250R jetting??'s

[danimal95]

just picked up a DG pipe and silencer yeah i know they are cheap but i got a really sweet price,what main a pilot jets do i want to start with?the bike is stock except for the exhaust and a k&n replacement filter.i am at about 800ft above sea level.thanks

[Mosh]

If your bike runs good now,with the stock pipe and jets,or even a little rich,which stock 85 250r's were from the factory,I would bolt it on and do a plug chop.See how she runs.


Other than a little weight saving and bottom end pull,the Dg is not far from stock.
So the jetting should be fairly close.

[TeamGeek6]

1.) Pipes dont control jetting, famous old wives tale. Theres an indirect effect that goes on in the cylinder. Jetting controls the amount of fuel that goes in the carb based on how much air goes through the carb, and not the exhaust system. If the plug appears to change colors because of exhaust changes, its due to things that happen in the cylinder, not the carb. The carb is stupid, it only knows to follow airflow. If the exhaust system is loosened up a little and allows more airflow, the carb automatically makes up for it- thats its job.

2.) That stock carb was (is) a LOT rich because Keihin screwed up the floats, look at sudco.com on the PJ drawings and compare the float in the picture to the one in the carb. On the 86, they molded the float upside down and makes it run super rich. Ive torn the 85 PJ apart and the float is the same. Fix that and it runs fantastic. I did, and the spark plug comes out clean and engine runs much cooler.

3.) There is no such thing as asking what jet to throw in, every engine is different, look at spark plug colors. When in doubt, start with stock jetting.

4.) Nothing wrong with a DG pipe. May not be for all out racing, but not many of us do that.

[Jason Hall]

I have to disagree that jetting won't change with a pipe on a 2 stroke. A different shaped pipe will draw air through the cylinder differently. I took my 310 Pro-x engine out of my quad with a old FMF Inframe pipe. I put the engine In my atc with all the same parts, except a FTZ drag pipe. I had to re jet completely. I went from a 178 main with the TRX and fmf, to a 165 main In the atc with the drag pipe.

[Liquid-Darkness]

I find that the powerband on a two stroke kicks in alot sooner and has a shorter burst of energy with leaner jetting. With richer jetting, I think a two strokes powerband hits a little harder and makes the power range wider. I also feel that too rich of jetting can make a bikes powerband sometimes not kick in quick enuf and or not rev into the powerband making any usefull power impossible to use in harry thick dirt situations. Too lean of jetting can fry a topend.

I just jet to each mod like this: Start with a few sizes above stock and never jet leaner then two sizes above stock jetting. Up or lower your main jet so you can ride the pipe through soft clumpy dirt, but still stab the throttle from a clutch engaged rolling start and hit wot with very little hesitation. Works for me and my two stroke is still rollin. Good luck.

[danimal95]

1.) Pipes dont control jetting, famous old wives tale. Theres an indirect effect that goes on in the cylinder. Jetting controls the amount of fuel that goes in the carb based on how much air goes through the carb, and not the exhaust system. If the plug appears to change colors because of exhaust changes, its due to things that happen in the cylinder, not the carb. The carb is stupid, it only knows to follow airflow. If the exhaust system is loosened up a little and allows more airflow, the carb automatically makes up for it- thats its job.

2.) That stock carb was (is) a LOT rich because Keihin screwed up the floats, look at sudco.com on the PJ drawings and compare the float in the picture to the one in the carb. On the 86, they molded the float upside down and makes it run super rich. Ive torn the 85 PJ apart and the float is the same. Fix that and it runs fantastic. I did, and the spark plug comes out clean and engine runs much cooler.

3.) There is no such thing as asking what jet to throw in, every engine is different, look at spark plug colors. When in doubt, start with stock jetting.

4.) Nothing wrong with a DG pipe. May not be for all out racing, but not many of us do that.


i understand how and why a carb works,however more air in = more air out and vice versa,and generally speaking when you free up some flow you need to compensate with more fuel,more essential on a 2 stroke of corse.

i wasnt asking which jets to "throw in"i was simply asking what a good starting point would be.

and i have had several different pipes on my banshee form FMF to the pro curcuits that are on it now and i liked them all,i said cheap pipes due to the fact that alot of threads on this board seem to dislike the cheaper pipes,but like i said i couldnt pass up the deal

[danimal95]

I find that the powerband on a two stroke kicks in alot sooner and has a shorter burst of energy with leaner jetting. With richer jetting, I think a two strokes powerband hits a little harder and makes the power range wider. I also feel that too rich of jetting can make a bikes powerband sometimes not kick in quick enuf and or not rev into the powerband making any usefull power impossible to use in harry thick dirt situations. Too lean of jetting can fry a topend.

I just jet to each mod like this: Start with a few sizes above stock and never jet leaner then two sizes above stock jetting. Up or lower your main jet so you can ride the pipe through soft clumpy dirt, but still stab the throttle from a clutch engaged rolling start and hit wot with very little hesitation. Works for me and my two stroke is still rollin. Good luck.


thanks thats pretty much what i was thinking but i havent tuned a 250R in at least 10 years:eek: