Hello!

I am 20 years old and am brand new to yamaha enduros. My only true experience with two strokes is with a couple custom puch mopeds I’ve built. I have general mechanics knowledge, and fabrication skills.

I am super interested in vintage 2T street bikes. I found this at1 that was built about a decade ago and had a bunch of custom work done to it including custom rear sets and an aluminum triple tree, and I believe a bit of porting done.

The thing is now a bit of a project, and I could use some guidance. While it runs, I was wondering what general upgrades people make to these to get a bit more performance out of them. I’ve heard of people putting ct1 175 cylinders on them, and apparently webco made aftermarket heads for these. I’ve also read that there were a number of different cylinders originally made for these that varied in the amount of ports in them.

I also have no clue what carb tuning/jetting people recommend for these, and what pipe dimensions people go with.

Any advise, article links, or part recommendations you may have for me is much appreciated. I’m trying to gather as much knowledge as possible in the 2 stroke world, and it seems like these at1s are the perfect place to start.







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Nice find.

Engine is a 7 port 1972-73 with reed valve. (69-71 was 5 port piston port) Check base of cylinder on other side, you might already have a 175 (will be stamped 171cc)

Definitely some custom work already done there... looks like quite a large carb.

Welcome. Good to have another young person in this arena. Looks like someone put a lot of work into that one.

Rad! That’s very helpful. I’ll be sure to look to see if it’s a 175.
The pipe has quite a bit of damage. I was also wondering what people are putting on these.

Most people run a stock pipe or a stock-modified "sleeper pipe". There are also aftermarket pipes from back in the day but 99% are "up pipes" like stock as these were originally trail bikes.

If you want another down pipe you'll have to fix yours or make a new one... not common to see a down pipe for sale. Yamaha has pipe specs you can find in the Tech Library but modern pipe design software would probably get you something better.

Do you have more pics? Other side? Close ups of triple?