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Pw50 running backwards

By Cossie331bhp,
in Yamaha 2 Stroke

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Cossie331bhp

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Posted

Hello all

New ish here so please bare with me.

I've just picked up a pw50 none runner (no spark).

I changed

Spark plug

Spark plug cap

Cdi

Stator/magneto (now sparking) none genuine part.....eBay

Started kicking the bike got some good back fires but then she started. Only problem is the engine is running backwards.

I've done lots of searches but the results have not helped me.

I believe it's ignition timing but it's none adjustable?

On one occasion when starting the bike the engine did run forward but did seem abit flat when you revved it.

Any help would be greatly appreciated

Thanks rob

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Cossie331bhp

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Hi all

1. What is event timing?

2.i did compare all parts and all looked the same. I ended up removing both the coils and the pick up sensor and mounting them on the original Yamaha back plate. The bike did run forwards once but power seemed flat.

3. Yes I'm starting the bike with the switch in the start position

4. Before letting my boy ride backwards I dicided I should go first. Bad idea!!!

Thank you for all the replies so for

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Grand Master

rjpjnk

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Posted (edited)

An interesting thing about 2 strokes is that they can run just as well in either direction. Since there are no valves, the cycles are completely symmetric. I believe the only thing that causes them to have a preference to run in one direction over the other is ignition timing.

 

I would guess that somehow when you replaced the stator coil something happened to significantly retarded the timing past TDC so that the engine prefers to run the other direction.

 

The PW50 doesn't have a clutch. But if it did, I bet you could pop start it in the direction of your choice.

 

EDIT: Can the coils be installed backwards?

Edited by rjpjnk
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Proficient

CJH

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It does sound like timing, but I have gotten burned on aftermarket electronics in the past. One of the non oem parts could be defective. Check out ski doos r.e.r. Concept if you get a chance, the engine runs normally for forward direction and when you press the reverse button the engine slows down to almost a stop and starts back up spinning in the opposite direction. That is all controlled through the Ecm.

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Cossie331bhp

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Hi all.

Done some more work tonight.

1. I slotted the holes in the stator plate so I could advance and retard the timing by around 10mm each way

2. I turned the stator around 180 degrees refitted.

3. I swapped both coils around on the stator plate.

None of the above helped and all made the engine run backwards.

Also swapped the cdi. Still no joy???????

I think I will have to try get a genuine stator

Any more ideas anyone

Thanks rob.

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Experienced

bk29

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I really don't see what the problem is, if your child can ride it backwards they'll be awesome.

That's a great idea. I can't ride backwards but I feel like might only be because I learned going forward. If you start out going backwards it might be just as easy as going forward. When your kid is riding his pw backwards around the beginner track everyone is going to stop what they are doing to watch. Imagine how proud you will be.
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Grand Master

numroe

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Interesting issue.

So does the kick starter turn it forward then on last forward rev it fires into reverse? I presume so. Doesn't that suggest that (in the forward direction) it has excessive spark advance?

When you removed the plug to check spark did you see just one spark per rev?

Remove the rev limiter box and start it with the switch in run position. Just to see what happens. I always had that box removed.

Also start it without the muffler in case of excessive restriction. Or clean out and drill out the muffler core a bit.

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Grand Master

rjpjnk

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Hi all.

Done some more work tonight.

1. I slotted the holes in the stator plate so I could advance and retard the timing by around 10mm each way

2. I turned the stator around 180 degrees refitted.

3. I swapped both coils around on the stator plate.

None of the above helped and all made the engine run backwards.

Also swapped the cdi. Still no joy???????

I think I will have to try get a genuine stator

Any more ideas anyone

Thanks rob.

 

Is there any chance the flywheel is rotated on the crankshaft due to a sheared key?

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Ron W

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I was riding my old Husky one day pulling ribbon after desert race. I would pull up to a ribbon grab it and stuff it under my shirt.

As I was stuffing a ribbon my bike nearly stalled. I quickly grabbed the throttle and kept it running.

Problem was as I tried to pull away, the bike felt like the back wheel was stuck in a hole. I tried again to take off, but the bike wouldn't move forward.

I looked down a the back wheel as I released the clutch and it was running backwards. I shut it off and restarted it and rode away.

Realized shortly after that my rod bearing was so loose it was letting the piston dwell at top dead center to long and it could fire backwards at low rpm's.

Not saying that's your problem, but it is a possibility.

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