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I finally started to grow and I needed a little taller bike. I am not ready to race dad's 250R yet, so dad found a 150RB for me to move up to. Its an 08 with a new piston. They said the valves were good and still in specs so they didn't replace them while they were in the motor. I got home and rode around for a little bit and noticed several things. We bought it from people we know and trust. They said everything is stock except the bars. It has three hours on it since a new piston, but it doesn't have quite the pull that our R does.

1. Can this be the difference in rotating mass of the RB over the R? (bigger wheels, bigger steal sprockets, heavier bike)

2. Could this be just jetting? They didn't appear to know what I was talking about when we starting asking about mods and I suspect it still is running stock jets.

3. Does the AP mod need to be done to the 08, or was that fixed by then?

4. The choke pulled out made no difference that I could tell. Both of our other bikes idle higher with the choke out. Is this an indicator that something is broke or wrong/dirty with the carb?

5. Is the gear ratio from Honda the same on both bikes the using stock sprocket sizes? The R seems to have more low end usable power, and the RB seems to have more top end power.

We have no real mods on the R, because we have just started racing I really can't use all the power I have yet.

1. I wouldn't think the mass effect would be very noticeable. You may want to play around with the rear sprocket gearing though.
2. I would bet this is a majority of the power loss you are feeling. 48 pilot helped mine a lot.
3. Yes, do the o-ring mod. Leave the rivet stock though, it is short enough. Check that the AP squirt is timed correctly.(not hitting the slide)
4. Check and clean choke.
5. Don't know? I thought the only diff. was wheels, swingarm, and fork height. Final drive may be diff. but I think the gearbox is the same.

You may also check the TPS. Mine was out of spec. from the factory. Adjusting it made a difference.

The bike seems to run out really nice, but no guts down low. I am running stock sprockets on both bikes. It seems like the bike wheel has more top end power. Since both bikes are stock, I suspect it is all about gearing. I have a 14 tooth front sprocket, I can put on and see if that makes a difference.

The RB has a 56tooth rear sprocket vs the R's 50 tooth and 15 tooth front. I think the RB also has a 15 tooth front.

Yeah, they run a 15/56 on the 150RB. After running the bike a little bit. I don't think there is a big disparity between the two.