RM85 Fouling Plugs

6 replies to this topic
  • MxWrench91

Posted May 23, 2009 - 02:58 PM


Hey my little brother just bought a 2006 RM85 and it's fouling plugs like crazy. I just checked the reeds (everything was good), cleaned the carb (set the float), cleaned/oiled the air filter and installed a new BR10EG. Bike's running 91 octane mixed with full synthetic at 40:1. I taught him the proper way to warm up the bike also. When warming the bike up if you blip the throttle farther than 1/4 or right when you go to pull away, the bike will foul the plug. Any idea's on what I should check next?

  • zig06

Posted May 24, 2009 - 06:51 AM


Is your little brother a fast rider? If he's going kind of slow or riding in some very tight areas, you should consider running a hotter plug. If that doesn't do it then install a smaller pilot jet and lower the needle to the second or even first clip posistion.

  • killerdwarf77

Posted May 24, 2009 - 07:54 AM


A 10 is a pretty cold plug. Install a #8 plug for a beginning rider, make sure the air screw is set properly. Raise the clip on the needle as Zig suggested.

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  • Treesmacker

Posted May 24, 2009 - 09:56 AM


We run a BR9EIX plug for woods riding and it works great.
pj48 mj122 (125 when below 50degs) stock needle NAAH clip#2
NAAJ for woods

  • MxWrench91

Posted May 24, 2009 - 02:38 PM


He's just coming off a XR70, so he's pretty slow. Doesn't hit the powerband much. I already guessed the pilot was too big. I turned the air screw out another full turn, and raised the clip on the needle. Still fouled, so I threw in a BR8EG out of my 125. So far it seems to run good.

  • hbidad

Posted May 24, 2009 - 08:40 PM


We run a BR9EIX plug for woods riding and it works great.
pj48 mj122 (125 when below 50degs) stock needle NAAH clip#2
NAAJ for woods

Man, these jets are driving me insane. I ran 130 and started to dome in the piston and you could see a large burnt oil spot under the crown when it got cooler out (60 degrees). The plug and piston was black, no indication it was running lean besides it was very boggy until it warmed up. I thought the temp caused it.

I rebuilt the motor, went to a 125 (I know, leaning it out) with a new SST pipe and ran a single race (fmf says a 122 mj). Same deal, piston crown domed inwards with seizure marks on the intake side. Then again I race flattrack and those two tracks were rather long (1/4 and halfmile).

I put a new piston in and went way up to a 135 which seems rather rich.

  • LongW8

Posted May 25, 2009 - 11:49 AM


I had the same trouble with my sons RM85. My son was also new to the bike and rarely got on the pipe much. The RM85 is a great bike for the beginner rider!

Did you buy the bike used? The son of the guy I bought ours from raced the bike. I suspect that they had an aftermarket pipe on it before I bought it. When they sold the bike to me they swapped out the aftermarket pipe and put the stock pipe back on. I'm sure the wanted to resell the aftermarket pipe. They must have rejetted for the aftermarket pipe and never returned the jetting to the stock settings. Check all the jets and return to stock. My manual says:
Main jet=#125
Slow Jet=#50
Jet needle=24NAAH.

This worked for us.


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