Yamaha PW50 questions

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Aug 3, 2005
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#1
Go easy on me please...first posting! And yes, I really should buy a manual.

I'm doing the top-end on my Son's 2000 PW50. I've got a Weisco kit.

What should I torque the head bolts to? Which way should the arrow point on the piston? The stock Yamaha piston arrow was pointing down (forward?) but that doesn't seem right to me. Finally, what is the break-in procedure for a new top-end on a PW? Any other hints or advice would be greatly appreciated.

Oh, has anyone ever put a lower (numerically higher) gear set in their PW? What does it cost, where can I get one? Even with the throttle adjustment screw almost all the way in, the bike is too fast for him but then it won't climb any kind of hill either. Thanks.
 
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#2
Don't waste any money on the PW50. Just use it to teach your children how to ride then move on to something better.

If the bolts are 10mm..the recommended torque is 25.
If the bolts are 12mm..the recommended torque is 40.

The arrow should point towards the exhaust side of the engine. Good luck. :cool:
 

Jasle

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#3
the bolts should be 5mm. the spec is 9.8 foot/lbs or 144 inch/lbs if I remember correctly. could be off a bit but definetly close. done several in the field without a torque wrench and they were fine.

the arrow should always point to the exhaust port. Look at the piston. if you put it in backwards the ring opening will face the larger exhaust port and the rings will hang up in the exhaust port causing serious damage.

just do one or two heat cycles and your fine. its really important to clean the mud off the bottom of the cylilnder regularly to keep the area around the exhaust port fried. they overheat there since they are air cooled and collect mud there.
 
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#4
Thanks guys. The bolts are 10mm and anything more than about 10ft/lbs just turns the entire shaft.

It's back together now (that last wrist pin was a mother) and running. I need to work on the mixture though as I think it's too lean by the plug reading.

Adjusting either carb screw seems to do very little to change the tune.

Out of curiosity, I checked the compression reading before the top-end. 90 psi. Now it's about 97 psi. I don't think the old piston and rings were really that bad but the bike would not run past 1/8th throttle at all. Just bogged horribly. Now it seems back to normal.

I've ridden it twice with light throttle on relatively flat ground for about ten minutes each time. Probably time to let it rip!

Thanks again...
 

Jasle

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#5
hh65flyer said:
Thanks guys. The bolts are 10mm and anything more than about 10ft/lbs just turns the entire shaft.

It's back together now (that last wrist pin was a mother) and running. I need to work on the mixture though as I think it's too lean by the plug reading.

Adjusting either carb screw seems to do very little to change the tune.

Out of curiosity, I checked the compression reading before the top-end. 90 psi. Now it's about 97 psi. I don't think the old piston and rings were really that bad but the bike would not run past 1/8th throttle at all. Just bogged horribly. Now it seems back to normal.

I've ridden it twice with light throttle on relatively flat ground for about ten minutes each time. Probably time to let it rip!

Thanks again...

Well the nuts are 10mm...thats what size socket you need. The bolt size is actually the size of the dia of that stud. So looking at ours it looks like a 6mm.

around 100 is what I'd expect. 120 with a milled head. after two heat cycles you should be ready to rock.

The air screw on the side does not do much until you get the correct main jet. these carbs are wierd in that the air screw affect the entire range of the carb where most bikes it just affects from idle to 1/3 throttle. not sure your altitude but a 67.5 should work pretty good unless your really high then a 65.
 
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#6
Thanks Jasle! That was very helpful.

I finally broke down and got a manual (on CD, very cheap).

You're right...nuts, not bolts!

I'm basically at sea level, I'm not sure what jet is installed but she seems pretty lean to me and I don't want to risk anything. I'll pull it apart tomorrow and check.

Again...thanks.
 
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