Well i just got done playing with it... it runs OK on 93octane, but not super great, but... then i decided to try a oddball mix, 110 and 89 (89 being a very prevalent octane rating in the area i will be riding) and it RUNS LIKE A CHAMP... no miss firing or anything of the sort, top end is strong, i put a new plug in and did a "plug chop" going from idle to top speed. plug looked PERFECT, and its hotter than a bastard ehere today. If it was detonating, it would just sputter and pop if i jumped into the throttle right? cause when i did that, all it did was run like a rabbit with a rocket up its rear!!!

 

Detonation or pinging sounds more like a knock than a ping. It's pretty obvious that something is wrong when it's happening because the noise is out of phase with the normal engine noise. It can do it at any engine speed (depending on what fuel circuit is running lean) but usually happens after the engine is good and hot.

BTW if you did a plug chop from idle to full throttle, you only got a plug reading at full throttle. In order to check your jetting at 1/4 throttle (pilot jet/air screw) run a new plug at 1/4 throttle for a minute or so, then hit the kill switch before the rpm drops. Same for 1/2 throttle (needle) and full throttle (main jet). You want a nice caramel color. Read this. There's also a good fuel article on that site.

 

I found out why it probably istn detonating with the fuel that im using.. I did a compression check, and its only 120!!!.. i honestly cant believe the bike runs this strong with compression like that... im gonna try and nurse it through 4th of july weekend, then do a whole new top end.

 

what compression piston should i get.. i plan on running a weisco.. i would like to be able to have good power running on 93 octane...

 

Wiseco only offers one type of piston for the 87 and rumor has it that it has been or will be discontuned as it is model year specific. Unlike a four stroke, with a two stroke compression is typically adjusted by changing the heads dome volume. You may just need a set of rings if the bore isn't too screwed up.

 

and when you did your compression test did you hold the throttle open and kick until it wouldn't go any higher?

 

I held it open, and kicked it 8-10 times each time.. If the wiseco is going to be discontinued, is there anyone else makeing anything decent for them??? i really dont want to do stock.. the motor is sposed to be fairly new, but im planning that its gonna have to have another .10 taken out, to make it .30 over... who makes a good piston for that type of size... and also are u saying that the piston has nothing to do with the compression of the bike???

 

Not saying the piston doesn't have anything to do with compression, just saying that compression is normally adjusted by rechambering the head. This is because the the shape of the head has a lot to do with how a two-stroke runs. Also higher compression is not always better if you like top end power. Check out www.eric-gorr.com there is alot of information in the tech articles about how two-strokes work.

As for pistons, you can still get the wiseco. Go on ebay and look under the seller atvaddiction.com. You may want to check with the guy you got the bike from cause if it has a stroker kit it might not use a stock type piston, try to find out who did the engine, ie Duncan, CT, FTZ.

I've read something about using a repinned YZ piston, but I don't know the details.

 

Cool i'll have to check that out!!!