Box Stock

rpm rule

H

highsidehustler

New member
our local tracks have a 5500 rpm rule and some a 5200 rule. engines are supposed to be box stock. but a couple just blister us. any ideas have to cheat the gov or ideas on why their engines seem to have so much more power?
 
Hemi Pred. or Non Hemi Pred.

The Hemi Pred. will be better.

You can adjust the gov. to give more RPM's.

Maybe they are on better tires for what the track calls for.

1st. post, welcome to Bob's, highsidehustler
 
The governors are factory set at 36-3800 RPM, so if they are getting 52-5500 they have adjusted the governor, have you?
 
Also most tracks running the predator has a $120-$150 claim rule. So I think it's maybe just springs? Or they are cheating the governor somehow.
 
jbthrock said:
anyway you could show a pic of the screw?
Click to expand...

There is a little setup that bolts to the top of the head that has a lever on it, if you look near the lever there is a silver Phillips head screw with a spring behind it, this is the screw they are talking about
 
W5R said:
There is a little setup that bolts to the top of the head that has a lever on it, if you look near the lever there is a silver Phillips head screw with a spring behind it, this is the screw they are talking about
Click to expand...

The throttle stop screw? Yup. You'd want to set it so the throttle lever hits it at the point the butterfly is wide open or you could stress / damage the throttle shaft / butterfly assembly, correct?

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number9 said:
The throttle stop screw? Yup. You'd want to set it so the throttle lever hits it at the point the butterfly is wide open or you could stress / damage the throttle shaft / butterfly assembly, correct?

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Click to expand...
I've been playing with these engines this season and i cannot get the governor to adjust much off of the factory setting. They seem to either work or not. i have also been blistered on the track by following the rules. If you disable the governor and add a return spring for idle, the motor will turn 5200-5400rpm with stock valve springs. So the valve spring float seems to be the limiting factor. If run it straight out the box it will turn 3600-3800rpm and you will be very disappointed. My guess is that rules are meant to be broken or it seems that way for now!
 
number9 said:
The throttle stop screw? Yup. You'd want to set it so the throttle lever hits it at the point the butterfly is wide open or you could stress / damage the throttle shaft / butterfly assembly, correct?

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Click to expand...

No not the plastic one on the carb, the steel one that is on the factory governor assembly that most people take off when removing the governor
 
W5R said:
No not the plastic one on the carb, the steel one that is on the factory governor assembly that most people take off when removing the governor
Click to expand...

Right, the plastic one on back of carb is idle screw, the metal screw with spring around it would be throttle stop. If the factory throttle bracket assy is kept, but the throttle stop screw is removed, when you floor the gas pedal the only thing stopping the gas pedal forward movement is the butterfly / throttle rod bottoming out. The throttle stop screw acts like a "strain relief", unless the gas pedal travel is mechanically limited to stop at the exact point the butterfly is at WOT. It may work fine for who knows how long, but that plastic top on the butterfly / rod assy looks awfully cheap and flimsy to me. I'd be worried it'd eventually fail is all.

I noticed when I switched from flathead to predator that my gas pedal travels about half its distance (or less) and the carb butterfly is WOT.
 
So, when I posted above about the throttle stop screw, I didn't realize how guys may be utilizing them in regards to getting more rpm when dealing with having the gov in place. My boys karts needed a little more rpm, so was messing with them today and see now how guys are using it for those reasons.

I re-bent the loop on the gov spring about .200" shorter - to result in it having more tension. Then I took the throttle stop screw out, removed the spring that was on it, and threaded a nut about 1/2 way down it, reinstalled the screw (without the spring) and added a second nut to the screw. You can use the nuts to lock the screw in place where you want it without risk of it coming out, as I'm not sure how well the weak stock spring would keep it in place if you had the screw backed out real far. A stronger spring would work better and look "legal" if you need it to.

I started the kart on the stand and SLOWLY increased throttle until the lever stopped against the screw and recorded the rpm. Did this several times, with the screw at different positions until I got the max rpm I wanted the gov to allow. I set them at 4280.

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