Getting puzzled with my gasser. I run fuel at 85 to 1 50 pilot jet in a Keihin.Air screww set as it should be. Using the BP5ES plug it always fouls at least once an outing. Is it safe to go to a BP4ES if there is such a thing. I'm in a group of five riders and a very smoky sherco does not soot up ever.Any ideas

Plug soot is a symptom, not a problem.

You're asking the equivalent of what kind of pump you should buy for tyres that are always losing air.

Don't blame the plug. The problem is too rich a mixture. Not fuel/oil mixture but fuel/air mixture. Make sure your air filter is clean.

Best is to find someone local who can help you jet it for your elevation and riding. One simple thing you can do without changing jets is to move the clip on the needle up one groove, dropping the needle deeper into the jet. Just be careful to not lose the clip when it comes off. They are tiny and very hard to find.

I am not beta specific on the Kiehin, but I have not needed over a 45-48 range in any that I have run. Yet with all bikes and carbs, I believe it important to "clean them out" periodically with a good hard run through the gears to get some heat into the motor.. You cannot just putt about forever on these things, they will load up with fuel and oil.

Cleanout happens once or twice every ride for me, the bikes are really more high strung than many realize and need a good run.

never mind the smoky sherco, what about the ossa that kicked your a*** !!!!!

OK so I have now dropped the needle one notch. Already after an hour riding it seems so much cleaner but a days riding tomorrow should tell the story.

It sounds like you are on the right track. Keep us posted.

Does it run ok from cold? just a thought it might be a sticking piston ring? Have u tried giving it a proper blast? As that might help clear any foul on the piston and might help clear the exhaust a bit as 2 stroke foul does clog it a bit. I very much doubt it will be jetting unless the jets have been modified lately? As for plug...changing it wont solve it, plus if u wanted to change plug grade i would want to go up rather than down! What oil are you using and mix?

Ye making sure filter is clean can make a lot of difference

I hope that helps a little....keep us posted on outcome

Does your bike rev freely? It does sound like a mixture issue, I have never used the Kiehin carb but is it possible that the choke jet is not shutting off?

If your plug is fouling that much it is probably time for a top end de-coke and clean out, exhaust too.

TLTEL

plug could be it yes ur rite tltel as it could have dirt in it stopping it from turning off, very easy to remove and clean also. As it can be easy to forget to remove and clean it when its carb cleaning time

Update Since lowering the needle I have had two outings and checked the plug once. It seems to have made a big difference and plug colour is nearer what it should be. Pretty happy with it now.. if I do any more fiddling I will post updates. Thanks all