Jump to content
Sign in to follow this  

1978 TY175 overhaul

Recommended Posts

Hi, I'm new to trials, but not new to motorcycles. I ride mainly KTMs, however I did overhaul a 1979 CanAm 250 last winter.  image.png.54afc4b022bfdb285c9a228b900d1b20.png 

I use the term "Overhauled" because I have no intentions of a complete restoration at this time. I just want it safely ride-able. 

So I picked up a non-running 1978 TY175: image.png.85ca78aa06bfbe39e8b9a0bb05344ab3.png

It is in fair shape, complete, but with a few problems. 

  • Carb floods out and bike will not start due to flooded condition 
  • No air filter,  ordered on Partzilla
  • Oil pump off, but it does have the split cable, I ordered a single cable
  • matching engine# and I have a 1979 frame as well, no other spares
  • My switches are banged up, button broken. Haven't started, don't know if work
  • The pipe and silencer are very heavy, I suspect carboned up. 
  • Tank is very rusty inside
  • Chain and sprockets are shot
  • No front shock damping at all, spring only
  • Tires are hard and weathercracked but hold air!
  • As I dig I find wrong and stripped fasteners, loose stuff, 

So far I have:

  • cleaned the carb and replace the critical mainjet "O"ring. 240 main and 25? pilot
  • Swabbed the carb inlet needle seat with toothpaste
  • Checked the reeds (good) and crankcase sealing (poor). 
  • Cleaned frame and replaced fuel, fuel lines and filter
  • Checked for spark, strong (compression good too) 
  • Aired tires to 12psi 
  • Pulled exhaust off and heated it up on the BBQ. It smoked for 2 hours. It weighed 3.5 kg before I cooked it



The photos did not capture how much smoke came off this. My neighbours are gonna hate me. 

This is where I sit now. Any suggestions? Any Canadian or US suppliers?

  • Like 2

Share this post

Link to post
Share on other sites

Ahhh, darn So I took the "O" ring off the inter pipe connection before I cooked the oil out of the pipe, but I forgot the rubber bushing from the pipe mount bolt. Dang, one step forward, one step back. Oh well, a new bushing is less than $10. 

And the news gets worse. My transmission has neutrals both top and bottom and only 4 of the 5 gears. Seems like 1st is missing and a neutral over top of 5th. Yuck. Looks like engine needs to out of the frame and have the transmission looked at. DSCF5048.JPG.3bd3d88e4594417f29fda39974242671.JPG

Got the carb cleaned up and new "O"ring in place


The main jet is screwed into the big drain bolt in the bottom of the carb. Inlet needle seat cleaned up with a swab and toothpaste.

No leaks, but not start either. Good spark but no hint of fire. Timing?


Share this post

Link to post
Share on other sites

Nice TY, I have a similar model too.

How are the point's doing in the ignition, still good timing wise?

Look up the oil pump and rubber lines to the carb and that these are filled with oil.

Did you clean up the air filter, might be clogged?


The carb set up: VM 22SS

Main jet 240 is OK

air  jet: 2.5

pilot jet: 25

needle jet: 0-0

jet needle: 4L6

clip position: 4th groove from top

throttle slide cutaway: 3.0

The gear lever might have got a hit from stones, often the case to trials bikes, here I would look up first, there is a small cap

where you can look up the gear mechanism right under the sprocket, might do a try out.

Cool bike, for trials riding get rid of as much as possible stuff to get the bike lighter, in original trim that bike hit nearly 100kg.

  • Helpful 1

Share this post

Link to post
Share on other sites


    Before you get into splitting the motor, check the gear selector parts are not totally worn out. On the TY175 they are under the plate which the shift shaft goes through. Unlike the modern Yamaha 2 strokes the shift mechanism is external of the engine case and is prone to wear.

Share this post

Link to post
Share on other sites

Create an account or sign in to comment

You need to be a member in order to leave a comment

Reply with:

Sign in to follow this  

  • Create New...