I need to severelly restrict the power output on a CRF150RB that I got for my 13 yr old daughter. It is way too fast for her to learn to ride on, but I got the bike cheap and one day hopefully she will be able to make full use of the bikes performance.

So far I have restricted the throttle travel to around 15% of full. I have placed an intake (before carb) restricter plate narrowing the intake to only 5/8" and also added a 5/8" exhaust restricter plate between the head and exhaust manifold/pipe. Bike runs good, and although as expected it wont rev out, it still has the tendancy to rip her arms from her sockets and give her a hell of a fright.

Maybe I should be looking at jetting??? Anything to increase the throttle travel for less fuel / air delivery???

Any help would be much appreciated.

Bike details:
2008 CRF150RB

You need to change the throttle tube! You have a race profile cam on that throttle tube, and you need a beginner profile, like what is on a CRF80. You can put a stock honda tube on there from an 80 or and older XR, but you can also put on a G2 brand adjustable tube, so it can be switched back someday for her or the next buyer.

Making the bike run worse will just make it more dangerous, unless you change the jetting (leaner) to match.

I would restrict the exhaust and restrict the air box, but not the carb, as that will cause strange eddy currents that may have bad effects .
You can restrict the airbox by adding restrictive baffles, or putting a plastic bag over the air filter, and then add some holes to limit air intake.

Simple. Come up with something that goes on top of the slide of the carb to limit its upward travel. I once used 1/2" PVC pipe and trimmed it shorter as skill level increased. At some point it can be totaly removed when the rider is ready.

easy just put a much smaller sprocket on it (rear) 4 or 5 teeth smaller that will slow it down heaps the quick jolt, acceleration, will be gone... yeh she will have more top end but how big is the track you ride.

When my 3 children were starting out on Suzuki JR50s the bikes had a restrictor between the carb and engine plus one between the cylinder and header. As skills progressed the restriction holes were enlarged, and finally removed.

The small throttle tube referred to above was used on all XR200R and is a CR Pro model also sold by Motion Pro.

An additional way to slow down bottom end response is to retard the timing. On Trials bikes the mod is to elongate the crank position sensor mounting holes to advance the timing, the opposite could be done to your 150. But my memory says the 150 sensor is mounted in a hole in the left cover, off set the hole and epoxy the sensor back in. I've change initial timing on XR200s to reduce bottom end throttle response and 5 degrees will make a big difference, much more than that and the engine will get very sluggish.

Good luck

You could make the throttle stop in the throttle housing. If you take the throttle assembly apart you will notice there is a specific channel for the eccentric to ride in with a stop at the end. The end is not intended to be a stop but with the correct sized piece of plastic or... say key stock bent and glued in place it would work perfect and be easier to change than getting into the carb. I think a throttle stop is the best way to go.