i could find an mx top end but I enjoy messing with stuff and seeing the results firsthand (I’m hoping for good results). I’m going to modify the intake port with the “fingers “ as in the article. In the article it shows the stock port at 85mm and to lower it to 87mm and add the finger radius to 91mm. My stock port is already at 87mm but more oval. I’ve been opening up the intake to fit my new reeds that came from a RD350. it looks like I may have to add a spacer, they look like they’re going to protrude pretty far into the cylinder. If they don’t work I’ll just use the original CT2 reeds.

Here's the Yamaha factory CT2 MX specs...







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I could insert alot about this , But I dont give out specs that I use. But the exaust port shape is not good . Not saying that you wont make gains , just that there is a better way, trapizoid shape . Also the transfer ports should all open at the same time . Factory boost port angle is wrong . And intake floor make as low as practical and rolled into the crank case , rear transfer ports shouild be hooked in the rear. I can go on . Contact me if you like .

Rich

Well, I’ve started few races on the bike and am extremely happy with it’s performance after my modifications. It runs like a bear, you can bring the front wheel up in first, second and third now with a 15 tooth countersprocket. It doesn’t seem at all peaky, it’ll pull from low rpm’s nicely. I’ve had a couple of issues getting the carburetor dialed in but I think it’s good now. Also I’ve had clutch slipping problems even with new friction plates and sandblasted steel plates. I’ve pretty much taken care of that by adding one extra steel plate and .050” spacer washers under the clutch springs (which measure within specs). The one problem that persists is a downshifting issue from 3rd to 2nd, it’s intermittent but seems to happen at the worst times like right at the base of a steep climb. What happens is you’ll downshift and hit a false neutral after which you have to downshift again to 1st then up again to 2nd. I’ve adjusted the shift linkage perfectly so I think it’s in the gearbox itself. While trying to solve the clutch slippage I ran atf instead of oil and thought maybe that had something to do with the shifting problem but switched back to oil for my last two races and it didn’t make a difference. Years ago I split the cases to replace the crank bearings and wonder if I got something wrong?

One thing I have to say, vintage cross country racing is awesome! Riding some of these rougher courses with 7” of travel in front and 4” in back is a challenge....maybe a little frustrating when a newer (late 70’s-early 80’s) post vintage bike flys by as smooth and graceful ask a deer running through the woods.