Yahama pw50 wont run

bbullsj
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bbullsj
Edited Date/Time 6/10/2021 1:31pm
I recently picked up a Yamaha pw50 2 stroke thinking it would be an easy fix for my kid. Turns out it's not, I didn't realize it was a 2 stroke instead of a 4 stroke. It will kick over fine, barley idle, and then bog out and die when any throttle is applied or it idles more than 10 seconds. The previous owner put a 60cc big bore kit on it because he wanted it to be fast but never got it running again and gave up. It came with the old jug and piston which looked fine, a new carburetor, and he put a whole new wiring harness on it.

I don't want to just start replacing stuff on it thinking he bought the cheapest stuff and dump a ton more money into it. I can resell it like it is and get my money back, but would like to fix it for my kid to ride. 

What should the spark plug gap be and what's the correct spark plug for it? The throttle cable seems to be loose at the throttle handle so possibly an incorrect cable (those look new too.



Where should I start with this thing? I did check compression and from 4 kicks I got 60,100,120,140. I've worked on 4 stroke small engines and car engines so i do have some knowledge, just not any with 2 stroke. 






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Paw Paw 271
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Paw Paw 271 6/2/2021 4:55pm
6/2/2021 4:55pm
There are many reasons for bike not to run and in this case too many things have been altered to know for sure what was done either correctly or incorrectly. Why not just dump it and look for another and better project as this one may turn into a money pit.
You will need a service manual.
You will need a tear down and inspection.
Basics...
Are you getting a bright Blue spark when you kick it over?
Are you getting fuel to the carb?
Where is the air filter?
What fuel mix are you running?
Is the fuel mix fresh?
Have you checked to be sure the bottom is loaded up with old fuel mix in the crank case?

With no knowledge of two strokes, no manual, no spec's and no real knowledge of the history of the bike, you would be better off finding a better project.

Paw Paw
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bbullsj
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bbullsj 6/3/2021 1:54pm
6/3/2021 1:54pm Edited Date/Time 6/3/2021 1:56pm
Paw Paw 271 wrote:
There are many reasons for bike not to run and in this case too many things have been altered to know for sure what was done...
There are many reasons for bike not to run and in this case too many things have been altered to know for sure what was done either correctly or incorrectly. Why not just dump it and look for another and better project as this one may turn into a money pit.
You will need a service manual.
You will need a tear down and inspection.
Basics...
Are you getting a bright Blue spark when you kick it over?
Are you getting fuel to the carb?
Where is the air filter?
What fuel mix are you running?
Is the fuel mix fresh?
Have you checked to be sure the bottom is loaded up with old fuel mix in the crank case?

With no knowledge of two strokes, no manual, no spec's and no real knowledge of the history of the bike, you would be better off finding a better project.

Paw Paw
1. Yes- getting good spark

2. It does start and idle for a little bit so yes - getting fuel to carb (the correct amount/mix.....unsure)

3. I have the air filter and box. On or off it doesn't affect it running poorly right now, so I left it off.

4. It has a regular gas tank and an oil tank for injection. It is not running on a premix. I wouldn't be opposed to getting rid of the oil injection and just running a prefix though as it would be simpler.

5. Yes-the fuel is fresh premium.

6. Should the bottom be loaded up with old premix? I think what you're getting at is was there blow-by and it now trying to hydro lock itself? I have not checked that....how would you do that without cracking the case?
Paw Paw 271
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Paw Paw 271 6/3/2021 3:41pm
6/3/2021 3:41pm Edited Date/Time 6/3/2021 3:42pm
I am not talking about hydro lock , but rather an issue where the fuel is not being burnt and thus collects in the lower case. This can happen when the engine is not run hard enough to keep cleaned out.
Pull the spark plug out and kick it over many times to see if fuel comes out the hole. If you get it to run, then run it hard for a few minutes to get it cleaned out.
Make sure the exhaust is not clogged.

Paw Paw
bbullsj
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bbullsj 6/3/2021 5:15pm
6/3/2021 5:15pm
Took the plug out, cleaned it, rolled it over about 10 good kicks, no excess fuel came out. I took the exhaust off and it seemed to idle better but no throttle response.

The Shop

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FGR01
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FGR01 6/3/2021 6:57pm
6/3/2021 6:57pm
PW50 will run like crap with the airbox off or air filter removed. Way too lean. Will bog like a big dog.

