Proper fuel mixture

[2000 RM 85]

My son's RM 85 seems to foul plugs more frequently than I think it should. I think it is a combination of his riding ability and fuel mixture. His skills are improving but I wonder if I could tweak the fuel mix. The manual recommends 20:1 which I think calls for a lot of oil. Seems like going to 32:1 would help fouling. We use Yamalube. Any suggestions?

Thanks!

 

[WillyM]

If you do what you are thinking you very well could foul more plugs than now.
Search on this site for jetting tips.

 

[2000 RM 85]

I understood plugs would foul when the engine was lugged too much and/or if the fuel mixture had too much oil? The bike is stock, does it really need to be re-jetted?

Thanks for the input WillyM!

 

[kxmike]

go to 32:1 with that yamalube 2r. i use to use it and i liked it but switched to castrol tts because it was synthetic.

 

[ellandoh]

drop the needle 1 spot

 

[WillyM]

Just because your bike is stock doesn't mean that it doesn't need jetting changed.
Heat, Humidity,Barometric presure,and altitude effect jetting.

 

[Jaybird]

Willy is right. Jetting needs change with the weather.

I would stick to the 20:1 ratio and jet the bike up to it. The more oil the better in small, high revving motors.

Chasing a spooge problem with the fuel ratio is a mistake. Correct jetting is your only answer. Once you have a good baseline established, you can then tweek ratio to get closer for any given days needs. But you want to fully understand what the jetting thing is all about first.
(when I say tweek ratio, I'm talking about slight changes. Not going from 20:1 to 32:1)

 

[mxmatthew]

change the jetting, leave the oil mixture as it says in the manual; changing the amount of oil is just a "band-aid" fix as i rescently read on this site. If I come across it again I'll post it for you, it's very helpfully if your new to jetting.

 

[CspineRider]

Dont change your oil mixture that drastically, if it calls for 20:1 then use 20:1, jetting comes rich from the manufacture on purpose. If you are riding in hot temperatures right now, then you will have to lean each circuit out alittle, and depending on what kind of riding your doing 1/4 to half throttle than lean your slow jet/pilot jet, 1/2 to full throttle, than lean your main jet alittle. Best thing to do is lean the slow and main 1 number lower from what you have installed now than go from there. Also make adjustments to your air screw alittle at a time to lean or richen. Buy about 3-4 jets of each circuit lean and rich and you will be set to properly fine tune that bike for all conditions.

Here is a link that is very helpful
http://ericgorr.com/techarticles/carbtuning.html