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I have an 86 Honda TRX 250R with some jetting issues. My cylinder is currently being bored, and ported by Forward Motion racing to a 265cc with a mild port job. I am using a Kehin PWK 39mm carb, and I have a K&N intake with no lid, and a full FMF exhaust system. This bike totally failed on me last summer at Sand Lakes OR in the dunes because I think it was way too lean. I took the carb apart yesterday and found the jetting to be a # 172 main, 50 pilot, using the 3rd (middle) needle position. Does this seem lean to anyone else? What would be some good baseline jetting specs to start out with considering the mods?
P.S. I don't know much about this bike because it’s my girlfriends, I have a 04 Z400 that I need to build in order to keep up with her. $$$
Your main probably needs to be in the mid 180's, I run a 180 in a 38AS on my stock bore 88TRX at 800ft elevation with the airbox lid on. I would raise the needle one groove also for starters when you get it running again. You should always start rich on the carb settings and work back so as not to damage the engine. An EGT might be of help, you can monitor the exhaust temp at various throttle settings and know how the carb settings are before engine damage occurs. Keep the temp 1200 or a little less at wot (main jet) and 1050 to 1100 at half throttle (needle)...
Ok, I took the jets of out my 99 CR 250R and they are a 180 main, and a 50 slow, I will try them to see what I get with that setup. I will be running a 92 or 93 pump gas with MC1 mixed 50:1 I think. Raising the needle will also richen the mix up also right? Do I need to run the bike this rich to compensate for the 39mm carb bore? Also how many turns out are you on the screw?
Thank you for the info, I am very new to jetting so I need all the help I can get.
Raising the needle will richen the mid-throttle range (1/4 to 3/4), the pilot will affect idle to 1/4 and the main 3/4 to full throttle. The airscrew is adjusted as needed to fine tune the pilot jet for the highest idle rpm. Start at 2 turns out, if it needs to be more than 3 turns out for best idle go smaller on the pilot and if it needs to be less than 1 turn out to larger on the pilot. The larger carb bore requires larger jets, more air in-more fuel needed also. Be careful on the main, you may still be too small with the 180, check your plug frequently at first, looking for a paper bag brown color down inside the plug. Black is rich, white/gray is lean... Ask your motor builder for suggestions on jetting for your area, they should give you a good place to start....
I am not sure what needle I am useing but its in the middle possition right now, I am going to raise it one and try my 180 main with a 50 pilot. That should give me a pretty rich mix, the cheapest jets I have found at $4 each at www.sudco.com
OK, just for back from a 5 day trip to the dunes and the R did great. What I don't understand is why this bike seems to need so much fuel. I ran a 190 main with a 58 pilot with about 2.5 turns out on the screw/3rd clip position and according to the spark plug, it is rich but it still runs good. I remember this bike have more low end then it seems to have right now and considering its bored to a 265, I think it should.
I have read about ever single 250R jetting post on this site and it seems to me that I either have a really weird bike that needs more fuel, or I need these larger jets because the carb is a 39mm PWK, what do you guys think?
I will check for the Air leak tomorrow. So the pilot sounds high which may be causing the lack of bottom end power, but what about the 190 main? Does this seem to be about right. At full throttle is when this bike REALLY wakes up and starts hauling A_ _.
If you have an air leak the jetting will need go up to compensate for that. I wouldn't worry about the main size as long as it runs good and the plug looks ok. Your probably at or close to sea level which ups the jetting also. I'm running a 180 in a 38AS with a ported stock bore at 800' elevation so you should about right.
The fat pilot will give mushy low end response, drop back one size at a time to see if that helps.....