rm 144 porting

I went with the mid/top porting with the higher compression head (race gas only) mod's it still torque's way better then it did stock as a 125. I recommend putting a 14 tooth up front instead of getting to much wheel spin I now got drive/snap. I crack the throttle just barely in first and it's up in a wheelie. If you like to rev out the bike go for the mid/top porting I was worried at first. But now afterwards I don't know what I was so worried about I'd do it again.

I chose the mo betta on Eric's recommendation. I explained to him that my primary goals were ease of ridability and quick corner exits. Mid Top is generally recommended for experts who keep the bike at/near the rev limit. The mo betta gives you a broader power spread - the best way I can describe it is that the spread is similar to stock - but it has about 20% more HP everywhere.

The mo betta revs better than stock anyway - at least on my bike.

I'm not sure why MXP1MP would recommend a 14 tooth front sprocket. Stock is a 12 on the RM. (Perhaps the YZ uses a 13 stock). Moving to a 14 tooth front is about like going from a 49 rear to a 43 - it will give you a LOT less bottom and more top - it would likely be almost unridable.

When my motor was stock, I did experiment with an 11 front to pick up low end. That is totally unnecessary with the 144. I moved back to the 12 and am currently running a 50 rear instead of a 52.

adamant said:

Now that you are used to the power delivery rob are you still happy with the bike over all, or do you now feel that you would maybe up grade to the mid-top if you could, if it was at no extra cost or hassle ? Do you need to slip the clutch as you would with the stock bore machine ? Also what oil mix is recomended for the bike I am thinking now 32:1

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1: I wouldn't change a thing. Member here "bclapham" also had an 02 RM 144 - mo betta - he was about 200 lbs and racing at very hilly Glen Helen - he loved it.

Given the added torque of the 250f, I don't know why anyone would really want to make a small bore 2 stroke more "peaky". I didn't need more top end (although I got it). I wanted the low mid addition because my primary difficulty in racing 250f's was corner exits. I couldn't seem to get enough drive out of the corners to get past a guy of equal or near-equal speed on a 250f. The mo betta helped a LOT - even with my gearing change.

2:You'll always be slipping the clutch on a small bore 2 stroke. It's just part of the deal. However, you won't need to do it quite as much and you'll likely be able to ride a gear lower than you were before.

On the track I race on the most, I am a gear lower virtually everywhere. I used to have to hit 4th to clear that double you saw me dive bombing (BTW, I didn't crash - Whew! - it was my 2nd attempt ever at a "real" double and I didn't hit it fast enough). Now I'm hitting it in 3rd and clearing it easily. I could probably flat land it in 3rd now if I was REALLY on the gas.

My bike had a Hod Rod, Hinson Clutch and Bill's Pipe/Silencer when I got it. Other than that, the 144, porting and head work are all that's not stock.

Eric can give you the low down on all the other stuff. . . He told me the Bill's pipe would be fine.

The YZ has a 13 front stock and going to a 14 up front is like taking away 3 teeth off the rear my bike still torque's better than it did stock by far. It has alot more pull/snap plus I'm now getting more pull out of each gear so I can rev each one out longer.

The other bonus was it got rid of the wheel spining I was experiencing in the lower gears like 1st n 2nd.It's now hooks up n drives forward not wasting power spining up to fast cause of increased power/torque. It makes enough power now it pull's the larger tooth no problem plus I got back some top speed. It was the best mod I did to my 144 over the Vforce V3 or the factory fatty pipe.

MXP1MP said:

The YZ has a 13 front stock and going to a 14 up front is like taking away 3 teeth off the rear my bike still torque's better than it did stock by far. It has alot more pull/snap plus I'm now getting more pull out of each gear so I can rev each one out longer.

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Same story here - except I went from an 11 to a 12 and from a 52 to a 50. Still more pull and as noted, I'm a gear lower everywhere.

that sounds like a good mod i had a ktm 200sx and it had the same trannie as 125sx but the put a bigger sprocket on front and went from 49 i think ti a 47 was suppose to be like 9 teeth less and it was awsome only makes sense that a person would have to do the same thing if you goto 144