250-500cc 09 WR 250 TMX Carb - Making it Work

I am trying to get the TMX carb jetted correctly and I'm really close except for finding the main. Maybe someone here can help.

Here are my current settings:
Elev. 6000 ft
Temp. 70 deg. (all of my jetting tests have been near the same temp)
Pilot 30 (AS 1 1/2 turns out)
Needle GAY needle (3rd clip)
Main 430 (have tried 390 to 450)

I have it running very well up to about 3/4 throttle. With all of the mains I've tried, the result is always the same. When I take it through the gears and hold it wide open on a dirt road, above 3/4 throttle, the power falls flat and it doesn't scream on top like it should. I'm not a jetting expert but to me it feels like it's a lean condition. And the plug is dry and light gray also looking lean. At my elevation, going to higher than a 450 doesn't seem right since the stock main was a 460. And the last time I tried it, I was wide open and reached down and pulled the choke and it didn't change anything. When trail riding I'm rarely wide open and I don't even notice that the main isn't right. It has good power off the bottom and throughout the range when riding. I can ride all day and get very little spooge on the silencer, but when I do my wide open runs to check the main, the pipe gets wet with oil running down it. I was thinking that this indicated that it was rich at wide open but that's not consistent with the plug reading. So could this be just residual oil coming out of the exhaust?

I was told to try a plug without a resistor - B8ES instead of BR8ES and it still does the same thing.

I have checked and adjusted the floats.

I have not checked the power valve. I can feel when it opens when riding and there is a delay in closing when the rpm's go down. Is this normal or could there be a problem there?

Is it possible that even at 6000 ft I may need to go higher than stock on the main jet? The service manual chart recommends 390Main/35Pilot at 5000ft/50degrees. The 35 Pilot was rich.

I've been very methodical about only changing one thing at a time and I'm not sure what to do next from here. Check PV? Keep trying richer mains? Something else? I'm really close so not giving up on the TMX yet.

Hello! To me it sounds like rich on the needle and lean on the mainjet. I think the jetting is almost identical with the 300 that i have, and my bike is too rich with that needle in the Mikuni. I used the 6DEY15-74 needle with good results in 2nd slot from top in the winter. It was good, but not close to the Keihin PWK. I had 470-480 main in the winter at 5-10 degrees minus, and a 40 pilot with this needle. I live at sealevel btw.

Johnny

My 2 cents worth
surely its the main that the issue if affecting WFO (or electrical)
it sound like its rich if putting choke on doesnt change anything
try it on a cooler day or early morning to see if it improves
try it with 390 main again

I was thinking the same thing, but what doesn't make sense is the plug readings...they definitely looked lean to me. And it didn't blubber at all or smoke alot like 2-strokes usually do when rich.

Johnnymannen,
If the needle was rich I would expect to see it somewhere besides full throttle. Right now it is good everywhere else. The stock needle had similar dimensions as the GAY needle but at the end it quickly tapers to a straight section at the end. My understanding is that the GAY needle is actually leaner than the stock needle. The GAY needle was lean in the 2nd clip but seems very good in the 3rd. Maybe the 250 needs a richer needle.

My mikuni TMX was always really strong up top with a 380 main now I run a 175 main on a PWK which is similar to what other 250 /300s are running
because you are at such a high altitude I think you should try the leaner main with a new plug and do a plug chop refer PV Dukes recent post in recent WR 125 problem thread
use the original needle at middle setting - keep testing
Maybe Dtyppt can help more as he has a wr250

Read the jetting section in this link(hope the link works) it's old but still applies. http://www.datafan.com/TunersHandbook/2-strokefiltered.html

http://www.datafan.com/TunersHandbook/2-strokefiltered.html

Sorry for posting it twice. I did not think it worked. Read and do what this guy says to do with first testing the main jet and needle. It also sound like the power valve is gummmy?

Well, my bike ran smoother with the DEY needle compared to the GAY as it´s not so rich at light throttleopenings as the GAY, but it´s richer in the middle and on WOT. The idle and light throttle gave me a lot of spooge with GAY needle.

Johnny

STOP ! you are LEAN on the main!!! go up two sizes now...see steps below.

and, again, if you are looking at the tailpipe to confirm your jetting guys, that's the wrong end!
look- some bikes spooge, some dont. it's a matter of fact and a lot of things...mostly the packing gets saturated in a hurry. honda-brite the mess after a ride and forget about it. will an overly fat bike spooge more than a really lean one? you bet!

here's how mine looks after tight stuff and WFO stuff...(see pic) soimetimes there more, or less. sometimes it dripps on the master from the union and the caliper gets some too, my pants too if i'm floundering...the stuff gets everywhere, who cares!

please read the plug.

warm up the bike and clean it out. install a new plug. do a 3rd gear WOT pass, hit the kill switch, chop the gas and pull in the clutch all at the same time- DONT LET IT IDLE!!!. pull the plug and read it. dark brown? yer safe for now and can continue your verification & other circuit tuning. start rich. go lean in baby steps. one step at a time!

http://www.cafehusky.com/forums/showthread.php?t=8039

lemme know if ya got any ?

