Reply to "Tuning help needed"

Thanks lastpushbutton for the kind words.

PVs usually come in x.5, standard in most carbs is 6.5 and it tells at what vacuum the PV closes. An engine with a wild cam would have a lower vacuum, so maybe a 4.5 PV. They're usually stamped e.g. 6 and 5, meaning 6.5. I sounds like your kit has a 3.5 and 7.5 where the 5 is so weak you can't see it?

However, if the engine now works fine except an immediate hesitation, I would guess an accelerator pump issue. Most obvious, is it adjusted so that as you move the throttle there's instantly a spray of fuel? There should be. If yes, then maybe the amount of fuel is too small, need a bigger shooter? But first, adjust end play as described below, that's free.

Paste from www.tuningmadeeasy.com:
Tuning the accelerator pump
Again here we would say the set up when buying would in 80% be perfect. But if you bought too big a carburetor as many people do, then there’s a bigger “hole” to cover when you smash the pedal to the floor, so more pump shot is needed. There are many things you can change on the accelerator pump. The total volume, standard is 30cc, a bigger pump can be bought pumping 50cc. We’ve so far never seen an engine needing more than the 30cc though. Secondly the speed of the “arm” can be adjusted by changing or moving the colored plastic cam on the throttle shaft. It determines the volume in relation to throttle position. A Holley kit contains the following cams (least pump shot->white, blue, red, orange, black, green, pink, brown->most pump shot). Thirdly the size of the holes in the shooter determines how fast the fuel is squirted into the bores. So adjustments are infinite. Which makes things easier but also more complex. This is not just a screw you can turn.
One thing before we start. Regardless of which colored plastic cam and size of pump (30/50cc) it’s critical to adjust end play when throttle is fully depressed. If end play is too much you lose pump action, if it’s to little you end up destroying the pump. End play is determined by opening the throttle fully (engine off) and then seeing how much further you can press the accelerator pump at the are situated on the fuel bowl. You should be able to create a gap of 0.4mm, adjust spring just above to obtain that.
You need to tune the accelerator pump based on two sets of info. Is it too little or too much? Is it too soon or too late? This must be based on experience when flooring the pedal. First though, let’s get rid of a myth. People that experience a stumble when suddenly accelerating often describes it as “it wont take the gas”. It is in fact the opposite that happens, the engine doesn’t get enough gas to cover the “hole” when the pedal is pushed down, throttles open and vacuum drops. So what’s your experience? Does it stumble or is there smoke out the exhaust? And is that condition immediate or after few seconds?

Immediate stumble:
Here the accelerator comes in with too little to late. This can be solved by either changing the cam to one that provides more shot earlier, or a shooter with bigger holes. Notice the spring on the accelerator pump arm? Fluid can’t be depressed, so when the pedal is floored, the spring depresses and only extends as fast as the holes in the shooter allow. So if you need to get more shot faster, it’s the cam or the shooter size. The cam comes in kits, normally with data on each cam. If not, put them on top of each other, you can clearly see which has the most aggressive profile. Shooters are starting around size 0.025”. Go up approx 0.003” at a time until the problem is cured. What’s best, cam or shooter. Well a cam kit is a lot cheaper than various shooters, and in 90% on the cases it solves the problem.