proper way to start out accelerator circuit tuning is? should I mess around with cams first and then squirter size...or the other way around? I know the pump cams all discharge different amounts of fuel, but some discharge less but have a more aggressive curve...How could something with a more aggressive curve get rid of a bog when it squirts in less fuel? I was going to try the blue or green pump cams tommorow and see if there is any change.

carb is a 3310 750cfm
20* initial timing 36* total
floats set properly
transition slot set properly on the butterflies
silver secondary spring
7.5 lbs fuel pressure
350 motor
6.5 power valve (10" of vacuum at idle and its a 4 speed)
idle mixture scres 1.5 turns out

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Old 10-16-2008, 11:03 PM
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I have found the white cam works best here in Southern California.

It has a quick ramp just off of idle using the #1 mounting hole. (Best used with a dual plane manifold)

The pink cam mounted in the second hole works best with a single plane manifold here.

I suggest not only trying different color cams, but also trying different mounting holes to give you a bigger shot of fuel faster.

Also make sure you adjust the pump lever to a .010 feelers gauge. Try this adjustment before changing cams, it could make a huge difference in performance if it is too tight.
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Old 10-16-2008, 11:38 PM
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I've always had better luck with the brown cam using the stock squirter, I even think I have three pump kits in the basement all missing the brown cam because it was the one that always ran the best for me. Can't remember which hole I always used but it will be obvious which hole is best when you test it.

Next choice would be the stock white cam, they work better on near stock setups.

Clearance is very important, don't make it too tight 0.010-0.015" is just right.

As always what works for your setup is dependant on so many factors that its impossible to make an exact recommendation. I would recommend you get the pump cam right before you start with squirters, squirters are so easy to get wrong and are the last tuning tool you should change and then only to fix a specific problem/issue.
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Old 10-17-2008, 04:32 AM
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Its really hard to say which cam works for any specific engine size
the rule of thumb is this
if initial take off is good then it drops off increase shooter size
if initial take off bogs then increase pump cam.
In your case i would reinstall original squirter and try flipping the pink cam (upside down)
adjust for .015 at wide open throttle between spring and pump arm.
youll be suprized that most people complain about pump shot dont have it adjusted correctly.
flipped pink cam
gives huge pumpshot initially then tapers off.
worked on my 406
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