hi, help with lt250r pilot and main jet

[Joelt250r]

hi, i just got my lt250r together and now i just have to tune it. Problem is, is the carbs pretty big like a 38mm mikuni flatslide carb barely fits in the intake boot. also, it has boysen power reeds, an is bored 80 over. 87 cylinder with the larger intake port. it has a 290 mainjet in it right now, i'm not sure about the pilot. I've noticed some people running mainjets close to 400 in mikuni carbs , and i have a new piston i'm worried i'm a little to lean to break it in right. So i was wondering if any of you has every had a lt250r 80 over minor mods, just to get me in the ballpark to start tuning i was thinking maybe a 380 mainjet i'm not sure about the pilot though. it idles for like 20 seconds then dies i think its staving.

[nnnon632]

what kind of carb is it exactly. your probably going to need a reed spacer or a zilla boot. and you should run high speed tests on the bike. find a stretch or land where you can bring it through all the gears and kill it after topping it out for a few seconds. check the spark plug and work from there. because unless we have more details man, we cant do anything

[Joelt250r]

ok i figured out what kind of carb it is, Mikuni TMX Series 38 MM Radial Flat Slide. heres a link to where i found it http://images.google.com/imgres?imgu...26tbs%3Disch:1

[Morph0906]

a plug chop and a pic of the plug is really what we need!!! welcome to the site!!

[rb0804]

Originally Posted by Joelt250r

hi, i just got my lt250r together and now i just have to tune it. Problem is, is the carbs pretty big like a 38mm mikuni flatslide carb barely fits in the intake boot. also, it has boysen power reeds, an is bored 80 over. 87 cylinder with the larger intake port. it has a 290 mainjet in it right now, i'm not sure about the pilot. I've noticed some people running mainjets close to 400 in mikuni carbs , and i have a new piston i'm worried i'm a little to lean to break it in right. So i was wondering if any of you has every had a lt250r 80 over minor mods, just to get me in the ballpark to start tuning i was thinking maybe a 380 mainjet i'm not sure about the pilot though. it idles for like 20 seconds then dies i think its staving.

What pipe are you running and where did you get the carb? Buy it new and tell them it was for a single 250? The reason I ask is that they are able to change the jetting before the carb leaves the factory. I have never played with TMX's on the LT's but I can tell you that with the standard flat slide 38 TM and an FMF pipe, midly ported, that a 300 main jet is a ball park number. With that being said, you would have to tune from there and that air through the carb is going to be a bit different then that of a regular flatslide. How this is going to affect your jetting, I can't tell you. I use a comany by the name of Fox Distributing for my Mikuni needs. You should give him a call. He is into Snomo's so he may not be able to give you exact specs but will be able to tell you the difference between the TM and the TMX jet wise and get you pointed in the direction so that you don't seize your engine first time out.

[lumpy300]

i had a tm38 on mine and was running a 330 main jet. and it was a 89 so your 87 will need a lil more fuel due to the intake and bigger bore. i can't remember what pilot jet i had, but if it will idle and then just fall off and die, your probably rich on the idle circuit. if it was lean it would want to idle up instead of down.

[rb0804]

Did you play around with the idle screw at all, or do you know where it is set at now? The 87's have less port timing and a larger intake runner. Unless it has been seriously ported with the transfers and the exhaust raised, I seriously doubt it will require a larger main jet.

[Joelt250r]

yea i'm running fmf fatty pipe i had a chance to run her around some today, my quads at my grandparents farm. but , yeah i had the 300 main and ran it,i kept checking it and it has to be a little lean. the plug was barely turning any color, i was thinking of a 340 size and now i really am since u had a 330 on an 88.

[Joelt250r]

it idles with the slide idle screw with the sping on it not even touching the slide. so the slides the whole way down. at 2 turn out to 1 1/2 turns out it will idle so i'm thinking its ok , but should it idle with the slide all the way down?

[Joelt250r]

yeah i probably won't mess with for about a week or so