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Only $10 for all 2024 SX, MX, and SMX series (regularly $30).
Do this with one ring at a time. Don't try to stuff them both in the cylinder at once.
More times than not, even when bored / honed to spec, the rings gaps will lean toward the loose side of spec.
.006 - .014 is the spec for PW ring end gap.
But in the end, if there is too much piston to bore clearance, ring end gap is irrelevant.
I prefer the cast Yamaha pistons over the Wiseco. Wiseco calls for a bit more piston to bore clearance , initially. They tend to be a bit noisy on start up. Let it warm up for at least 5 minutes with a Wiseco before every ride. They are my last choice if I have one.
Be sure you have tried the cheap , free stuff first before you spend any money. Did you try it with no pipe ? Check the piston arrow ? Rings are not stuck in the grooves ? Can you keep it running on starter fluid ?
Chances are, if it will stay running on fluid, it has enough squeeze to run on gas.
$80 is not too bad on a complete piston kit with all you mentioned. My dealer would be at about $70 for the same, as I get a small discount.
I have a complete OEM Yamaha cylinder and top end kit, new in the box. If interested I would let it go, but sure would hate to see that not fix things.
The Shop
I think your problem is the reeds also. Take off the intake manifold, and flip the reeds for good measure.
I've got a first year PW, 1981, on the original bore and it still runs after being mercilessly beat by 2+ generations of punk-ass kids even before I got it. It had a pine needle stuck in a reed, which was -of course- the last thing left to check when it wouldn't start. But it runs great even with low compression. They're not race bikes.
If the reeds are good, then it's the fuel system, which luckily will already be off the bike. On my bike, the carb is so close to the fuel petcock that I had to run the fuel line through a spring to keep it from kinking. Also, drain the bowl a few times to make sure you're not getting water in there. A small amount of water could be plugging those tiny jets. Drain from the bottom of the bowl (the screw next to the tube) and drain it onto cement so you can see what comes out. Water will not soak in like fuel.
Good luck!
Is the little plastic insert in the front of the carb where it slides onto the intake in good condition ?
If the bike was always hard to start, on the original top end , as well as the kit top end, seems like there may be something else going on.
Unless both top ends have so much piston to bore clearance that neither develop good cranking pressure.
The plastic insert on the carb looks to be in fine shape too and fits pretty snug.
I really appreciate all of you guys ideas and help!
I used one of those 3 mm rev plates that fit under the cylinder, and took .125 off the top deck of the cylinder. The exhaust port was too high when this was installed, and cranking pressure was about 105 psi. Took .020 off the head, and got about 115 out of it.
More hype than hump from that deal. I should have just raised the exhaust port myself by about 1mm, and had the head cut and rechambered.
It was not much better than a stock PW . Live and learn. The best thing I found to wake the PW up was a set of QT ring and pinion gears. A bit lower ratio, pulls better from low end . Still have the setup around here somewhere.
I've heard about the QT ring gear swap. Maybe I can take that off your hands one day if I can ever get this baby running. First things first though. Thanks again.
I'm out of ideas without being there to look at the bike. There's not much to 'em.
Pit Row
Thanks,
PS , I'm following your tread closely as my pw not running too great either. MIne will run though, just have to keep it running with the throttle cause it won't idle. That's doesn't affect me but it's making it hard on my 4 year old grandson. I fiddled with the stupid ass carb and it appears fine (jets all look good). I just bought a new carb off ebay. Haven't installed it yet though.
I got a question for one of you though, when i change out the carb it has the hose that goes from carb to oil injector pump looks to have some form of band clamp. How does that come off? It doesn't appear to just slide off.
Make sure you use the both QT ring and pinion gears, as they both have different number of teeth to achieve the lower ratio than the PW. You can use a spark plug wrench to remove the pinion nut in the housing. There is also a primary gear that is sold that lowers the ratio to QT spec. It replaces the stock PW gear on the clutch side of the crank.
The little clamp on the oil line has a split in it. Just find the split, gently pry it open, and slide it down the line. Careful ,they are easily distorted.
I considered the primary gear, but lucked onto a junker QT ,and snagged the differential out of it. Stabbed in a PW axle, along with new bearings, seals, brakes. The rear diff / housings can be swapped in about 10-15 minutes .
Set aside a good hour for the primary gear swap, more if you have never taken a PW apart.
Anyway, I installed my primary gear today and have a couple questions. The old primary gear that came of had like metal spacer/thingy with rubber in it kinda like a balancer on a car. The primary gear I installed was one I bought second hand off ebay. It was a solid gear with no way to reuse the spacer/rubber/thingy with it. Is this the way most aftermarket gears for these bikes are. My gear did have one less tooth than the original so I assume it's at least different.
Yeah the way you have to pull the engine out this thing to get clutch cover is pretty stupid. But like anything else, it's been done once now so it will be easier next time.
Thanks
Hundredths vs Thousandths.
If you suspect you still have an air leak some where, the best thing to do is a leak down test of the engine assembly.
Pull the engine out of the frame, pull the stator , flywheel, and clutch assembly , so that both main seals are visible.
You will need to make a plug / plate to seal the exhaust port, a plug for the intake, which will need to be plumbed for a Schrader valve, a small hand pump, low pressure gauge, a vacuum T, and some vacuum line , to make a pressure tester.
You basically want both intake and exhaust ports sealed tightly, using the Schrader port to pump about 7-10 PSI of air into the engine. T the line into the low pressure gauge to monitor pressure / leakage. Leave the spark plug in it, making sure it is also tested for leaks at it's gasket.
You want the piston at bottom dead center as you pressurize the engine.
At 7-10 PSI , the engine should hold this pressure for at least 3-5 minutes without more than a small percentage of loss.
While under pressure, spray every seal, gasket mating surface, case half mating surface on the engine with a soapy water solution, and check for leaks. Soak it down good.
If the engine holds pressure, and no signs of a leak are detected, re -check your piston to bore clearance.
Or just pop a clutch side crank seal in it, go back together , and see what happens.
If low gearing is the goal, the shorter the overall tire height , the lower the overall final ratio will be. Taller tire, taller overall ratio.
Gharmon: I wouldn't worry about the cush vs the non-cush drive. It makes no difference for a dirt bike. I do wonder about how one gear can be swapped out for a different size without the mating gear being changed. Seems like the teeth won't engage the way they were designed to, due to one smaller gear. I guess it doesn't matter too much in such a low HP machine.
Keep us posted and good luck to you both!
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