Vintage Dirt Bike Q & A

After letting my bike sit for about 15 years I have been trying to bring it back to life. I tore the bottom end down and replaced all the seals (http://www.elsinores.com) Uses the same as the CR 250. I'm pretty confident that everything went back together without damage. The bike runs well at low and medium RPM but when I opened it up to about 50 mph the other day I noticed via the rearview mirror a nice long cloud of smoke behind me. The excessive smoke goes away a lower RPM. It didnÌt smoke like that 15 years ago. ItÌs also runs a little rough at the top end. I'm still using the oil pump and it's adjusted correctly. I have probably put about 250 miles on the bike since the rebuild and have not fouled any plugs. I have put a vacuum pump on the transmission breather tube and it holds negative pressure. Of course that only checks seals in one direction. Timing was set correctly with a strobe. I read an earlier post suggesting a dirty exhaust could cause it to burn rich at high end. The pipe was purchase from a salvage yard so I don't have any history with it. Any suggests for cleaning the pipe? I found a suggestion on an Australia web site to fill it with solution of Caustic soda and water. Has any one ever done this? Sounds like nasty stuff to work with. I removed the baffle and managed to work a long thin screw driver up the circle of slotted holes in the pipe. Could there be blockage further up? The only other thing I can think of would be the wrong jets. I did a major clean and adjust on the carburetor. Does anyone know the stock jets for the bike. Currently the slow is .60 the main 122. These 2 agree with my Honda parts book. I'm not sure what needle is in there now (forgot to write it down). For some reason the jet needle is not called out in my parts book. Carb# 004A A. Any help on cleaning the pipe and correct jets would be appreciated.

Had the same exhaust problem...check out post dated 8/14/2003 good luck.

Dana-

Thanks for the reply. Makes me feel a little stupid knowing there were other posts on the subject. Guess
I should have read all the way down. I'm scared to try baking all the carbon out. I have feeling it will only get harder to remove. Sound's like you found the ticket. Did the radiator shop have any negative feed back for you when you picked up the pipe? In other words did the oil/carbon contaminate their tank?

I was thinking of modifying a stock 76 CR250M cylinder to accept a Reed valve, ?
Has anyone ever done this fabrication themselves.
I know that Mugen offered a cylinder that was like this but i never see them.. They are quite unique and much different then the stock CR250M cylinder and head..

Any suggestions..

thanks
Todd A