I’m upgrading my 71 AT1 AHRMA racer with a CT2 reed cylinder and a DT175 head with the center plug. I’m following the modifications in this article in the vintage articles section of this website and was wondering if anyone else has done the same and what they thought of the results. I’ve also converted the ignition to the CT1 flywheel and points .

yamaha-enduros.com/index.php/articles1/7...-up-article/download

Be interesting to hear how it goes & you're obviously right into modifying. So i gather yours must've been battery ignition electric start originally, where ours were magneto AT1's mostly. Could you mount a modern small rotor cdi mag on under the rules or if not then a small rotor one off an early YZ125.

I think the rules would probably allow it but I’ve found the points ignition works just fine

ive done those mods + a few more, my thread is an ag175 cafe racer

Thanks but I can't seem to find that post. Were you happy with the results of the work you did using that article? Was the bike peaky or did it have decent low range? I'm planning on using mine racing cross country in the AHRMA 200 vintage class. I can't wait to get it together and running again, just waiting on a new piston pin.

I've got a TY175 top end on mine with an ordinary old Ag175 head [CT2 type head--just using what i had] & it's crazy powerful. Runs like a 250 & pulls from absolute zero revs & revs clean to redline. Funny what works when it really shouldn't. Pipe i mostly gutted about 40 years ago when it was dads farmbike as a 125 [AT1 magneto model], pipe was falling to bits inside at the time--now its rusting to bits lol. Just dragged it out of hibernation [leave me alone, i'm sleeping]. Carb was a blocked mess of our B/awful stale fuel, so video [not that good] is of fitting a new chinese carb i bought years ago for nearly nothing with free freight. Had to run a 5x0.8 die over a mikuni main jet [picked 190] as had about a size 90 looking at it. 190 is safe & although you can hear it maxing out rich it cleared a bit more & is safe down the road & doesn't go rich when pulling--in fact its 'so good' i'm sort of waiting for it to explode lol. Hope video works as don't know what i'm doing with youtube, or i'll try again. Had a local guy [in "71-ish] modify his CT1 by some hotup [hopup] instruction that looked like what you found except for CT1 piston port cylinder & he was a clever guy with good gear & it fair flew at the time.

ive got mine ported out to yamaha factory 175 MX specs with a proper expansion chamber and mikuni flatslide 28mm, enlarged boyesen reed valves with lower boyesen ports, high compression recut squish band head, converted to 12v cdi and the thing is a weapon with a short ratio gearbox in it. I started with the CT3 hop up article. I raised my exhaust duration a bit too much you lower comp ratio a bit too much and kill bottom end torque and lose top end but the lost power was retrieved by my expansion chamber and high comp head and the short ratio gearbox means its all very useable.

I dont race and havent raced other vintage bikes so dont know how good it is but I love it for ripping around town

have a look in the manuals section on this site, there is a pdf called yamaha factory racing tips which has porting and pipe specs, my pipe is off a 70s triple I think or something (? kawasaki/suzuki?) i dunno but specs are basically the same as the 125 except slightly shorter stinger as it was choking the top end a bit.

www.yamaha-enduros.com/index.php/forum/c...aha-ag-175?start=100

Blimey s900t8v, be good to see your one running in anger sometime, sounds like a weapon. & same goes for willlgord when you get yours going.

Thanks for the info, I’m porting my cylinder on the conservative side. Besides using the article as a guideline I used a degree wheel and checked the port durations which, according to the two stroke tuners guide, is somewhat conservative. My piston pin should arrive sometime this week and I’ll have it together and running. Can’t wait!

I had a CT2 that I did the "hop-up" modifications to. It ran GREAT. I did not send off the cylinder for modifications, but did it myself. As best I remember, 1) ported the cylinder as shown in the article, 2) Installed a larger carb as I had no way to bore the existing one, 3) installed a Torque Engineering expansion chamber, 4) installed a Wisco head, 5) modified the inlet skirt on the piston. Don't remember the timing changes (if any) or the carb jetting. I ran pre-mix at 16:1. I remember the pre-mix ratio because I put 4 gallons of gas and 1 quart of 2-stroke oil in a five gallon can. It did not foul plugs. The CT2 would run like hell, but the suspension was still crap.