Check this out. I pulled this out after a half hour ride of highway, woods, more highway, then a few laps around the house for good measure just because I love how it runs so good.



It pulls nice up to around 75 or so then when I hold it there it feels like it's starved a little with soft misses. In the woods it's wonderful. Very responsive and plenty of usable power out of the hole. I couldn't ask for more out of a 250 in the woods. Other than that, when I drop the throttle closed it grumbles and pops a little. I'm tempted to call it good. What do you guys think?

Here's what I got. It's an '09 with a KDX snorkel, Uni air filter, FMF Q4 pipe, 13 tooth front sprocket, TM33 pumper carb with 142.5 main, 45 pilot, and mixture screw turned out about 1 turn. And I'm at about 700 feet of elevation, 75 degrees out and humid, and I'm wearing pants.

 

Pants, eh? Well this guy ain't.

Seriously though, plug readings are harder today what with fuel types and such, but that one looks pretty good...no whiteish residue. If it's running lean, it's looks awfully close to right. On that grumbling when closing the throttle, I've had that to some degree on every XR, KLX, and KLR I've owned with aftermarket exhaust, opened intake, and good jetting. I'm thinking it's the nature of the beast.

BTW...that's not me in the kilt...LOL!!

 

Don't waste your time trying to read plugs. Wih todays fuels, and the way single cylinder bikes are, you won't get a reliable reading, and that's even assuming a proper WOT run, and chop, which it sounds like you didn't do. If it were possible to read that plug, it's showing me way rich.

 

Curious...why rich? If you're going by that black in the base ring, I don't think I've ever seen that go away once the plug has been run for awhile in quite a few years now. Like you said, fuel, additives, and engine design have all combined to make street engine plug reading difficult. I agree on the throttle chop and igniton kill to do it right. You almost have to start with a new plug and do a plug test immediately. The base ring on a used plug might clean up a bit after a very long period of WOT, but it would be difficult. It also seems like the ethanol affects the base ring more than the tip or ground strap to produce cooler temps that give the impression of too rich on the base ring. Maybe pure racing fuels are the only way to get an absolute plug reading these days and even then only on a brand new plug...but then that might change the jetting requirements too. I think as long as you know your heat range is correct, you almost have to go by performance through the throttle range to achieve correct jetting. About all you can tell these days from a plug reading on a street vehicle on pump gas are extremely rich...everything on the plug sooted up...and very lean...whiteish almost ash residue built up on the plug. It's a PITA.

 

I still rely on plug readings. Some good thoughts, TNC. Have to look at more than just electrode points. Base ring will tell you if there's any oil being burned-off (assuming the electrode is good color.) I'm not suggesting plugs are the BEST way or ONLY way to "read" your combustion; and I agree, with EFI things have changed, BUT, plugs are one bit of information (at least for me) that is pretty valuable. I grew up with 2 strokes over 40 years ago. I've looked at a lotta plugs. There's a bunch of information (still) if you apply it in the greater context. Good comments^ though.

 

Based on that plug, as long as it's running well, I wouldn't touch it.
All the black on the base, and the tan colour of the porcelain tells me that it's rich. That is, assuming the procedure was done properly. A little rich is not a bad thing. What I found with tuning my race cars, is that if you jetted up to a nice safe, tan porcelain, you were way rich. In my case, about 4 jet sizes. I found it even worse with small 4 stroke bikes. At top RPM, they would flow so much air, and pull so much fuel in, that they'd start breaking up. You'd pull the plug, and it was as white as could be. The plug was being washed by all the excess fuel.

About 20 yrs ago, that same thing happened with a race car that we'd made some changes to. It had me chasing my tail for a week. I kept jetting richer, and it kept getting worse, and the plug kept showing lean

 

But the plug isn't loading up and I'm not sending a little poof of black out the exhaust. Man, it starts nice now. I might change it to a 140 main and 40 pilot when I go out the the black hills in a few weeks because we're going up to 7,000 feet. See, with the 37.5 pilot It wouldn't run at all. Starting it from cold was almost like starting a bone-stock '09 in 35 degree weather. I had to back the mixture screw out 3 and 1.2 turns and I don't like going that far. I couldn't get it to idle until the bike was hot and running at half choke. The pilot jets from Dennis Kirk only come in increments of 5. So I have 40s and 45s.

So you think she's fat? You think dropping the needle will bring it in a little or I should move the jets down one size? I guess I'll know when I go through a tank of gas in 50 miles. I'm really tempted to go down to a 140/40 and see what happens. It's just so much screwing around to take it apart and put it together. I think I'm wearing the clamps out on the intake manifold and air box boot. What do you guys run for jetting in your TM33s?

 

Thats what I would do.

 

I think you're right. Thanks for the input.