I have a 1989 Suzuki LT250R that I recently (well, about 2 years ago, but I've only ridden it for about 2 hours) had rebuilt. At the time I went from the stock exhaust to the Paul Turner High Rev pipe and Fat Boy silencer. I believe it also has Boyesen reeds although I'm not positive on that and I'm running a NGK B9 plug. Although I've run a B8 as well and have both. At the time of the rebuilt I asked the guy the re-jet it for the pipe. However, I'm pretty sure that he didn't touch the carburetor. The first time I rode it after the rebuild it fouled a plug after about an hour of riding making me think it was running rich. It also blows oil out of where the exhaust pipe connects to the cylinder also making me think it's running rich. I'm running the gas/oil at 32:1 (the same as my CR500, so I can use the gas in both) and I'm riding it at approximately 1325' above sea level. Honestly, this thing runs like a bat out of hell though. It doesn't bog or have any symptoms I've seen in the past of improper jetting.

Well, after letting the atv sit for the past year I had some trouble getting it started. This made me pull the carburetor apart and clean it. While apart I looked at the jets and saw that the main jet was stamped with a 200, the pilot jet was stamped with a 25, and the needle was stamped 6cp63 with the clip on the 3rd slot down. These jets seem way smaller than what I'm seeing most people online run. I know the elevation, plug, etc. all have a big part in jetting, but I'm seeing most guys running 260-270 main jets and quite a bit larger pilot jets as well. That makes me wonder if I'm running way lean. What signs do I need to look for to see if it's running lean? I hate to change it since it does run so well, but I don't want to be redoing this motor anytime soon either. Does this sound like I'm likely running lean? Any idea on where I need to start with the jets? What signs should I look for?

 

You have to be careful with jetting sizes. Not all manufactures number their jets the same. On my ATC250R, I run a 142 main at 4500 ft with a premix ratio of 40:1. My OEM jets are Keihin. A look at your spark plug will tell you if you are rich or lean. If it is dark and oily, you are rich. You will not foul a plug if you are running lean. You seldom have to mess with the pilot jet since it has to do with idle to approximately 1/8 to 1/4 throttle. The main jet affects performance from 3/4 to full throttle. A service manual for you machine should give you a base line based on your altitude. Keep in mind that your premix ratio also affects jetting. Stay away from jet kit and just order some OEM jets. Get yourself a few extras and dial it in. The stock jet size is a good place to start. Keep it a hair on the rich side.