problem with pw50

benrussell
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benrussell
Edited Date/Time 7/24/2014 3:32pm
once it gets to almost its top speed, the throttle seems to almost disengage (for lack of a better way to describe it). like it is reving really high and then it starts put put puting and then if i realease and repull the throttle it will go back up and then bog down again. even if i keep the throttle pulled all the way it revs high (like it should) then bogs down and then it engages for a couple seconds (and i can feel it accelerating) then bogs down and up and down and up and down. any clue as to what might be causing this?
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langhammx
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langhammx 7/21/2014 6:35pm
7/21/2014 6:35pm
Sounds like it might have a clogged jet and is leaning out (seizing), once up to speed ?? Just guessing, but I'd replace the main jet or clean it REAL GOOD for starters. If you still have the injector, check to make sure it's working properly, we used to block it off and run pre-mix to insure proper oil/gas mixture. Good luck.

If that doesn't work, it could be a stator heating up, once it gets going ??
mxpappy711
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mxpappy711 7/21/2014 7:41pm
7/21/2014 7:41pm
There is a real small gas filter built into the petcock of a pw. It is in line where the fuel hose hooks up. You will need needle nose pliers to get it out. Clean it , or leave it out and replace it with an aftermarket inline one.
hvaughn88
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hvaughn88 7/21/2014 7:48pm
7/21/2014 7:48pm
mxpappy711 wrote:
There is a real small gas filter built into the petcock of a pw. It is in line where the fuel hose hooks up. You will...
There is a real small gas filter built into the petcock of a pw. It is in line where the fuel hose hooks up. You will need needle nose pliers to get it out. Clean it , or leave it out and replace it with an aftermarket inline one.
I'll be honest, I've torn into my son's pw more times than I care to, and I never even knew that. It may be common knowledge but I sure didn't know and I Appreciate the info.
F150Motocrosser 7/21/2014 7:51pm
7/21/2014 7:51pm
If you don't do it already, using compressed air (along with the usual aerosol carb cleaner, etc) can make a world of difference at getting build up out of even every little crevasse of every circuit in the carb.

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newmann
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newmann 7/21/2014 8:14pm
7/21/2014 8:14pm
Does the PW have a restrictor plate washer in the exhaust manifold?
dirthead1
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dirthead1 7/21/2014 9:18pm
7/21/2014 9:18pm Edited Date/Time 7/21/2014 9:21pm
benrussell wrote:
once it gets to almost its top speed, the throttle seems to almost disengage (for lack of a better way to describe it). like it is...
once it gets to almost its top speed, the throttle seems to almost disengage (for lack of a better way to describe it). like it is reving really high and then it starts put put puting and then if i realease and repull the throttle it will go back up and then bog down again. even if i keep the throttle pulled all the way it revs high (like it should) then bogs down and then it engages for a couple seconds (and i can feel it accelerating) then bogs down and up and down and up and down. any clue as to what might be causing this?
If you pull the choke and it runs ok, then it's the idle jet. These pw50s have the tiniest idle jet orifice of any bike I've ever seen. I've had to do this so many times with my son's pw over the years. You will need to take some stranded piece of 12 gauge copper wire apart and use a single strand to push it through the jet to clean it. I couldn't even find drill bits or sewing needles that would fit through.
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TbonesPop
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TbonesPop 7/21/2014 9:18pm
7/21/2014 9:18pm
If it isn't the inline filter restricting fuel like the above poster said, then it's a dirty/clogged jet issue in the carb. My son's old PW would do something very similar - I could twist the throttle to about 2/3 or 3/4 throttle and it would be normal - but then I go WFO and it bogged bad, almost would shut off it bogged so bad. This was similar to the wrong main jet on my YZ250. I took apart the carb on the PW and very thoroughly cleaned it out, blowing it with air and in some cases using a needle to punch/"rod" out any debris in the smallest of holes in the carb. After the extremely thorough carb cleaning, problem was solved. You gotta check every jet and orifice in that thing to get it working right. But once you do and keep it that way, it's pretty bulletproof.
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FGR01 7/22/2014 12:44am
7/22/2014 12:44am
I think what you described is normal. My son's PW50 ran exactly like that since brand new. They just don't pull perfectly clean on the extreme top. It's like it's fine under a load but once it gets rolling with little resistance it starts breaking up. It does the same thing on the center stand. If you hold it wide open it will start breaking up but if you make the rear brake drag a little it will clean up. Don't worry about it. No one is going to be wining drag races flat out with all 3 HP on a PW50 anyway.
Paw Paw 271
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Paw Paw 271 7/22/2014 3:45am
7/22/2014 3:45am Edited Date/Time 7/22/2014 3:45am
Yes the PW 50 has an exhaust restriction washer. It is built into the exhaust gasket. It cant be fully removed on some models, but it can't be on others, but it can be drilled out to a larger size. If you screw it up you can just replace the gasket. If this has already been done then you will be lean on the top end and will need a larger main jet.

