Vintage Dirt Bike Q & A

Greetings,

My '79 CR 125 is running fairly well now, but there's a few things that concern me:

First of all, the cluth doesn't lift properly. I rebuilt the tranny, and when doing so inspected the clutch basket for grooves that would bind the plates. I ended up putting a different one in from the three parts engines I have that's in great shape. I compared the length of the lifter shaft and thickness of the lifter plate to the others and Clymer manual, and they all were the same (needed a caliper to tell a difference, and it was vvvery slight). My bike won't idle while in gear unless I rev it. When not running and in gear, there is a pretty decent amount of clutch drag when I push it. I've adjusted the cable to its stops, and can't seem to remedy it. Anything else that might be causing it?

On the tuning, it runs well but has a fair amount of exhaust smoke. The flange on the cylinder leaks out huge amounts of black exhaust goo. By the end of a 15 minute ride, the downtube and fender are covered in it. I know its leaking past the pipe, as I installed new gaskets and observed it while running and don't see a leak past the gasket, just out of the pipe. Is there any type of RTV or anything that could seal up the gap between the pipe and the exhaust flange? Even with the leak, should it be producing this much messy black exhaust residue? I don't have a lot of experience with two strokes, so don't know how much smoke/exhaust is normal. I've also thought about putting a stiffer spring from the pipe to the flange to hopefully help keep it more rigid and sealed.

Thanks for your help, this forum is great.

-Pat-

I am not familiar with the 1979 CR125R, but I helped someone with a 1979 CR250R who had the same problem. While the clutch assembly and lifter rod were all in good shape, he found the actuating mechanism (on the other side of the motor) that engages with the lifter rod had worn.

When fitting your pipe put a thick ring of Yamabond around the outside of the exhaust flange. The pipe will squish it up towards the cylinder and it looks a bit messy, but it is real effective. Check that your pipe springs are fresh too. The root cause of the "goo" is that the exhaust temp is not hot enough to burn off all of the 2-stroke oil. You might be jetted a bit rich or have a worn needle jet in the carb. What pre-mix ratio are you running? A good synthetic blend mixed at 40:1 should help...

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Michael Stiles
1979 Honda CR250R Elsinore | 2006 Husqvarna SM510R | 2007 Service Honda CR500R-AF