[EKhatch]

I race flat track and on shorter tracks I usually try to gear the bike to just bang the limiter before entering the corner. I have a different type of question as far as if hitting the rev limiter is hard on the motor. Lets remove the higher rpm's from the equation and for arguments sake say the rev limiter is set to a mild 5,000 rpm's so the act of hitting the rev limiter isn't going to be hard on the motor in terms of high revs. My question is that since I have a carbureted bike and the rev limiter is cutting the ignition is hitting the rev limiter bad in terms of excess fuel being allowed in the motor when the plug isn't firing and washing down the cylinder preventing proper lubrication even though it's only during a very short duration? Is this something that is a valid concern? Does that even make sense?

Thanks

[JimDirt]

Since no one has replied , i would suggest PMing leardriver , since i am sure he messes with rev limiters when he is carb dyno tuning , of anyone here , he would most likely have the best answer as to weather they actually affect jetting/fuel delivery

[Aussiecrf230]

Well, interesting question.
My experience with car engines when ignitions were progressively cut out to act as a rev limiter never had any real fuelling issues.
Normally as soon as the limiter was hit another gear would be grabbed and any excess fuel would be consumed in the next burst of acceleration.

I assume you would not be sitting the bike at the limiter for very long either, less you be left behind. Seems a sensible way to gear the bike for want you are doing.

Ideally fully integrated engine management (Fuel and ignition) took all those problems away and show fuel savings as a bonus.

Assuming bikes progressively remove a spark rather than cutout completely, you will still burn say half of the fuel. Anything not subject to ignition is going to be pumped out the exhaust,might be a bit of popping there.

[EKhatch]

Thanks for the replies. One of the reasons this came to mind is that I am thinking of getting a Vortex ECU, bike is an 06 CRF450R by the way, and having a couple of maps be like 500 rpms below stock limiter and then 1000 rpms below stock for those times I find myself in between sprockets I can gear a little higher and lower the limited. The main purpose for gearing the bike this way is to kill momentum before heading into the corner instead of having the bike still building momentum when you shut off for the corner. This helps slow down for the corner since we only run a rear brake.

[JimDirt]

Have you thought about a heavier flywheel or flywheel weight ??? , it would slow the RPM from quickly building and give a more gradual power delivery , it will not change the total RPM , but it will make the transition smoother from on the gas to off , though it would be slight , it might be the "in between" your looking for to bridge the gap , it will also wind down slower so the transition from acceleration to deceleration would not be as dramatic a change allowing for smoother corner power delivery ...just a thought , but smoother is usually faster , so to me , the smoother the power delivery , the faster you can go and still maintain the transition to corner power , back to straghtaway throttle transition , smooth in , smooth out ....

[EKhatch]

Thanks Jim I do have a heavier flywheel on the bike. I think it's the heaviest one I can get without having to modify anything. I haven't really had a chance to ride the bike with and without it back to back on the same track to tell the difference. I think it helps overall though.

I rode a friends bike with a heavy clutch basket and the bike just wanted to push through the corners and was slow to fall off the rpms. I didn't like that at all.

[JimDirt]

It was just a thought on the weight , but as i mentioned before , PM leardriver , if anyone here would know the effects of hitting or modifying the limiter and its effect on fuel delivery , he would , i would imagine the effects would be minimal on fuel and more of a issue with valve life if anything was noticed as a detriment