Planet Minis

mavbike

OK, here goes!

Have a child (11) that prefers 4-stroke power to 2-stroke hit.

We race flattrack.

Looking at 85/150 class for next season. Rules as I understand them are:
*Up to 85cc 2-stroke
*Up to 150cc 4-stroke
*No bigger than 17" tires
*Gasoline (No Methenol, Nitro-methane)
*Water cooled CRF150R not yet allowed

Options so far:
*Get an 85, (what everyone else is running)
*Try to build a 4-stroke that will run with the 2-strokes (trying to teach good morals here, a Cheater Motor is not an option).

To build a 4-stroke,
The DRZ/KLX up-right motor bikes will handle 17" wheels, the XR100 will handle 17" wheels.
I have not seen one in years, but the early Honda SL70 (horizontal motor) may handle 17" and I have found an Orion pit-bike that comes with 17" front, 14" rear that may handle 17's
Would need something no heavier than an XR100, Must have 17's front and rear, target around 18-20 horsepower.

XR100 with 4-valve head may be the only 4-stroke option but that is a lot of money.

Cost is a factor!! But I do have machine shop equipment and can do my own work.

So do I?
*Just give in and run what everyone else is running
*Vertical 4-stroke (probably XR100 based)
*More affordable horizontal 4-stroke (don't know for sure if I can find/buy one that will handle 17's front and rear).

So for you guys that have ridden agains the 85's, What would be the best choice

SUZUKIRM12594

Get a moto hp 150 BBK, bigger head or port/polish stock, a stroker crank, carb/pod filter, 4th gear shift drum, etc.....

Or simply get a Honda CRF150F and mod out...Im not sure it will run with the 85s but...

Get used 04 honda crf 150f (04s dont have the heavy electric starts):
port/polish the head, carb/pod filter, pipe etc...

mavbike

I currently have a 2005 CRF150F, BBR motor with port and polish, still need to get bigger carb (poor boys have to build in stages)
*It's to heavy for 11 year old to back into the corners
*It don't run with the 85's

Although I did consider trying the XR's stage 3 cam, or a Web cam, and already having the bike helps with $$$$. It is just too heavy.

TripleKingCrew

my 168SE ran with 85s.

mr.699

150f build it to the max.

SUZUKIRM12594

Unless you got some serious cash to spend, you should seriously just get an 85 instead of tryin to mix and match parts on these 4-stroke trail bikes...

mavbike

This may be the most accurate response I get.

Truthfully though, there is the challenge + trying to give the child what they want.

dirttrackin280h

I race flattrack as well.
I think your best bet will be to purchase an 85. Building an XR100 to a 150 is going to cost you more than an 85, and it will most likely still not out power an 85.
I raced the XR100's back in 2000-2002, and there was no chance seeing a 100 hanging with the 85's. I know there are faster motor kits today than there was back 5+ years ago for the XR100's, but i still dont see it happening.

Your other option would be to purchase a DRZ/KLX125 and put an EO 190 big bore kit in it, BUT as you mentioned, you dont want to cheat and go over the 150cc limit.

A fully built DRZ/KLX 125 will give an 85 a good run for its money. Give " norcalklx " a PM on here, he know's the DRZ/KLX's very well, and also races flattrack as well.

Its going to be a tough call.

Is your son just starting out racing? Or does he already have experience with FT racing?

SUZUKIRM12594

I guarantee you your kid will love the 85 after a few rides of getting use to. Your kid will probably never want to get back on a trail bike again. Its a very convenient optoin too...Besides if you guys ever decide to start riding/racing motocross or if you already do, it will serve as a dual purpose and the bike and is already allbuilt built up and ready to go to begin with so everyone wins .

chasetheface123

ok if u dont have a price range, get a crf 100 and get the takeagawa dohc head, but if you do have a price range like the rest of the world, get a klx 110 and get a 138 4 valve kit or a 150 kit and a v2 or r head. ported polished, should run with 85's on flattrack

HACKMUNCH

klx/drz125 built makes 20hp

SUZUKIRM12594

I'm pretty sure a 138/4valve would fall under the category of not having a budget. Can you even mix and match a 138 with a 4-valve head???

firepower354

@150cc?

YX150+R?

Fastest guys running 17's? Smaller might be better?

mavbike

Daughter, currently in 65 class. Up until crash with injuries, she was consistently in top 3.
I was ready to look at 85 route. After she tried riding maddog bike (modified CRF150F) she not only said she was more confortable, but she was going faster than on the 65. I own both bikes. At that time the 65 was still faster. With a few more mods, they are now even for power, but the 150 is still a bit heavy.
I know it can be done with the XR100 but I also know what it cost. I don't know about the horizontal motors. (Yeah I know, hard to believe but I have seen XR100 at about 145cc with 200+lb rider, faster than 85's at least that day on that track.) There may be someone on here that can give me an education, but I haven't seen the DRZ/KLX 125's push that much power until at least in the 180/190cc range. Or maybe only people spending the money for the bigger motors are also spending the money for better head?
I knew the best way to get some in put would be to post

Have gotten some pretty good responses so far.

Ya'll keep em commin!

Would like more input on horizontal motors too.

mavbike

Not familiar with horizontal motors other than Honda. What is 168SE based on or a copy of.

aedwards07

I would go with an 85 with a power valve(kx or rm) and a flywheel weight to keep the power smooth.