rpm rule

[bullerman]

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.

The same way on mine. I don't have much travel on the gas pedal but I like it. We have the 5500 rpm rule also. One thing on my motor i am not sure about. I removed the governor arm a d spring. I made a new short linkage to go from the butterfly to the throttle lever. I bought one of the aftermarket throttle linkage that bolts to the recoil. The way everything came out at 5300 on the stand my butterfly isn't open near all the way at wide open throttle. Saturday night I was racing around 4500 rpm. I would like to be a little higher. If I set it to where the butterfly opens all the way I am at a little over 5600 on the stand. I don't feel like I am getting everything out of my motor but I don know exactly what to do. The highest rpm I got on the track was with a 15-68.
Next time we race i may open the butterfly up for the first heat race and see if I can tell any difference in lap times.
Someone so sad you can get inconsistent rpm readings on the stand with the aftermarket linkage. I may try the standard hookup and see if that makes any difference. I like the way the aftermarket linkage works though.

 

[bullerman]

only the speed adj. screw . 5300 on a free rev . 4800 on the track have not touched the Governor linkage

I think I should have left the governor on mine.

 

[racing promotor]

The same way on mine. I don't have much travel on the gas pedal but I like it. We have the 5500 rpm rule also. One thing on my motor i am not sure about. I removed the governor arm a d spring. I made a new short linkage to go from the butterfly to the throttle lever. I bought one of the aftermarket throttle linkage that bolts to the recoil. The way everything came out at 5300 on the stand my butterfly isn't open near all the way at wide open throttle. Saturday night I was racing around 4500 rpm. I would like to be a little higher. If I set it to where the butterfly opens all the way I am at a little over 5600 on the stand. I don't feel like I am getting everything out of my motor but I don know exactly what to do. The highest rpm I got on the track was with a 15-68.
Next time we race i may open the butterfly up for the first heat race and see if I can tell any difference in lap times.
Someone so sad you can get inconsistent rpm readings on the stand with the aftermarket linkage. I may try the standard hookup and see if that makes any difference. I like the way the aftermarket linkage works though.

What size track

 

[bullerman]

About 650' around the line we run.

 

[bullerman]

I did back all the way off on the throttle stop screw with the governor on. Worked the throttle lever with my thumb. I got right around 5600 on the stand with the motor surging. I thought it might effect it on the track so I removed the governor. If I could have the governor at race at 4800 or 4900 that would be good. I raced at 4500 Saturday night and that might be good. I am not sure.

 

[racing promotor]

I did back all the way off on the throttle stop screw with the governor on. Worked the throttle lever with my thumb. I got right around 5600 on the stand with the motor surging. I thought it might effect it on the track so I removed the governor. If I could have the governor at race at 4800 or 4900 that would be good. I raced at 4500 Saturday night and that might be good. I am not sure.

No 4500 is not good target 4800, but your wayyyyyyyyyy off on gearing with a 15/68 for 650 lf track, with a 15 driver you'd be around 54 rear and if it grips up any amount a 54 is to much, I'd put a 16/58 on it and go from there. A track here is 680 lf of track and on a fri night the gearing is a 17/58 but this track grips up real good and makes a lot of momentum.

 

[bullerman]

I will try that. What happens if it run that and I turn let's say 4200 rpm. Seems like I to have to go smaller in the front or larger on the rear to turn more rpm. I had a 16-60 on it first time on the track but was only turning 4100 or so rpm but I had some of my fastest laps. At a 16-68 I was at 4500 rpm on the track. I just don't see how I can be at 5400 on the stand and 4800 to 4900 on the track. I know I am doing something wrong. Like I said the butterfly on the carb is probably 80% open. I have already put the 16 driver back on. Thanks for the help.

 

[racing promotor]

I will try that. What happens if it run that and I turn let's say 4200 rpm. Seems like I to have to go smaller in the front or larger on the rear to turn more rpm. I had a 16-60 on it first time on the track but was only turning 4100 or so rpm but I had some of my fastest laps. At a 16-68 I was at 4500 rpm on the track. I just don't see how I can be at 5400 on the stand and 4800 to 4900 on the track. I know I am doing something wrong. Like I said the butterfly on the carb is probably 80% open. I have already put the 16 driver back on. Thanks for the help.

I will try that. What happens if it run that and I turn let's say 4200 rpm. Seems like I to have to go smaller in the front or larger on the rear to turn more rpm. I had a 16-60 on it first time on the track but was only turning 4100 or so rpm but I had some of my fastest laps. At a 16-68 I was at 4500 rpm on the track. I just don't see how I can be at 5400 on the stand and 4800 to 4900 on the track. I know I am doing something wrong. Like I said the butterfly on the carb is probably 80% open. I have already put the 16 driver back on. Thanks for the help.

Confirm at 4500 rpm your last post shows you were on a 15/68, now this post you show a 16/68 which is it ?
RPM on stand has nothing to do with gearing .

 

[95 shaw]

Lmao

Thinking you can get power potential from engine with the butterfly partially closed.

Change to get maximum butterfly opening.
Hook governor back up. Get near 5500 stand limit by adjusting governor screw.

