nutherjrfan UberDork
10/17/20 6:18 p.m.

'04 Yamaha Vino YJ50 49 cc 2 stroke.

Impound purchase being passed on from the neighbor.

Added a missing choke piece ( OE ) to the carb and cleaned it.

Put a standard OE exhaust with new washer on.

Also Yamaha air filter that I put a lot of Yamaha oil on. Oops? Sticky stuff.

I've since washed it a little with Yamaha air filter cleaner.

Threw some gas he had in a yard can into it.

Currently using a Zuma cap. ( Ran it with it off no difference.)

New correct  Yamaha approved spark plug.



Will rev freely on the kick stand.

Add 175lbs of human it goes but shortly doesn't. Will idle.

If you half to fully open the throttle it dies. The slightest incline bogs it down.

But put it on the kickstand it'll wake the dead.

What gives?

The neighbor should be home later.

p.s. neighbor is often wrong/ never in doubt on car/ bike stuff but knows far more than I do at this point.

Mr_Asa SuperDork
10/17/20 6:27 p.m.

Not getting enough fuel.  Possibly even not filling the carb bowl?  The incline symptoms make me think of that.

The yard can gas also concerns me, considering it is a 2 stroke

nutherjrfan UberDork
10/17/20 6:36 p.m.


I just realized I should clarify.

The neighbor did the carb stuff, his gas etc.

For the heck of it whilst cleaning the air filter a little I tried to start it with the air box cover ajar. No go/fire.

I'm learning now that it's in my

Donebrokeit UltraDork
10/17/20 7:10 p.m.

Dose this engine use reed valves? My brother played hell with those back in the day.

nutherjrfan UberDork
10/17/20 7:16 p.m.

In reply to Donebrokeit :

Apparently two strokes don't have valves.

This is all new to me.

I just got off the phone with the neighbor.

Months ago I asked him should I buy a V belt. He said no then.  Maybe now.

Grrr. Back out on the bicycle tomorrow to afford that. Less than $50 even with Partzilla. I actually looked it up again before calling him as my thoughts went that way.

Jesse Ransom (FFS)
Jesse Ransom (FFS) UltimaDork
10/17/20 7:26 p.m.

You were talking about the carb, so I assumed " Add 175lbs of human it goes but shortly doesn't" meant "engine stumbles/won't pull" but now you're talking about V-belts, so I'm a little confused there... Is it revving and not going anywhere, or is it failing to rev under load?

Reed valves are a 2-stroke thing, but not all 2-strokes have them. They don't do the same job exactly as 4-stroke valves; they act as a check valve so the air/fuel charge doesn't back out into the carb so much on reversion (more or less/my-understanding-such-as-it-is).

I think Mr_Asa's question about float bowl height is good, and the other thing I'd wonder about is whether some passages in the carb are still blocked. It's a different circuit feeding the carb at 1/2-to-full throttle than what's doing it at and just off idle. I still think Kevin Cameron gives the best step-by-step explanation of carbs across throttle ranges.

Mr_Asa SuperDork
10/17/20 7:29 p.m.
nutherjrfan UberDork
10/17/20 8:01 p.m.

Good replies.

Under load seems to be the problem.

I did the kickstand test then sat on it for a couple of minutes googling symptoms.

After that it picked up and did a half circuit of the block before getting stroppy again. And it did go around the block the previous night a few times with only one stumble.

Like I said this all new to me.

The V belt thought is just that.

Thanks for the video.

I love learning new stuff.

nutherjrfan UberDork
10/17/20 8:04 p.m.


Failing to rev past quarter throttle under load.

Dies at just past half throttle.

Sorry. I meant to answer that.

Jesse Ransom (FFS)
Jesse Ransom (FFS) UltimaDork
10/17/20 10:18 p.m.

Huh... When it's making its successful half-lap of the block, will it take half-to-full throttle? Or is it still less than half throttle, but then that stops working too?

The stopping working sounds like fuel flow: clogged filters/lines and/or float level too low. EDIT to add explanation: this sounds like there's enough fuel in the bowl to start out, but it's getting used faster than it's getting refilled. So more about flow than float height, but low height reduces the ability to buffer a little.

I'm sticking with my notion that not over half throttle is clogged passages and/or low float level.

But I am also not an expert!

nutherjrfan UberDork
10/18/20 12:06 a.m.

In reply to Jesse Ransom (FFS) :



Makes sense.

I'm going to try to take the lead on trouble shooting tomorrow.

First I'm going to eliminate the over oiled air filter as the neighbor keeps harping on it.

Btw. Yes it will take full throttle but revert to idle/quarter throttle only.

Onward ho.

Jesse Ransom (FFS)
Jesse Ransom (FFS) UltimaDork
10/18/20 1:05 p.m.

In reply to nutherjrfan :

That's awesome, I think! If it were clogged main circuit, it wouldn't work and then taper off.

I think it's down to making sure fuel is flowing freely to the carb, and that the float level is right.

nutherjrfan UberDork
10/18/20 6:38 p.m.

Well this is what's coming out of the fuel tank.


Looks like I need to treat it with evaporust at the least.

Could I get away with draining and treating the tank in situ or is that way too lazy?


Jesse Ransom (FFS)
Jesse Ransom (FFS) UltimaDork
10/18/20 7:32 p.m.

In reply to nutherjrfan :

Better than nothing, but there's a good chance that there's crusty rust you'll want to knock off as well, so giving it a good agitation with a length of sharp-edged chain in along with the de-rust solution would be good (unless you can see in and it looks tidy). And that involves pulling it...

nutherjrfan UberDork
10/20/20 8:07 p.m.

This is the fuel filter.

I'll most likely buy a replacement.

The tank was shee-it full of rust.

Used bolts and lots of soapy water.

Now sitting with evaporust.

The fuel float is not working. Might as well buy that too. Of course the gas cap is missing.

The petcock downstream of the tank was allowing fuel to drain. Fortunately available and not expensive.

And finally I learned to check the intake manifold when googling the reed valves.

Not sure if that's part of my issue but it'll need to be replaced also.

Oh well it's a fun little project but it is meant to make me money delivering food.


GCrites80s HalfDork
10/22/20 11:32 a.m.

That intake boot going to let too much unmetered air in; it must be fixed.

nutherjrfan UberDork
10/31/20 11:41 a.m.

Parts Cannon is loaded.

nutherjrfan UberDork
11/14/20 3:22 p.m.

New v belt on will run properly if I don't sit on it and jog alongside uphill.

Or downhill sitting on it it'll go fine.

The service manual says belt or variator cam and sliders.

Will order  cam and sliders next. Approx $30 shipped.

Gettin' there. I hope.

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