1998 Kx250 Mods

[mrconfused]

Hello everyone. I just bought a 98 Kx250 and wow what a rippen bike. I run dirt drags with it 435ft straight line. I finished third out of about 12-14 bikes. Where I lost was to a supposedly stock cr250 and a stock kx250. I have a couple mods to my bike already and want to do more. I have a pro circuit pipe and silencer and a vforce reed set up. Looking for add'l things to pep it up. Any suggestions would be appreciated.

Steve

[98kxbanshee]

Being a 2 stroker a wieghted flywheel will make a huge low end difference and pulling off the line or out of the corners. Also slap a fatty pip on there.
On mine I have the Gnarly line of FMF pipe and a wieghted flywheel which really rips on low and mid The only thing with this combination you loose a horse or two of horses on top end, but the bottom and mid will blow absolutley anything you line up too it. No comparision. Even 450s cant keep up with her bewteen 1-3 gear. Do that to get all your bottom and low end pull, then you can work on the high end.

[YurFatMom]

Keep the pipe you have and dont add flywheel, heavy flywheels arent good for what you are doing. You want mid to top power for drags, not bottom end. The thing that will help you the most will be a port job set up for mid-top and head modification for more compression.

[griffbones]

^+1
Except I wouldn't raise the compression as this will cost you top end power and would require backing off the static timing to keep up the over rev. But for drag racing keep the pipe that you already have for sure, and as mentioned a mid to top end port job will do wonders too.

[YurFatMom]

Originally Posted by griffbones

^+1
Except I wouldn't raise the compression as this will cost you top end power and would require backing off the static timing to keep up the over rev. But for drag racing keep the pipe that you already have for sure, and as mentioned a mid to top end port job will do wonders too.

Oops, I forgot about that!

[mrconfused]

Ok so keep the pipe and silencer and the reeds. I just need to find someone to do some porting for me. Any body know where to get a hole shot kit for my bike? Have not been able to find one for the 98 kx250. I come hard out of the hole but seem to lose it on top end maybe I can drop a tooth or two on the rear and hope it wont hurt out ofthe hole.

[mrconfused]

Can someone tell me where to get replacement reeds for my vforce??? Maybe cut and paste a link here????

[don46]

The 98 motor was beastly, one of the best 250's kawi made. As suggested don't go to a fatty/gnarly pipe, staay with the pro circuit. usually a heavier flywheel is slower to spool up but will over rev OK, You could try a PVL ingnition, it is a lighter flywheel and will come on quick. It sounds like you looking for more over rev, porting is the way to go there. You may want to try a Wiseco flat top piston mod, if you think you have power now, do that and you' ll see power, "HUGE DIFFERENCE"

[Sledder]

Originally Posted by don46

The 98 motor was beastly, one of the best 250's kawi made. As suggested don't go to a fatty/gnarly pipe, staay with the pro circuit. usually a heavier flywheel is slower to spool up but will over rev OK, You could try a PVL ingnition, it is a lighter flywheel and will come on quick. It sounds like you looking for more over rev, porting is the way to go there. You may want to try a Wiseco flat top piston mod, if you think you have power now, do that and you' ll see power, "HUGE DIFFERENCE"

I agree, I would not add flywheel weight,rather I'd remove a bit...like most atv drag racers do . Increasing compression ratio will not hurt top end rpm if the exhaust port is raised and the porting is done correctly for the pipe and compression ratio and FUEL you are using. I have made some big power on high rpm 2 strke engines that run at very high rpms AND have had compression ratios up to 17:1. In a general statement,Griffbones is correct,I'm just stating that for the real race engine specialty shops that get big power out of STOCK bores...that is what they do.If you are like many,and there is no tech...just go to one of the shops that do it the easy way and big bore it.

[griffbones]

Yeah, my whole meaning was not to just bolt on a phat head with a high compression dome and then do nothing else, because it will cost you some over rev performance. But porting and other supporting mods would make this a very viable option. Raising compression will still require backing off the static timing just a tad to get decent over rev performance, just oppiset, advancing the timing will increase bottom end performance. Higher compression is also a must if riding at real high elevations. And big bores with out supporting port work will go very flat in the top end range. Like most things, everything is must to work together in order to run really good!

[mrconfused]

I found a guy that will port the cylinder for about 220.00. So I think I will pull it apart and have it done. What are you opinions on the flat top piston???

[griffbones]

Originally Posted by mrconfused

I found a guy that will port the cylinder for about 220.00. So I think I will pull it apart and have it done. What are you opinions on the flat top piston???

It is all a package deal, everything must work together. Your bike probably has a flat top piston in it now, but I have no idea of where the wrist pin is located at on your stock piston compared to what ever piston you are thinking of installing? There is much more than just a flat top shape to the piston that must be considered. Keep in mind that porting for top end will take away some bottom end unless it is done in conjunction with a big bore. Just like a big bore will take away top end if porting isn't done along with the big bore. Make sure your guy is a known good performance man, I have seen cylinders ruined by guys that thought they knew how to port but really didn't understand port time area!