Paw Paw
Jaze
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Jaze 7/22/2014 4:04am
7/22/2014 4:04am
Same problem here. We just drilled that exhaust restrction away also opened and cleaned carb. Problem solved and never had any problem since that.
Mr. Ted
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Mr. Ted 7/22/2014 6:39am
7/22/2014 6:39am
You may have a partially blocked silencer. If mud or dirt gets packed in there sometimes (they are petty low to the ground after all), it may seem normal until pressure starts to build then bog down. Had it happen to my son's suzuki 50.
project racer 7/22/2014 1:34pm
7/22/2014 1:34pm Edited Date/Time 7/22/2014 1:50pm
If the carb clean does not help, I have had more than one PW that the carbon build up in the exhaust pipe would make them run ratty , never clean out on the top end. Pull the pipe ,clean the exhaust port, (with the piston covering the exhaust port, to avoid hardened carbon dropping into the lower end). Careful not to scratch the piston. Use some Yamaha combustion chamber cleaner to soften the carbon.

Decarbonize the exhaust pipe with an oxy / acetylene or MAP gas torching. Start from the flange heating it cherry red , working your way back. Do the same to the disassembled silencer / baffle. Once it cools , tap it with a piece of wood to jar the carbon loose. Blow out with compressed air.


The baffling system in those pipes has very small holes, and becomes clogged after extended use, especially if the injector is set on the rich side.

You can get about 500-700 more peak RPM out of a PW by disconnecting the ignition control module . The one in the little rubber strap back by the airbox. Doing this will eliminate the start setting requirement on the handle bar switch, not AMA legal.

The exhaust port on the PW is located so low in the cylinder, that the full port area is not even utilized. That's why they take forever to clean out somewhat. Raising the exhaust port, and re-chambering the head, to get the compression back that is lost due to raising the port, will really wake a PW up.
crusher773
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crusher773 7/22/2014 2:19pm
7/22/2014 2:19pm
project racer wrote:
If the carb clean does not help, I have had more than one PW that the carbon build up in the exhaust pipe would make them...
If the carb clean does not help, I have had more than one PW that the carbon build up in the exhaust pipe would make them run ratty , never clean out on the top end. Pull the pipe ,clean the exhaust port, (with the piston covering the exhaust port, to avoid hardened carbon dropping into the lower end). Careful not to scratch the piston. Use some Yamaha combustion chamber cleaner to soften the carbon.

Decarbonize the exhaust pipe with an oxy / acetylene or MAP gas torching. Start from the flange heating it cherry red , working your way back. Do the same to the disassembled silencer / baffle. Once it cools , tap it with a piece of wood to jar the carbon loose. Blow out with compressed air.


The baffling system in those pipes has very small holes, and becomes clogged after extended use, especially if the injector is set on the rich side.

You can get about 500-700 more peak RPM out of a PW by disconnecting the ignition control module . The one in the little rubber strap back by the airbox. Doing this will eliminate the start setting requirement on the handle bar switch, not AMA legal.

