PW50 running backwards???

It's been awhile since I've been on here, but I feel I've gave this question a decent search already.

My daughters birthday is in 1 week and her new pink plastics just arrived for her "new" 1999 pw50. I picked this bike and a parts bike up off of a guy that had "rebuilt the topend as well as replaced the wiring harness." I've sorted out many problems and finally got it to start. The bike runs WTFO backwards!!! When I rotate the kick starter the rear tire rotates forward, but once the bike fires the rear tire spins backwards. Could this be a timing issue? I've did some searching and it seems that the pw50 can't be timed wrong from what I've read. Also, I finally fixed the non-working throttle cable and now with the air box off I can watch the slide move up and down within the carb, however it is still running wide open no matter what the throttle position is. Any ideas would be greatly appreciated.


So it starts normal more or less but then switches and runs ass backwards?

If I got that right I would think that the piston was installed upside down or backwards. depends on how you look at it. If I were in your shoes I would take the top off and have a look at the piston.

Or you have some odd carb problems. maybe loading up the motor with fuel and then backfiring and running itself WO until fuel is consumed.

I'm sure someone more knowledgeable than myself will chime in for you as well.

Hope it works out and to here back. Regards,

Wow, I start to write and then just sit here and stare at the page. I have no idea how a 2t can run WFO backwards. The best thing I can say you need to jump on this thing and have someone video you riding it backwards.

Ok - Here is what I'm thinking:

  • Somethings messed up because I don't think Ive ever been able to flip the kick start and have the bike turn over in the other direction. I actually just looked at our PW (2002) and its a left hand kick with the kicker behind the foot peg and you push down. To flip it on this model I think it would just hit the footpeg?
  • The carb slide is down and the bike is WFO? Massive air leak? It has to be if the slide is down and that thing is WFO. Does it run WFO from when you start it or does it do it after you crank the throttle?

Make sure the carb slide is going the whole way down. I just replaced the throttle cable on ours, and I put a little nick in the slide and it would hang up partway down. I just filed it off. And make sure the carb cap is on right. It can be on cockeyed and and the screw will still tighten. It does not take much throttle to make the bike run WFO on the stand.

The crankshaft could rotate in either direction and a 2T engine could work if the spark timing was right, but the spark timing only works one way. And the engine would not start and change direction by itself. Not enough compression to overcome the crank momentum.

I think you have some kind of transmission issue making the wheel run backwards, like the clutch is loose and fluid drag is rotating the wheel the other way.

you got one of those south of hte border PW50s.

i guess you would have to think of this in a logical pattern. if the crank is rotating backwards, would it make the bike run in reverse? yes/no.... is it possible for it to rotate backwards....yes/no

if the above checks out, i would look at the tranny and gearing.

I'm thinking that it could be "loading" up on fuel, backfiring, and then running itself in reverse consuming the unused fuel from the pipe.(kind of like a 4t dieseling) But hearing of one running in reverse is a first for me. Like I said, first stop for me, would be to check the piston/jug/head. The prior owner said he rebuilt it, and so I would naturally think that's the most likely place to have an issue.

I had a friend back in the '70's that had a mini enduro that he could get runing backwards by pushing it backwards and popping the clutch. He jump on and ride it that way.

Check the flywheel key.

Thanks for all the help so far. I was thinking today at work that maybe it could be an issue somewhere in the drivetrain? Maybe a gear with the teeth facing in the wrong direction? I've never had a driveshaft bike so I don't know if that could be part of the issue or not. The bike has backfired a few times on the kicks that didn't get it started... perhaps that is the issue. Whats my best solution there? I'm fairly certain the carb is in the ballpark of being correct per the owners manual settings. Just to clarify.. I don't believe its just loading up and running off unburnt fuel in the pipe, it will run in reverse til I switch the engine off. If I've got enough battery left on my phone I'll try to get a video of it tonight.

Tomsti: I had the same thought you did... ride it in reverse! I did that the first time I got it to actually fire after buying the bike, my foot slipped off the peg during the ride and caught the kick start lever, and in that action actually jamed up the kickstart mechanism and had to replace it. Was fun... but not the brightest idea:bonk:

Another update...

Pulled the cover, and the generator/flywheel or whatever it may be called on this bike has an arrow on it... rotates backwards as i rotate the kickstart lever downward. Any ideas what the problem may be? I don't have a flywheel puller so I won't be able to remove it until tomorrow. In the parts diagram it appears that the crank is 2 pieces.. could the guy have assembled it incorrectly and this be the source of my problem? I also removed the exhaust and fired it again to make sure that a clogged exhaust system wasn't creating too much back pressure causing it to backfire.

