I bought a 1989 LT250R several months ago. When I first got it I was dissapointed with the performance. In a drag race on sand it was a bit slower than my 2003 Z400 and not even close to my Honda 250R. I spent months trying different jetting and pipe/Silencer combinations. Up until last week the best I could do was with the following combination:
FMF Fatty with Turbine CoreII
K&N Air filter with outerware Airbox lid off
270 Main Jet
Needle clip in the Top Notch (Needle as low as possible)
With this combination the LT was about the same as the Z400 but still not close to the Honda(250R). I thought it was odd that the Main jet was large (rich) and the needle needed to be low low(most lean setting). With this in mind I thought that perhaps the needle was worn, so I ordered a new one. When the needle came in, much to my surprise, it was much larger in diameter than the original. I put it in and raised the needle(clip on the third groove). I went for a test ride and WOW!!!! this thing SCREEMS!! now. I'm sure it will beat the Z and suspect it will be as fast or faster than the Honda 250R. Ican't wait for my next Pismo trip too try it out.

I did some research and found that the part number on the original (when I bought it) needle was from a 1987 carb. The moral of this story is to beware when interchanging parts between 1987 and (1988 - 1992) LT's. Some differences are suddle but can have a big impact.

 

How's your TRX set up?

 

Stock Except for Pipe and filter

 

Sounds like a good race LT vs. TRX and a good day of riding.

I put my cousin on my trx for a day while I rode the Zilla. Now he wants to buy it.

 

Is all you did was change the needle? Seems odd since the needle doesnt effect performance at full throttle. also, the carbs from 87 and 89 are the same, arent they?
Anyways, at least its running better.

 

YES!!! Just changing the needle made a HUGE !! difference. Much to my surprise the needles are different 87 vs 89. The part# for a 1989 is "6FP63-3" I suspect this is the part number for 88 - 92. the part number for a 1987 needle is "6FP60-3". The problem before the correct needle was not at full throttle but getting there. Since the needle had to be all the way down(lean) to work at midrange it would not completely clear the jet opening and therfore restrict fuel flow full open. Now with the correct (thicker) needle, the needle is adjusted higher for proper operation at midrange and will clear the jet opening when full open. The difference in the needle diameter is obvious at a quick glance.

 

StangGTmx,
I sent you an email.

 

The 87's had the largest intake ports of any years so it makes sense that they would use different jetting. Congrats!

 

Hey I have a 87 and i just put a fatty on mine, would that 270 jet be the right choice for my bike also or would it not be the same?
THX for ur help

 

It’s not possible to guess what the proper jet should be. It depends upon so many things such as riding type, elevation, temperature etc.. not to mention modifications. I would suggest getting a variety of sizes, there cheep, a couple bucks each. I have from 210 - 300 in increments of 10. There are many resources on the web that describe how to jet. If you ride a 2 stroke, you will need to know how to jet otherwise you risk running to lean and frying your motor or running to rich - sluggish performance, fouling plugs.