Best inexpensive ways to 'tame' a MX 2-stroke?

[RoostRider]

It will be a while before FM gets any more business from my end. At least until my freind gets his back from them (2 week turnaronund HA! it's been 7 and it's still not here... although the guy in Florida who has it says he'll express it to us... :rotfl: ). And just try to get ahold of them on the phone... On the net they are fine with you, unless there is a problem they botched, then they try to cover it up and finally delete your thread when it makes them look stupid.

Thats been my experience anyways.

 

[Crash 142]

To make the 250's easier to ride, I would think gearing it up would be the answer. Get a one tooth larger front sprocket, which should be under 25 bucks. I've never done this, but imagine the chain would still fit fine (not have to be lengthened). Yeah, the rider will have a little less power to start with, but the engine will be tame and manageable.

As someone else mentioned, geraing the bike down with a larger REAR sprocket would make the bike a handful and too responsive for someone learning to ride.

 

[lwsmithjr]

I'm not sure you can fit a 15 tooth front on a YZ. Besides, that would amount to 3 1/2 less teeth on the rear -- That is a pretty significant change.

I have a '99 YZ250 and right after I bought it (after riding a borrowed YZ250F for 6 months) I put a 48 tooth rear sprocket and it (stock is 50) and it lessened the hit enough for me to not be afraid of it. I also have a 13 oz. Steahly Flywheel on the bike. I prefer riding with it, but it is not a huge difference. The two less teeth on the sprocket was the most noticeable -- without degrading the power.

BTW: After I had the thing for about 9 months, I got Eric Gorr to do the "Mo Better" porting. It made the bike easier to ride (power is delivered more linearly)and has more power. My experience was much better than RoostRider's -- I had it back in 10 days (door to door).

 

[Chris_S]

I just installed and tested an 11oz. Stealhy FWW in my '05 YZ250 last night - huge improvement! :cool:

I finally feel comfortable enough to race it in hare scrambles.

 

[RoostRider]

Thanks for all the input... after all this, I think I will suggest a heavier flywheel, a smaller CS sprocket (they are cheaper than a bigger rear), proper jetting, and a warning to be careful... lol

 

[Chief]

Cheif, what do you mean by setting the preloead? preload on what?

Knobby,


Setting the tension on the spring that holds the powervalve closed.

The powervalve is a flap that slides up and down to partially cover part of the round exhaust port. It is actuated open mechanically by how fast the crank is spinning. Higher rpm puts more force on the opening action. The PV spring works against the opening force. If you tighten the spring, the PV opens at more rpm's than stock, if you loosen the spring the PV opens at less RPM's than stock.

If you have 3 small covers towards the top of the cylinder (one in front and one on each side) then your bike probably has a PV. I don't know when they started using them.

On my bike the tension adjustment is a round cover maybe slightly larger than a dime. (Right(?) side upper cylinder. It has a straight across line to grip it with pliers and twist it. That is what either tightens or loosens the spring that wraps around a rod that links up to the PV. The adjustment is held in place by 2 small hexheads. The round cover has notches all the way around to accomadate the 2 small hexbolts so it stays in place.

That is the setup on my bike. I have seen some rotax engines that have the adjustment as a plastic hand twisted knob on the front cover for ez access. I've been told some makes have no external adjustment. Guess it depends on the make model year of a bike.

Chief

 

[Crash 142]

Buying a smaller CS sprocket will gear the bike down. making the power more of a handful. Is that what you intend to do?

 

[fuzzy]

Porting would be my choice, but is not reversable. A mild port job geared towards smoothing out power would be a good choice that you might not ever want to reverse. Also as far as jetting, the needs is often overlooked. Different needle profiles can completeley change an engines character. I cam make my 250 go from a severely hard hitting beast, to electric smooth w/ a needle change.

 

[MX-727]

I've had good luck with putting the smallest countershaft sprocket on with the largest rear sprocket. The bike will have more hit, but it will be SLOW. This should help them get used to riding in the higher RPM ranges without feeling like they are going so fast. You may have to get a longer chain with this setup, but since this is temporary, you can get away with the cheapie chain and sprockets.

 

[Kpicha]

I've had good luck with putting the smallest countershaft sprocket on with the largest rear sprocket. The bike will have more hit, but it will be SLOW. This should help them get used to riding in the higher RPM ranges without feeling like they are going so fast. You may have to get a longer chain with this setup, but since this is temporary, you can get away with the cheapie chain and sprockets.

If you don't mind my asking, what kind of mods did you do to your daughter's KX100 to "tame" it down? I just picked up an '03 and am looking for some ideas. Thanks!

 

[MX-727]

I found that she started out riding real slow, never getting on the pipe and shifting way early just to say she made it into 3rd or 4th gear. I changed the gearing, but she would just shift earlier. I ended up making her ride the track in 2nd gear and letting her know that it was OK to rev the bike. The bike does have an abrupt transition when it comes on the pipe, but if they keep the bike on the pipe, it is fairly smooth.

So, to answer your question, I didn't do anything to change the power of the bike. I just made it easier to keep the bike on the pipe without her riding at warp speed. I have since gone back to the stock gearing and she is riding well.