Dirt Bike FAQ

The maintenance schedule will not be anywhere near as intense for a 2-stroke when compared to a 4. The top end will probably be the biggest hit on your wallet. Expect to do this every year or two (a lot more if you get into racing with it). People on here will say stuff to the effect like, you have to waste time measuring the oil to mix in with the gas. If you think about it, as much as you're changing the oil on your racing 4 stroke like maintenance requires, you'll be dumping every 2-3 rides almost the equivalent of what I'm mixing in. Use a good synthetic oil for whatever bike you choose (my personal favorite is klotz, but there's a lot of good stuff out there). Of the 3 bikes you listed the YZ is the best bet. Honda's CR250 is no longer in production and had weird jetting issues. The KTM SX is super light but does not have the power spread of the Yamaha or it's spot-on suspension. Is the new bike going to be used for trail or MX track? The KTM 250 XC would be a better bet if you plan on riding woods.

That's because the price would vary very much depending on condition and possible origin of the bike and documentation.

for example if it is in running condition and complete. and you are near a track that has vintage racing or contact a vintage racing club. you may have a small fortune there..

A Suzuki 110 is a play bike. It is not sweet for jumping. Is your friend Napoleon Dynamite? Either way, never take his advice on motorcycles again.

Contact your local governing body of motorcycle sport in whatever country you are in for the correct information. In America that would be the AMA and in Australia MA.

Folks – the reason the asker is looking to do this mod is because AMA now has a class for the 105cc modded 80's and 85's.

To be competitive in this class, and since no manufacturer is currently offering a 105cc model, this is the only option.

Standard cylinder on this enigne in nikasil. No sleeve.

To do a big bore kit you will either need to have a liner installed in the cylinder (not the most reliable option usually), or purchase a complete kit which includes a bored and re-nikasiled (or other plating) cylinder.

Because of the change in cylinder volume, standard porting will NOT work. The porting needs to be matched to the new engine displacement.

You can purchase a complete setup like this from shops like Lukes http://www.lukesracing.com/luksr/cr85bigbore105p04.htm

Another option which will actually give much better overall power is an increase and bore and stroke to the new 105cc AMA limit. It's more expensive, but will give at least 20% more torque and midrange power than just a bigger piston.

Companies like Max Power offer these kits http://www.maxpower-engines.com/big-bore-kits/cr105.htm

He'll have to also remember that putting this much more power thru the engine can result in decreased lifespan of transmission and clutch components. Just something to keep in mind!

Pressure from world bodies over noise pollution has stopped production on a couple of the well known brands of 125cc including Kawasaki and Honda. Popularity to race the 125cc has also been down as they quite often have to race against the 4 stroke 250cc and they usually get beaten (of course there is exception to that depending upon the rider onboard).
Part of the reason that honda developed the 150cc was to replace the 2 stroke 85cc although I don't know if it has been as successful as they would have hoped as the idea was for them to race against the 85cc and in America they don't allow that as they race in their own class. Australia has them racing against the 85cc.

Http://www.helmetcamera.com/

I'd probaly go for the We the people bikes because they are super light and are very strong.

If you are only interested in trail riding then have a look at these. klx125, ttr125 and crf150f. All good for trail and would suit someone your height and weight.

Don't get a yz125 if you are a beginner; I made that mistake and regretted it. Simply put it would beat the hell out of a noob trying to ride it in trails.
The reason behind it is that it is a 2 stroke and therefore has the power of about double that klx and twice the kick. The KLX is a non performance (non racing) trails bike designed more toward beginners.

I would highly suggest you stop off at a dealer to test drive both and compare them, you will see what I mean.
I had both a yz125 and a similar one (CRF150F) in the same situation. Dont make the same mistke I did.