Want a CRF150-X. Any ideas?

LuckyStar64

LuckyStar64

PR Addict
I think we talked about this awhile ago, but I did a search, and couldn't find the thread. This winter I was looking to slightly DE-tune my 150R (not the trail bike I always ride-- that's an F). I wanted to do this b/c I wanted to increase the longevity of the motor, and to make it a little easier to ride by taking some of the bark out of the top end-- and hopefully increase the mid range torque.

I'd kinda like to try it out at the Action Sports GP. I'm only 5'4, so I have issues getting through the tight on something bigger like a 125.

For now-- I'm thinking that somebody makes a milder cam for it, and I was thinking a thicker base gasket maybe? Head port or milling? Would a thicker base gasket affect timing? I know very little about tuning (or DE-tuning in this case) a 4 stroke race engine. I have no idea if anybody has done this before. --L*64
 
A thicker base would give you less compression and not affect the timing enough to matter. Gasket material can be bought in multiple thicknesses. This could be your best easiest fix.
 
DO NOT!!! INCREASE the Base or head gasket! This will reduce compression, and reduce low and mid range. Opposite of what you want.
Sprockets are always an easy adjustment and may just do the trick.

To achieve Exactly what you are looking for, advance the Exhaust valve timing (jump one tooth), This will give you more torque and less top end.
If that still isn't enough (on a small CC displacement I think this will do) Advance both Intake and Exhaust (one tooth). But I think on this small of an engine doing both is a little drastic and you will have the response of a turtles turd.
 
Interesting. Would advancing one w/o the other let the motor run right? I'm interested in adding low/mid torque for sure, or to better explain-- I'd like to be able to "chug" the motor some in a woods type of scenario like what you'd find at a GP race.

What are the differences between the CRF250R, and the X motors? --L*64
 
With the Honda motor, you cannot alter the exhaust timing only. The engine uses a single camshaft to drive both intake and exhaust. Jumping 1 tooth will make it much harder to start, harder to ride and it will be a lot slower. Other than that, no real issues.

A thicker base gasket will reduce power across the board (low, mid and top). One small side benefit is the bike will run slightly cooler.

I a going to open the big can-o-worms here: flywheel weight. No additional power, but it will make the engine rev more slowly and reduce stalling. It might also make the bike "feel" heavier, due to the slower throttle response. Some people like them, some do not. Most XC guys swear by them. I have one on my RM250 and love it. Had one on a YZ426 and liked it on faster outdoor tracks, but less so on technical AX tracks. It was GREAT in tight woods.

Major differences between the 250X and the first generation 250R: Flywheel weight (imagine that), increased flywheel drag from a larger stator and lighting coil, lower compression and a different ignition advance curve. And electric start too. To the best of my knowledge, the cams, valves and carbs are identical. The head is slightly different, mostly to accept Honda's air injection system. The combustion chamber shape is the same, as is the intake and exhaust ports.
 
TCracing said:
DO NOT!!! INCREASE the Base or head gasket! This will reduce compression, and reduce low and mid range. Opposite of what you want.
Sprockets are always an easy adjustment and may just do the trick.

To achieve Exactly what you are looking for, advance the Exhaust valve timing (jump one tooth), This will give you more torque and less top end.
If that still isn't enough (on a small CC displacement I think this will do) Advance both Intake and Exhaust (one tooth). But I think on this small of an engine doing both is a little drastic and you will have the response of a turtles turd.
Click to expand...

Sorry I'm thinking twin cam. So jump the cam 1 tooth forward (advance).

This will give the results you are looking for, Maybe more than you want... So it seems all or nothing. unless you can play with ignition mapping?
 
Flywheel weight is a good idea. Like said before most offroad guys run them. A must for a 2 stroke.

Cam timing? I know on the 450s the gear is bolted on. I have run slotted cam gears and that makes some difference. The 250 gear is part of the cam so you only get a full tooth difference. Not completely sure on the 150 but I think it's part of the cam as well. If you decide to move it a tooth, remove the plug and turn the motor over by hand from the crank nut before kicking. There isn't a whole lot of room in the for valve clearence. No need for a bent valve. The bigger bikes will turn over that way. Just not completely sure on the 150. It's been a while since I had one apart.

Maybe a combo of hints will be best. Lower compression will make it run more mellow everywhere.flywheel weight will mostly calm it down so its not so instantly responsive.

Now for my can of worms.....how about a cam? Most cams are hop up cams for performance enhancement. But if it were ground the opposite direction you could reduce hit and performance. A friend of mine had crower custom cut him a cam. Most likely not cheap but a possible solution to your request. I have no clue what dimensions you would need, but I'm sure they could help you. Plus the cool factor of a one off parts is priceless.

Just my two scents. If you need any help let me know. I have a full service shop.
 
Tony, just get the dang thing out and ride it first! That bike, bone stock will be a total blast in those GP races!
 
Good idea. Lets to riding! Oh yeah....I'm at work, have work to do at home, and two lil ones. Crap! I'm out. Lol.
 
I've been spinning wrenches out of my house for about 15 years. Just recently aquired a building in uniontown about 4 miles from kames. Will be putting a moto shop in there. Handle every aspect of bike maintenance and repair. Mods to motors, and suspension and will offer full machining (off site for now) and fabrication. Basically if it needs done, we will be able to handle it. Feel free to call my cell 330-608-9113 if you need anything. I work a machine shop during the days for now so I will answer if possible.
 
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