PW80 Question

[Rhodester]

I'm in the process of buying a used Yamaha PW80 ('99). At 45 degrees and 2600' elevation it's 4 stroking (sputtering) in the upper RPM range. Is this a factor of restrictive exhaust or porting for bottom end performance (ie. by design) or am I dealing with too rich jetting which will clean up by leaning the main jet?

 

[joereitman]

Bike has exhaust and porting for low rpm, plus there is a rev limiter that makes it intermittently cut out at high revs. Mid range can be helped some by leaning needle 1 clip position and drilling out the welded in restrictor in the mouth of the pipe. I have read only way to bypass rev limiter is ignition from 1980's pw.

 

[KCL]

We had a PW80, Yah the restrictor in the exhaust needs removed, but those bikes are set to run pretty richly. Removing the autolube and going to pre-mix you can lean out the gas/oil concentration and improve throttle, along with the carb needle setting. The air filter is another sore spot. the airbox is very restricting due to it's position behind the front tire. You can drill some holes to improve the air intake, but we went to a K&N coming right off the carb. We never messed with the ignition, but I'll bet that would help. Also, FMF makes a pipe for this bike, the stocker is kinda on the flat side.

 

[scairns]

My son's 91 PW80 had the same condition.

I removed the norkel at the top of the Air Box (rubber) and that did it.

Try a smaller front sprocket, hugh improvement in power delivery.

Search through this form there is some good info on PW80's (free mods)

Great Bike Cheers !

 

[scairns]

Need Spell Checker Bad ???

snorkel

huge

?

 

[joereitman]

I made a huge leap on rr sprocket- 32 to a 48. World of difference. I also disabled autolube by removing gear from pump. Run 32:1 MX2T, same as my KX. Have not done snorkel removal yet.

 

[viking20]

When we ran a pw 80, we had to run stock engine,but I know people had good results with holes in the standard airbox.We used a 100 main jet most of the time with premix in the tank.Sometimes we could run a 90 main in warm weather.On our very short tracks for the kids we used 15-43 gearing,front sprockets fits from the kx 60,i believe.

 

[Rhodester]

I'll try opening up the air box, raising the clip 1 notch (to #2), installing a 14 tooth countershaft sprocket (from a 15), and dropping the main 2 sizes to a 115 (for a start). I think I'll keep the autolube for the time being, unless you think it makes a significant difference in how it runs to go with premix. Does any one make a sock type air filter that will fit the carb? Thank alot for the tips.

 

[joereitman]

runs a lot cleaner on premix

 

[Rhodester]

Just discovered that my yamaha dealer only lists a 130, a 125 and a 120 main jet for the pw80. I put a 120 in to start with. Does anyone know of a source of leaner jets for this little mikuni carb. I may reconsider running premix. If I'm thinking right that alone will lean the mixture a little (by diluting the gas with oil).