So if you're looking at the stator, does it rotate left or right? if memory serves me it should spin clockwise.

It might be spinning in the right direction and only seem backward to you. Can you or are you able to pull the cylinder head? should just be 4 bolts. See if you can determine if the piston is installed backward.

Tomsti already hinted on this but is it possible that your kick starter is on backwards? I'm not intimately familiar with this bike, but I would think it wouldn't be possible? ? ?

Also look at the key that holds the stator on the crank. If its off or slipped it could cause your problem.

I rember the old Kawasaki two stroke street bikes would ocassionally run backwards. You could actually push start them in reverse and they would be going backwards. Also I had a YZ80 "B" model we converted from points to an after market electronic ignition. It would dang sure run backwards we had a blast holding front brake on and spinning dirt the wrong way :thumbsup:

I also think some old school two stroke outboards had a system that instead of a geared reverse they would simply run backwards using a switch postion or some kind of control. I bet lawyers got paid on that one.......:confused:

A partially sheared flywheel key could alter the timing enough to cause the engine to cough and then run backwards. Need to pop the flywheel off and take a look.

If you see the rear wheel turning forward as you operate the kickstarter, then it is doubtful that you have a gear/tranny issue.

The runaway engine is probably a different issue. A massive air leak, such as a bad crank seal, will do this exactly.

A partially sheared flywheel key could alter the timing enough to cause the engine to cough and then run backwards. Need to pop the flywheel off and take a look.

If you see the rear wheel turning forward as you operate the kickstarter, then it is doubtful that you have a gear/tranny issue.

+1 sounds like the simplest and best explanation to me.

Could the flywheel be from a different bike (cheapo Chinese maybe?), hence turning in the wrong direction of the arrow AND running the wrong way?

Does your parts bike have a flywheel? Compare them.

i am staying tuned in to hear the results.

Any non rotary 2T can be run in reverse, you just bump start it backwards, it's always been like that, motors don't care which direction they turn in.

The reason it's "dieseling" is because your timing is never set to fire at TDC, rather sightly advanced so once a motor runs backwards, your timing will run slightly retarded.

This shows your timing is still ok, however, it's still a mystery as to why the motor fires up into a backward rotation.

You know how 2T snowmobiles can run backwards and it's actually a reverse's a computer controlled timing related sequence, the computer shuts the motor down, when it senses RPM to be almost stopped it fires the motor again but changes the timing to 20 degrees advanced (BTDC) which pushes the con rod back in the direction it came from, reversing the motor, then changing the timing to be retarded (from a forward rotating aspect) for the duration you will be using reverse, therefore reversing the entire drivetrain rotation and timing to give you an actual reverse.

On a dirtbike, if you hold the kill switch but let it go again right before your engine stops rotating, sometimes this kicks your motor into reverse accidentally, it's a very small window of opportunity for this to happen but the possibility is there.

A backfire can also cause this but it is VERY rare, so your repeated reverse issue is likely the cause of something else.

The flywheel is a prime suspect (key may be sheared) as well as a bad crank could be your issue.

It's a typical crank you'd find on any dirtbike, but that's not to say Crank may be out of balance or have bad big end bearings which cause a binding issue on the upstroke.

Likely, your issue is with one of these two suspect items.

As for your carb, it does sound like an air leak between the carb and cylinder BUT - get your motor rotation figured out first then see if things don't correct themselves automatically on the carb.

Alright, you guys have gave me a lot of good advice. We have been without power here for a day and half with another day or two ahead of us so I'm left to using my phone to make an update. Turns out the flywheel/magneto was the issue. Found the stock one in the parts box that came with the bike. The arrow rotates in the opposite direction(the correct direction) and the magnets appear to be shifted just slightly in relation to the keyway. This solved the timing issue and the rear tire now rotates forward when the bike is running. Now onto the wide open throttle issue. The slide is down so I'll begin chasing after an air leak.

crank seal....stator side

Problem solved. The WOT condition seemed to be caused by a bad seal where the jug mated to the case. With it running wide open i noticed fuel bubbling out, so I pulled it apart and gave it some gasket sealer. Tuned the carb and it's running great! My little girl loved riding it with me "I wanna ride! I wanna ride!" Her birthday is tomorrow so I told her I'd take it to work with me and see if I can find anyone that might want to trade me a pink one for "my" blue one. The new pink plastics are on it now that shes in bed, and she'll be shocked to see it tomorrow!

Thanks for all the help

Create an account or sign in to comment

You need to be a member in order to leave a comment

Create an account

Sign up for a new account in our community. It's easy!

Register a new account

Sign in

Already have an account? Sign in here.

Sign In Now