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88
Joined
3/9/2019
Location
PL
Hi guys,
Im lost on what is going on our PW50 from 1990. It bogs after a straight section or jump and shuts off. It seems it starves from fuel, when I take the air filter off it seems to rev much higher and cleaner, once I put it back on, problems come back. When checking the carb the bowl had quite some fuel in there so that seemed fine as well. I did the following in the last 2 weeks:
- replaced membrane (was not closing well)
- Replaced piston and checked cilinder, all smooth
- Replaced all gaskets
- New spark plug
- Cleaned carb 3x rechecked everything dozen times, slider, pin, jets, float all is working and clean as it should
- Clean air filter
- Air screw and throttle pin on std position (1,5 turns and 2nd clip position)
- Changed air filter plastic and rubber
- Checked fuel lines and tank
- Unplugged the kill switch completely to rule that out as well
I've had a friend also tear it down who has a son that rides a PW, and he couldn't figure it out as well. Maybe smaller main jet he said or something wrong wirh the air filter, it is a aftermarket one from china, but looks identical to the original.
Anyone has the golden answer?
Thanks my son is so frustrated as he can't get in any flow 
Carbon clogging the exhaust pipe/muffler. Grab a torch and burn the carbon out.
Have you drilled out the hole in the exhaust washer?
Thanks guys. But, yes I also cleaned the whole exhaust already last week. And yes exhaust washer is open and changed it for a regular open one.
CK REEDS PETCOCK KNOWN TO GO BAD REV LIMITER TAKEN OUT? BAD STATOR
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Sounds like a tough issue to troubleshoot.
Check the vent hose and fuel cap...
Sometimes the check-valves in the cap will not flow air into the tank, starving the engine.
You can take the cap off and blow into the end of the vent hose... It should flow a decent amount of air pretty easily.
If it doesn't, some caps can be disassembled and fixed (full size YZ125, YZ250, etc), some just need to be replaced.
I haven't seen this on a PW50, but I've seen plenty of other bikes with this issue. It's worth ruling it out since it's easy to check.
Learned the hard way at a regional. There is a small filter inside the GAS PETCOCK!!!!!!!!!!!!!!!! mine was white Used a small wood screw to remove it! Gas flowed!
check the emulsion tube in the carburetor if it get's crap in it the bike will drive you crazy trying to figure out what's going on
yamaha call's it the main nozzle
This thing? There was quite some shit in there. Did you just leave it out completely afterwards? I'll try in the morning if it is fixed. It seems this might be it, pretty clogged. 🤙🏼
Does it make sense though if that was it that when putting on the air box it starves and taking it off makes it rev higher?
Gas cap air flow checked, is working as it should. I also will check the main nozzle (it's under the main jet right), I did already but will double check.
Thanks
That was it! Bike runs good now doesn't shut off anymore, kid is happy.
Only full throttle it doesn't run right, like it can reach the top. When I take off the air filter it revs much higer. Probably should try a smaller main jet?
Drill holes in the air box cover.
Sounds like you figured it out, but I would get a set of reeds for it anyway, fixed a lot of running/starting issues we had with ours, then you can dial in your jetting
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