Been lurking for a while and trying to get this bike back to running. I picked this bike up last year knowing nothing about them or 2 stokes. It didn’t take me long to figure out something was different with mine. Behold. There is a MX top end on my HT1. I’ve heard rumor that the early bikes all had the same top end but no confirmation.

There is good reason to believe this bike is original within the first 1000 serial numbers. I’d find it hard to believe that even if the top end was trashed the owner would have converted to an MX top end but I could be wrong. It’s been pretty slow progress getting to where I am today.

Today the jug is up at Bill Bune being bored over with the hope that will get the bike running. It’s already bored .50 over and going to 1.00. Pretty bad scaring on the walls but I wasn’t going to scrap the MX jug. I’ll keep updating on my progress but here it is. 1970 with a build date of 2/70.

One of the few times I actually got it to run. Well never mind. Won’t let me upload a video. Haha

As you are aware your bike is an early production ‘70 HT1. As the HT1 MX was not released until the 1971 model year it would be difficult to believe that the early 1970 (first model year) HT1’s shipped from the factory with the MX cylinder which was not released for a full year. That said I would be interested in having the MX cylinder and larger bolt on carb for my ‘70 HT1 if you come across another.

How’s about this being on the bike?

And this.

All I’m saying is that there is a high probability that a previous owner installed the MX parts.

My first racer was an ht1 with a gyt Kit and a rear knobby. No silencer. Mad neighbors! Carbon maker. Loved it, then got a ct2. Really miss that one, and being a fast kid. Both bikes from Dukes in Fairfield

I had a 71 HT1 in high school. After I stripped out the plug thread on the head I went to my local Yamaha dealer for a new head. They sold me a kit that had the MX head, cylinder, piston, ring, carburetor and expansion chamber for about $60 in 1975. The bikes previous owner may have bought one also.