Put the airbox and filter back on. Make sure the filter has a light coat of filter oil. If the bike is still bogging try running it with the choke in the 1/2 position to see if it runs better richened up. That will at least help you diagnose.
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AJ565
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AJ565 6/3/2021 9:17pm
6/3/2021 9:17pm
I’ve seen the muffler on those full of gunk and restrict flow causing a big and stall. Those are able to be taken apart and cleaned then put back together.
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Factor E
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Factor E 6/4/2021 2:15pm
6/4/2021 2:15pm
Make sure in the carb that the nozzle insert is in the carb
the needle runs thru this part
the main jet holds it in

customer brought bike w one missing
bogged everytime you cracked throttle open
bbullsj
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bbullsj 6/5/2021 9:45am
6/5/2021 9:45am
I install the air box and ran it-see link below for video. I took the exhaust off to rule it out. It looks brand new and doesn’t seems to be restricted at all. I have the correct NGK spark plug in it with .026 gap (per the manual)

https://youtube.com/shorts/iUx-7ip5-1k?feature=share
FGR01
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FGR01 6/6/2021 7:50pm
6/6/2021 7:50pm
Is the throttle cable actually moving the carb slide? Sure doesn't sound like it.

Also, might be something with the wiring or start/run switch. It's acting like it's stuck in the Start mode.
bbullsj
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bbullsj 6/7/2021 4:52am
6/7/2021 4:52am
FGR01 wrote:
Is the throttle cable actually moving the carb slide? Sure doesn't sound like it. Also, might be something with the wiring or start/run switch. It's acting...
Is the throttle cable actually moving the carb slide? Sure doesn't sound like it.

Also, might be something with the wiring or start/run switch. It's acting like it's stuck in the Start mode.
The throttle cable is moving in the carb. Since it doesn’t change if the switch is in start or run a bad switch seems very possible. How would I check that? Looks like a new one was put on, so possibly installed wrong or was a cheap part.
FGR01
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FGR01 6/7/2021 7:08am
6/7/2021 7:08am
I don't know the exact wiring off the top of my head. I would need to look at a wiring diagram. But I know back in the day cheaters used to disconnect the switch to gain a few rpm's on top. So, perhaps you can just disconnect the switch to test and see if the bike runs correctly?
bbullsj
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bbullsj 6/7/2021 7:05pm
6/7/2021 7:05pm
FGR01 wrote:
I don't know the exact wiring off the top of my head. I would need to look at a wiring diagram. But I know back in...
I don't know the exact wiring off the top of my head. I would need to look at a wiring diagram. But I know back in the day cheaters used to disconnect the switch to gain a few rpm's on top. So, perhaps you can just disconnect the switch to test and see if the bike runs correctly?
It has a 3 wire connector, and 2 other single wires. I disconnected all 3 and it still idled the same with no throttle response.
Premix4Life 6/8/2021 12:07pm
6/8/2021 12:07pm
Following. Good luck and looking forward to learning of your progress. (new PW50 dad here)
bbullsj
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bbullsj 6/9/2021 4:31pm
6/9/2021 4:31pm
So I ohm checked the switch and it tests ok. Got readings when I should’ve and got OL when there shouldn’t be a connection. I found a 4 place/ 3 wire connector that isn’t plugged into anything. the red and green wires run up to the handle bar switch but I can’t find the yellow wire. Should this be plugged into anything? 


with the switch testing good I wonder if I’m down to what has to be a carb issue. I have a brand new carb, no jetting replaced or messed with and it still has no throttle response. I would think electrical would limit that and not a poorly tuned carb. You should get some change even with a carb issue…. right?

mxpappy711
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mxpappy711 6/10/2021 8:46am
6/10/2021 8:46am
there is a small fuel filter built into the fuel petcock, take it out and see if its clogged
mxpappy711
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mxpappy711 6/10/2021 8:47am
6/10/2021 8:47am
its in the exit tube of petcock. might have to run a screw into it to get it out
bbullsj
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bbullsj 6/10/2021 9:33am
6/10/2021 9:33am
mxpappy711 wrote:
there is a small fuel filter built into the fuel petcock, take it out and see if its clogged
Tried all that. Didn’t change anything. Fuel filter is full of gas. Disconnected it as well and nothing changed.
mxpappy711
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mxpappy711 6/10/2021 11:16am
6/10/2021 11:16am
I had one build up so much carbon at exhaust port it was almost shut. Should be able to see it when pipe is off.

Pit Row

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bbullsj
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bbullsj 6/10/2021 1:29pm
6/10/2021 1:29pm
mxpappy711 wrote:
I had one build up so much carbon at exhaust port it was almost shut. Should be able to see it when pipe is off.
Has a new head with the big bore kit and brand new exhaust.
bbullsj
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bbullsj 6/10/2021 1:31pm
6/10/2021 1:31pm
Where can I buy a jet/needle kit for this thing and possible get a little bigger one because of the big bore kit?

Is there a restrictive plate somewhere? I know 2 stroke usually have a Reed somewhere. Is it possible that that’s bad? Going to replace the crank seal as that’s a potential problem and don’t know if it’s been done. Where’s a good place to buy parts?

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