Load with brakes to 48-5000 rpm while watching butterfly.
I am relatively certain this will have butterfly still wide open.
If not, play with governor spring until you can achieve both objectives.
Now adjust gearing to get the best laptimes.

You are leaving too much on table by partially closing throttle to lower stand limit.

Edit. There are reasons to not fully open throttle blade, relating to flow, usually with a specified restrictor plate. At least from my flathead experience.

 

[bullerman]

No 4500 is not good target 4800, but your wayyyyyyyyyy off on gearing with a 15/68 for 650 lf track, with a 15 driver you'd be around 54 rear and if it grips up any amount a 54 is to much, I'd put a 16/58 on it and go from there. A track here is 680 lf of track and on a fri night the gearing is a 17/58 but this track grips up real good and makes a lot of momentum.

With a 15-68 or a 16-68 was within 200 rpm if each other. Almost the same with either gearing.
I will put the governor back on and adjust for as close as I can to the 5500 on stand. So you think with this it will open the butterfly fully while racing. I will try to check it like you said. I Do feel like you said the butterfly needs to be fully open. Thanks for the information. Will post results.

 

[95 shaw]

With a 15-68 or a 16-68 was within 200 rpm if each other. Almost the same with either gearing.
I will put the governor back on and adjust for as close as I can to the 5500 on stand. So you think with this it will open the butterfly fully while racing. I will try to check it like you said. I Do feel like you said the butterfly needs to be fully open. Thanks for the information. Will post results.

You may have to shorten spring.
You can do this by putting zip tie in section to effectively make spring think it is shorter/ or stiffer. Will need to readjust governor with changes to spring.
Good luck.

 

[bullerman]

Thanks

 

[bullerman]

I will crawl all the way out on the limb and say they won't turn 5300 or more rpm/s within the rims of a absolute box stock configuration

only the speed adj. screw . 5300 on a free rev . 4800 on the track have not touched the Governor linkage

Wonder if you got a good one. I am Putting the governor back on mine. I hope for the same rpm your turning. I guess a lot of it has to do with kart and driver also.

 

[mike97760]

To the original poster- You will find 95% of the time that the guys blistering you are doing it in a number of ways that do not have anything to do with the motor unless theyre cheating. Their karts roll very freely and their chassis setups are on point, not to mention their tires. Theyve learned that you never take your foot off the gas, they trail brake if they need to slow a bit. Foot still to the floor. Deceleration on these things is fatal. Yeah I am sure you can tweak it a bit to make it better. The governor arm has a lot of holes in it where the long spring attaches. When assembled the worker that checks rpms attaches the spring in the hole that gives it 3650 rpms. Move the spring to a further hole to get more rpms with governor. And dont get confused about the rpm rules, the 5500 or whatever rpm limit number is checked on the kart stand not on the track. 4900 is all you care about, and thats while racing. As far as the story about a completely box stock motor that ran 5000 rpm right out of the box goes, somebody in China was drunk when they checked that motor. Imagine the poor soul who could have bought that motor to put on his poor little rototiller. Ive been doing this a little while, running stock appearing stuff and small block opens. There was a big box stock race one day and I bought one just to try it. Its kind of maddening trying to get every one my my ducks in a row to run up front. The big race I went to? It was won by a guy who pitted next to me and yanked his open motor off the kart and borrowed a motor from the race track owners water pump. Had to remove it from the pump himself. I loaned him linkage parts to hook it up. And he kicked our butts. Motor was still muddy from its water pump life.

 

[bullerman]

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.

...

You set it at 4280 on the stand?

 

[Collin]

So where do u set this linkeage at

 

[bullerman]

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!

 

[bullerman]

Had to try one more time. With the governor disconnected and butterfly fully opening on the stand. Let it warm up and did three full throttle rev ups.
1st was 5605
2nd was 5644
3rd was 5607
All I could hear valve float. It appears there is no way to get less than 5500 rpm without using the throttle stop and limiting opening of the butterfly which is what I'd did.
So it looks like I will put the governor back on and work with that until I get the desired rpm and hopefully have full butterfly opening.
I wish I could get it right the way I have it but don't think that's possible.

 

[bullerman]

We are running on a 1/5 mile track and if your not turning 5400-5500 rpm they will leave you in the dust. From my testing the stock springs float at 5200-5300. So im assuming that most are running cheated springs and governor.
Also I'm curious if there has ever been a class with a rpm rule. This ruling seems to be very hard to manage, as a lot of little thing could affect ur rpm on race night.

We just started the class. I don't know how it's going to work out.

 

[bullerman]

dynoed two box stock predators yesterday our rpm rule is 5000 did one motor and gov surged at 4700 so we backed the screw out second pull was a tad less power draw your own conclusions . also the motors were 1.5 hp difference between the two. never know what your gonna get. some are mean some are duds most are average. be sure to know ALL the rules there are several things that are glazed over. Dagwood allows up to a 42 jet because they run lean at the rpms we turn they also allow pluging the vent tube with a bearing yet the hose has to be attached etc. a up in jet can be worth 3/4 hp fyi

What size jets do most box stock come with? I was thinking I heard around a .030. So for a box stock on the track could use a .042 to help out?