I have a 1991 suzuki lt250r with paulturner pipe & fatboy silencer.I just blew my crank and the guy that fixed it said it might be running to lean, and to check what size the jet is. So I did and my main jet(I think) is 240. Is that the wrong size? P.S its stock bore( if that has anything to do with it) Thanks

 

the jetting is heavily depentent on a number of factors... external: altitude, temperature, humidity.... as well as internal: the pipe & any mod made to the engine (reed block, spark plug, head cc's, compression, K&N filter, porting, spacers, etc.) 2-strokes are very sensitive to all of these factors.

The best way to go is start rich, ride your normal riding area, and do plug checks.... jetting rich will not hurt the engine, but jetting lean can(burns hotter...more oxegen is present, and can burn a hole in the piston, or cause siezure)

jetting 2-strokes is all the same, dirtbikes or quads, the best discussion i've ever seen is on www.dirtrider.net Search the forum archives for jetting in the performance/mods/mechanical section.

 

Sounds like your modded machine is requesting more gas. I'd try a 260 to 270 main jet, they only costa couple of bucks a jet. My girlfriends stocky LT250R is running a 250 main, yours is modded so I'm guessing a 260 to 270 main would be right up your alley.
Take winter into concideration to, you might have to run an even larger main jet. Two stroke, winter not a good combination, it might be smart to go with a 280 and a colder plug for temps below 40 degrees.
GOOD LUCK

2000 SCRAMBLER 400 2X4

SCRAMDADDY400

 

I probly do need a (bigger)main jet, because when I hit powerband and try to stay in power band, it will bogg out. It has been about 50-60 degress f.
I run a B8ES NGK plug.When I take out my plug it has oil on the threads and black stuff on the end of the plug.

 

I have a '90 250 Quadracer that is ported, Boyesen reeds, Paul Turner midrange pipe and Fatboy silencer, and K&N air filter. I run a 240 and ride mainly around 5000'. Runs perfect for me. Like others have said, start rich and lean it out if needed. Also, I believe the recommended plug is a B9EGV. Might want to try switching to that.

 

Ok LT jetting varies each model year, my genuine suzuki lt factory covers em all. 91 stock is 270 up to Frame No 100434, after that 260.

87/88/89/90 main jet = 240
92 = 270

year jet needle needle jet cutaway pilot
87 6FP60-3 Q-8 4.0 37.5
88 6FP63-3 R-0 4.0 30
89 6FP63-3 R-0 4.0 30
90 6FP63-3 R-0 4.0 30
91* 6FP63-3 Q-8 4.0 30
91* 6FP63-3 Q-7 4.0 30
92 6FP63-3 Q-7 4.0 30

* see above for frame numbers for 91 year.

There are quite afew other variable in the engines that effect how they run. The 87 has a totally differnt port layout , head dome shape and reed setup from 88 on. Mufflers changed over the years as did ignition timing and powervalve timing this all effect each model year.

year timing degrees powervalve actuation
rpm 1000 9000 closing rpm opening rpm
87 6 11 5000 5500
88 4 11 5500 6000
89 6 11 5500 6000
90 6 11 5500 6000
91 6 11 6300 6800
92 6 11 6300 6800

On my 92 I had to jet up heaps when I fitted up an FMF muffler and pipe. Removing the airbox lid aids breathing alot on top and leans out even a stocker.

My specs on the stock carb
Main jet #300, then went up to 310 with a mild port job.
needle stock third groove.
Pilot, this went down heaps because it was getting very blubbery if idling for period of time
down to #27.

If you need any other model specific specs drop me a line

Kiwi

 

I have an 89 Lt 250r that has a hot rod & wiseco kit just broke in also has an FMF fatty chamber and silencer and I'm wonder what jet combination will work best. I run my quads hard so I just wanted to get some ideas on jetting so I don't destroy the fresh rebuild this is my first quadracer from the riding I've done so far I like it but I tend to be into the throttle a lot so if I could get a idea of a safe jetting that's not a dog I would be very grateful

 

I am thinking about purchasing a 85 lt250r that needs rebuilt bc it was running lean.idk the jet sizes but i could use some opinions on what would be the best.
The only mod is full fmf system
I live in al and the sea level is 500,temp is around 80.
What would be the best set up do u think for it.
And do u guys know the stock size jets?
And yes i know im really late to the forum.
Thanks,jack

 

Best to start a new thread Jack.

 

^^^^^when you wrote this^^^
do you remember what you went with?? I'm currently having the same situation. Thanks Kyle