I have an 88 LT 250 R that i have done some things to but i cant seem to get the jetting were it needs to be, i have an 80 over piston (68 mm) wiesco , boyesen power reeds, cylinder is ported and polished, head is shaved .010, 12/41 gearing, race clutch, billet basket, fmf fatty pipe and power core silencer, i run klotz at 32 to 1 ratio, i have the jetting at 40 pilot and 240 main, seems rich on the big end, and i also have the air screw 3 turns out, if i change any thing like go up one pilot jet so i can screw the mix screw in some so it dont fall out, or jet down on the main it will not run for crap. can some fello R riders tell me where they are on jetting and with what mods? thanks all very much...Eric

 

Jetting is so specific to your machine and location that somebody else's numbers will probably do more harm than good. Read this and just go step by step. Also, the stock mikuni carbs tend to have problems with the needle jet wearing and causing the low end to run way rich.

 

I feel your pain. I spent a long time trying to get my bike to run right. Played with jets, mains, pilots and clip position. I thought I was really close but never got it right. I end up taking it to Trinity Racing and had the pros put it on the Dyno and set the bike up to run at its best. I am extreamly please now.
This is very specific to every bike so its hard to suggest ideas when every little factor is important. You can take a look at my profile and see the Dyno reports. Im running a 25 pilot 240 main 3rd position on the neddle.

Good Luck

 

240 is stock size and is going to be way lean with aftarmarket pipes and aftermarket reeds.I would think the only reason you would have the air screw out 3 turns is because of the huge pilot jet. i would start with about a 270 mainjet and maybe 1 size over stock pilot to start with.im pretty sure stock pilot is like 35. Does your 88 piston have the "u" shape cut out on the intake side of it?

 

the directions with all my aftermarket parts said i would have to lean it out not fattin it up, with the aftermarket parts, besides if i jet it any higher it wont run for crap and is real hard to start. and yes it has the u shape

 

70 percent of my hard to start jetting was too small of pilot. and i never put after market parts on and had to leaner out. id be careful

 

are you using stock 34mm carb? If so not gonna work well with your curr setup. you need at least 36mm to 39mm I am running close to what you mention and Have 39mm Kehin airstryker. I also have no airbox I use K&N clamp on
my 02 cents
k-dog

 

Bigger carb will definately help you out.You will notice the difference.Later