300 won't idle. Please help!!

[gasser]

My son's bike has much the same problems you describe - smokes badly, loads up on the bottom, and has to get on the pipe to keep running. His bike is pulling trans oil into the engine somehow. I suppose it's a bad crankcase seal on the right side or perhaps a bad case gasket (is that possible)? Anyway it is definitely pulling oil out and burning it. A 2-3 hour ride burns about half of the tranny oil.

[Jakobi]

Use a 14mm open ender and unscrew the whole choke plunger. You'll see how it works. Basically just a shaft with a plunger on the bottom. The plunger is a rubber seal that closes the choke circuit. As you pull the choke up the circuit opens. If the rubber is perished, chipped, cracked or warped out of shape it will won't work as it should. If its completely damaged it will be like always having the choke on, pulling the choke on will have little to no effect, the bike will run really rich and fuel econonomy will suffer.

[hannesd]

i personally,wouldn't touch jetting if your idle progressively got worse.
if the conditions are still the same, id look for wear on something like indeed choke rubber or maybe crank seals or even reeds...
alltough with broken reeds i didn't really have a flat spot in my case,only no idle.

hannes.

[hannesd]

FYI : i've had a mopet once that had the rings broken in 4 pieces (both) and it still ran, alltough i had to rev it to the moon
that's how good a 2 smoker is

[stemplin]

I went ahead and pulled my jug and there was some blow by that couldn't be seen from the exhaust outlet. Cylinder still looks good with visible cross hatch marks but ring end gap measured 0.95 mm so I guess it's time for a top end.

The piston that was in there is marked "D 71.97" and the back of the jug is stamped "B". Any suggestions on a place to source a good top end kit? I've found a complete Wossner "C" kit with gaskets and everything for $239.00 on Ebay.

Any thoughts on the D piston would be greatly appreciated.

[Jakobi]

Originally Posted by stemplin

I went ahead and pulled my jug and there was some blow by that couldn't be seen from the exhaust outlet. Cylinder still looks good with visible cross hatch marks but ring end gap measured 0.95 mm so I guess it's time for a top end.

The piston that was in there is marked "D 71.97" and the back of the jug is stamped "B". Any suggestions on a place to source a good top end kit? I've found a complete Wossner "C" kit with gaskets and everything for $239.00 on Ebay.

Any thoughts on the D piston would be greatly appreciated.

Nice find. How'd the D piston looking? Does it show much wear around the skirts? Not sure where you'd get a replacement D from. Maybe ask around some of the places selling the kits and see what they say. They might be able to order you one in, or possibly suggest just running a C. I found the Wossner A I dropped in my A cyl was a better fit than the Vertex A I pulled out at 75hrs. The rings were still only 0.4 and 0.5mm respectively. I pulled it down due to piston slap. Go figure. The Wossner now has 75hrs on it and sounds much better.

[stemplin]

The skirts actually look really good, not many wear marks at all and i wasn't hearing any piston slap. I've been reading that different manufacturers piston sizing varies. I was thinking of using the wossner c kit but I have no idea what brand the current D piston is.

[Jakobi]

You could always just try and source a set of rings for it, but might be hard not knowing what brand.

If the nikasil is still in good shape then odds are the C will fit nicely in the B cylinder. The difference between a C and a D is 0.02mm. If the D had of been slapping or showing wear on the skirts you wouldn't even consider down sizing.

The right way to do it is to take it somewhere with the equipment to have the piston to bore clearance measured.

[stemplin]

Does anyone know if the wossner's have any identifiable markings on them. I know I've seen "w" on wisecos before but all I can find on this one is the "d 71.97" and and arrow towards the exhaust port.

[Jakobi]

Originally Posted by stemplin

Does anyone know if the wossner's have any identifiable markings on them. I know I've seen "w" on wisecos before but all I can find on this one is the "d 71.97" and and arrow towards the exhaust port.

The S3 Vertex I have here has its brand printed on the top along with size and arrow.

I can't remember what my Wossner had. Looking at pics it appears they have a part number only.