my buddy just brought me an 86 lt250r. it has a cool head with 19cc dome, and a kehin pkw carb. he is running 100 octane with booster add . he mixes 100:1 with ams oil synthetic. the carb has a 160 main. the bike runs fine on the lower end and idle when in the power band it breaks up then stall and will not restart untill you put a new plug in. a 160 sounds lean to me but acts like its fowling out. we are at 800 ft above see level. i do not have a lot of experience with these machines. any suggestions. i am not sure if i should start moving the jetting or play with the mixture first.

 

100;1 isnt that a little on the lean side............try 50;1

 

You may need a higher octane fuel to run properly with that dome. I read a website for Coolheads that recommends you run 92 octane with a 22cc dome 100 with a 21 and 109 with a 20. They didn’t even list a 19cc dome.

I just put a slightly shaved 22cc dome in my 91 LT. On 93 octane pump fuel I have the same problem but not as severe. Mine wont stall just breaks up and misfires. I’m going to lean the mixture temporarily by pulling the air box lid and the outerwear off the filter and back the timing off a little and see what happens.

I don’t know anything about octane boosters but I’m always skeptical of fuel additives so I wonder if the booster is really helping or hurting. I would not run less than 50:1 on any oil even if God himself told me I could. I run 20:1 in my 86 and 91 LT. It smokes a bit when cold but is tolerable after it warms up. More lube is always better unless your racing for money and are willing to rebuild more often just for a tiny increase in power or start to foul plugs.

 

tom what is your jetting at? what type of carb are you runing?