'02 YZ85 chronic plug fouling...help

[john_bilbrey]

OK, my stepson's YZ85 is a chronic fouler of plugs. Been running BR10ES/EG in it. Bike shop recommended the non-resistor plug, saying that could be causing part of the problem with fouling plugs. Since we bought the bike used a little over a year ago, I'm not sure about jetting or anything else for this one. It came from a "race" family, so I'm pretty sure that the jetting is correct. The bike has a PC pipe and silencer, and I added a flywheel weight to tame it a little to make it more woods-friendly.
What are the recommended jets for this one, and the proper plug? I don't have any of the manuals or anything for it. Could the wrong plug be the cause of the fouling? I'm running Bel Ray H1R @ 40:1, BTW.

 

[Patman]

I'd start by getting a factory manual for the bike, they are worth their weight in gold many times. Next pull the carb and see what brass is in the carb and where the needle is set. This jetting might have worked for the previous rider because they used a different mix or fuel type. Also pick up the plug specified in the shop manual even if it is a resistor plug, it's the correct plug. When you put the carb back together be sure and clean it well and check the float adjustment. Now you will know what you are starting out with. While you have that spark plug out getting swapped for the correct one run a compression test on the top end. If you don't have the tools or ability to do this get it done at a local shop with a good rep. These little bikes go through top ends a lot faster than most people think and low compression could be causing your plug fouling as well..

 

[john_bilbrey]

OK, thanks for the reply. That was going to be my first step, to see what was actually in there and go from there. The previous owner was using it for MX, and this is a woods bike now. That could explain some of the differences as well.

 

[W00TsP0P]

search for (yz plug) this topic comes up many times.
But surley get the owners/repair manual. this should always be the first thing you buy for your bike!
it does prevent lots of head pain

hope this helps

 

[wade450f]

My sons 03 yz85 was jetted rich and the FLOAT setting was incorrect.
used to foul plugs all the time until I adjusted the float.


also I went to a small front sprocket for woods riding.
This keeps the revs up and speeds down which helped a lot.
and its easy to change back when the speeds come up

 

[john_bilbrey]

He is due for chain/sprockets, so I may go down one on the front when I change them...we added the biggest flywheel weight that Steahly had, which made a huge difference in rideability for him.