'74 Mx 250

[FenryHonda]

Does anyone here race a Yamaha MX 250?

My bike needs some bottom end badly. I have a magazine that tests this bike and it says that it is a peaky engine, but there has to be a way to build some more bottom. It does run great once on the pipe.

Here's what my setup is, stock exhaust, including aluminum Skyway silencer/arrester, Boyesen reeds, one size smaller pilot jet, and stock main jet, needle in the 2nd position. The plug is nice and brown, and I have no spooge. The rear sprocket is a 51 and the front is a 14, one tooth down from stock.

Any help?

 

[maicomotoman]

What size is your carburetor? I have found that a smaller carb will make better power down low. Shorten the distance between the carb and cylinder as much as you can. Also, I put a PVL ignition on my bikes to broaden the powerband. I think that you can make power anywhere you want to with the right porting and pipe , but I'm not much help there. Hope this helps a little.

 

[Oregon Trail]

I was reading about someone else that had the same bike and he put on one of these U.F.O's. Said it helped out bottom end. http://www.thunderproducts.com/u_f_o.htm

 

[FenryHonda]

The carb is a 34mm, stock. I just ordered a UFO slide insert and a Circle F pipe today. I may lap the head a little to make more compression. At least I have two spare engines. LOL

 

[Oregon Trail]

I run a Circle F pipe on my Husky and like it. I need to cut down the stinger though, but tucks in nicely.

 

[FenryHonda]

Well, I hope the pipe does the trick. I will have to wait til June to find out. I am a merchant seaman and have been called back to work.

In an earlier post I was told to get the carb as close to the cylinder as possible.... well, I have been reading and it sounds just the opposite. Seems that a spacer tends to make more bottom end. Since I have a machine shop at work, I'm gonna make one and try it in June.