1985 yamaha tri moto 175 2 stroke, it needs help and I do too.

[Hasteranger]

I bought this beauty this morning. The seller started it on ether so I heard it run briefly.

It also has a lean to the frame. It looks tweaked where the fork goes through the frame.

It's really in decent shape for the age.
I got to tearing it apart. The oil tank had been plugged at some point so I pulled it off.

When pulled the carb out I noticed this is what the fuel lines looked like. Yikes.

I've never worked on 2 strokes before and this fuel block that splits the fuel into a line going to the carb and one going after the carb through me for a loop.

So I got the carb loose and the choke was stuck solid and gummed up. I had to use a punch to break loose that weird ball bearing in it and I can't figure out how it's supposed to work. The punch deformed the ball bearing so I may need a new one.

I have never worked on a carb like this and not sure where to start. I see new ones on eBay for like 80 bucks that say they fit and I wonder if that would be better?


It needs a new seat cover too but first thing is first. Anyone got any advice for getting this thing running?

[ruddy]

Where abouts in the carb was the ball bearing I can't remember ever seeing one iin my carb.
My advice is check u have good compression, solid spark, fresh fuel and clean that carb and fuel pump

[Hasteranger]

Well I posted this a week ago. I've since learned quite a bit on my own. The ball bearing seals off the hole where the choke goes in. The home opens to atmosphere aimed towards the boot between the carb and the cylinder.

So I learned the fuel thing is a pulse pump. I also learned this isn't an 85,its an 83. The only year with that pulse pump. I can't figure out exactly what the pulse pump does or why it's necessary. Seems like it uses pulses from the crank case to meter out fuel. Not sure why they didn't leave it gravity fed like 81 and 82?

Anyway the father in law came over and he brought a rubber stopper type compression gauge. It looks like I have nearly 150 psi of compression. A bit low but not enough to keep it from starting. We put some mixed gas in the fuel line and bypassed the pulse pump and could get it to start, run, and Rev, but after a minute or so the motor falls on its face and dies. It's definitely taking fuel through the carb as we put a funnel on the fuel line and could watch it draw fuel through. More throttle, more fuel.
The choke has a seized cable so we disconnected and removed the cable and left the choke threaded in with no cable. I plugged the passage that had been sealed by the little bb/ball bearing with a machine screw I had.

So at least now I know it will start and run.

My carb only has one adjustment screw, not sure what's it's for but we didn't mess with it. The vacuum line from the carb to down on the right side of the crank case, broke off. There is a plastic piece with the crank case vent and that little vaccuum line and the plastic is very brittle. Hopefully it's common to other bikes and I can replace the whole piece.

I pulled the whole carb apart and cleaned it and out it back together earlier this week. Jets and everything were squeaky clean, surprisingly.

[Hasteranger]

Also I managed to lose the ball bearing/bb thing. Forgot to add that.

[Hasteranger]

So this is the plastic thing that bolts to the lower right side of the case where the vents come off. Does anyone know what this is called and where I can find a replacement? It's brittle and the small hose barb broke off.

[Hasteranger]

I messed around and got it running. Frame is bent so it steers weird not that these things steer easy anyway. Faster than I thought it would be but it's been a while since I've been on a 2 stroke.
1983 yamaha tri moto 175 2 stroke first ride.
I did bypass the pulse pump. But it works fine so I'm gonna leave it this way. I need to replace a few fuel and vacuum lines that are in rough shape and I need a new air filter and a new seat cover but it looks like we might be in business. And if I can get my trailer cleaned off I can probably strap it down and use a big bar and my torched to heat the frame a little and bend it back closer to what it should be.
Oh, and the choke still needs fixed. Had to pour a little gas down the spark plug hole to get it started.
1983 yamaha tri moto 175 2 stroke first ride: 1983 yamaha tri moto 175 2 stroke first ride - YouTube

Weeeeeee!

[galevin]

If you don't mind me asking, what did you pay for that? I bought a couple of those in similar condition for appx $300 each.
Gerald

[Hasteranger]

I'd rather not say publicly. Did either of yours have any bend to the frame like this? The frame isn't the strongest design but it's still pretty sturdy. Just didn't know if that was at all common.

[generallee2005]

The little black plastic cover where the hoses attach is just a carb overflow catch. Just run the hoses to dump to the ground, & skip that catcher.

[Hasteranger]

Can I plug the vacuum fittings on the carb and crank case? I found a new one for 40 on eBay, it's obsolete so if I need it I may pick that up. I'm having multiple leaks with fuel lines and etc so gonna replace all the rubber hoses before I take it on a real ride. Needs a new gas cap, squirrels chewed a hole in this one (why did squirrels always chew plastic gas caps?) . Also need to fix the choke with a new cable, hopefully that's all there is. I pulled the cover off the seat and the foam is pretty excellent so a new yamaha cover should sort it. Took it out today mostly on asphalt. Way fast. Not sure what it tops out at but guessing 60 mph ish.