Since the 450 had the same result, I'm guessing that the 460 won't be that much different and I may need to go higher. I'll try it again this weekend with the 460 Main. This is 5 steps richer than the manual recommendations for my elevation.

the plug will tell you which way to go.

read the plug, luke....reeeead the plug.

I measured the needles at approximate quarter points for comparison. The stock needle (6BFY43-74) in the 2nd clip is richer (thinner) than the 6GAY69-74 in the 3rd clip, everywhere except at the center section where the BFY is slightly thicker. Since the BFY is thinner on the lower end, it should be richer over 3/4 throttle, right? So I tried it with the 460 main this evening and the result is still the same...power just stops increasing at 3/4 throttle and plug is light gray. It's like it reaches peak power and when I twist the throttle the rest of the way, nothing changes. No surging, pinging, blubbering or anything - it just levels off. I'll try and find a 480 main to try, but it's confusing to me when the manual says 390. Am I missing something?

And I did check the float level again. When the needle valve closes as you tilt the carb, the float seam is parallel to the side edge of the carb, similar to the way my KTM manual describes for the Keihin. Is this correct?

Read the plug and give it what it wants before you melt the top end. It doesn't matter what other people run for jets it only matter what is working for your bike.

+1 lanky.

dood- put the calipers away. slow down. if it's lean, richen it up. as i've said, the OM will get you in the balllpark for heat cycles etc but....grain of salt there. one thing atta time.

stop playing with other circuits when we are working on the MAIN. you have to get the main close or right FIRST.

do you have an air leak somewhere? let it idle and warm up then short spurt spray WD40 around the boots, etc, see if the idle goes UP.
if you have a mechanical defect somewhere you can jet it all you want and not get any results. make sure your bike is good to go, 110% mechanically perfect.

if your midrange and off-idle are good i doubt there's an issue with your machine. other than jetting.


as i've said before. go up 2 sizes atta time, start RICH.
if you keep testing it lean and yer gonna burn it up!!!

read my post on "jetting your two-stroke". fatten it up till it fouls a plug then go down one step. leave the needles, PJ etc alone. fatten her up till she blubbers and needs a good clean out then let me know how it looks.

http://www.cafehusky.com/forums/showthread.php?t=14651

My intent was simply to make it as rich as possible at the top end, so I put in the richer needle and 3 sizes up on the main. I do know better than to screw with other circuits. I was just trying to get it to blubber.

I went down last night and looked at the boot connection at the reed cage and I think I might have a leak there. It had a slight film of oil around it that was just enough for dust to stick to it. What is the best way to seal it? Can I just use some Silicone RTV stuff or do I need to make a gasket?

please give your undivided attn to the main and getting it to turn the plug dark brown.

start the bike and let it idle. then, when its warm and idling, give that area a spritz of WD40 or some such. if the idle goes up you have a leak. then, make a gasket. if either of your crank seals are leaking it's usually pretty obvious and hard to start.
never use slilcone on an engine or any part that is around or near gasoline as fuel and it's vapors turns it to jelly and there's no way to get those little dingle-balls that squeeze out on the inside cleaned up then they break off and go into wherever. silicone is for fishtanks. yes, please make a gasket.

FWIW my powervalve wasn't opening and acted exactly as you describe, just fell off the top end

My power valve from the factory was not adjusted correctly or had moved. I had a flat spot on top end. Someone on here recommended going back and checking it and that was all it was.

Hang in there! You'll get it!

Darin

I checked the power valve and the nut holding the plate with the tab on it (for limiting the opening) was loose. I could see when looking in the exhaust that they were able to open too far, where they appeared to be actually reducing the flow. I adjusted it so when the valves were open, they were flush with the bottom of the exhaust port. Somebody please let me know if this isn't correct.

I also sprayed some WD40 on and around the boot and could not see or hear any indication of an air leak. So I tried it again on the trail this weekend before changing anything else with the jetting. It was very inconsistent. As times the idle would be higher than others. At times it ran well and at other times it was way rich. I even got it to foul a plug when I really revved it at 8500 ft. It always had clean, strong low end though (and I had the 35 pilot in). Unfortunately, one of the radiators developed a leak and now I need to send it out to get repaired. There was no impact and it's not dented or bent - just started leaking.

The radiator is going out today. Convinced that I have and air leak, last night I pulled the carb boot and put a gasket in and sealed it. It definitely wasn't sealed. There was premix on the surfaces that should have been sealed and dry. Hope that takes care of it.

I only have 30 hours on this bike and I am not an abusive rider. Air leak, loose power valve adjusting nut, and now a leaking radiator...I have been trying very hard to like this bike, but this is getting ridiculous.