The exhaust port on the PW is located so low in the cylinder, that the full port area is not even utilized. That's why they take forever to clean out somewhat. Raising the exhaust port, and re-chambering the head, to get the compression back that is lost due to raising the port, will really wake a PW up.
So if you unplug the control module do you just use run and stop on it? If so I am all over this I'd love for his to run a little cleaner if I can get him running it a little faster I think he'll start making the transition to his KTM more.
Utrider
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Utrider 7/22/2014 2:54pm
7/22/2014 2:54pm
Wow, so glad you brought this up, hopefully someone will be able to chime in on my PW issues. Picked one up for my buddies grandson, the ones I have had have been kick n' go, this one we can't get to start or run.

We have pulled the carb, replaced the pilot jet, cleaned the main jet and circuits. The fuel seems to flow just fine when opening the petcock. Replaced the plug, there was no washer in the exhaust so that wasn't an issue. When kicked it will sputter for a few revolutions, but not run. Checked the switch seems to work as it should, but would be happy to bypass it as we won't be doing any AMA races for a while.

Any and all ideas are appreciated, prior owner said it ran when he put it away.
project racer 7/24/2014 3:32pm
7/24/2014 3:32pm Edited Date/Time 7/24/2014 3:38pm
Utrider wrote:
Wow, so glad you brought this up, hopefully someone will be able to chime in on my PW issues. Picked one up for my buddies grandson...
Wow, so glad you brought this up, hopefully someone will be able to chime in on my PW issues. Picked one up for my buddies grandson, the ones I have had have been kick n' go, this one we can't get to start or run.

We have pulled the carb, replaced the pilot jet, cleaned the main jet and circuits. The fuel seems to flow just fine when opening the petcock. Replaced the plug, there was no washer in the exhaust so that wasn't an issue. When kicked it will sputter for a few revolutions, but not run. Checked the switch seems to work as it should, but would be happy to bypass it as we won't be doing any AMA races for a while.

Any and all ideas are appreciated, prior owner said it ran when he put it away.
You can unplug the connector for the start / run switch behind the front number plate, and see if it will start. If the bike has been wet or washed, water gets in the switch, and they will act like they are on the "start" setting, no matter where the switch is set. You can also squirt a bit of WD 40 in the switch slot to disperse moisture.

All of the electrical connectors on a PW are vulnerable to water. When wet, they simply will not rev / run correctly.

How is the cranking pressure? If below 90 lbs, it probably is not enough to start and run.

If it is an older PW or has a lot of time on it, check for a carboned up exhaust port / pipe / baffle.

Another problem on the PW is sometimes the crank seal behind the ignition goes bad, and won't allow good compression to build for proper running.

A used non runner PW I purchased actually had the seal pop out of the cases, it was sitting right up against the back of the flywheel when I took it apart.


And for what it's worth ,unplugging the ignition control module near the air box will add a bit of peak RPM, but a negligible improvement in overall running characteristics.

For a cheap hop up, run two or three base gaskets, and shave the head .010. This will raise the exhaust port a bit, and make them run a bit cleaner. Too much height on the exhaust port will kill the cranking pressure / compression ,though, so do not go too crazy unless the head is modified accordingly.

120 psi cranking pressure is what a good , fresh, stock PW 50 will put out on a gauge. They will run on 95 psi ,but harder to start, and very dull throttle response. The PW is also fairly prone to seizing the top end. A pinned down ring from a seizure will make for a weak or no run situation.

I used one of those .095 spacer plates under the cylinder base on a PW, modded head, clamp on Uni filter. Was not worth the effort really. Send the cylinder and head to Barr's if you want a good port / head mod.

The low geared QT 50 ring and pinion gear is the best dollar investment to make on a PW. Better low end pull, and only a slight loss in overall top speed. Corner to corner, it works well. Not sure why Yamaha did not spec the QT ratio for the PW , as stock gearing.

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