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TMX Mikuni Carb jetting?

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Hello all, I have a 2002 CR250 with the TMX Mikuni carb. From what I have read about them is their any point trying to get it jetted properly or should I just go straight for the PWK?

The setup on it at the moment is all standard.

Thanks in advance.

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I have an '02 and an '03 and fiddled with the TMX on both of them far longer than I should have. Buy an Air Striker now is my recommendation.

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Have both. Mikuni can be a great carb, but still seems to be more sensitive to temperature changes. Also the oring on the valve seats need replaced every now and then. the JD kitted mikuni is a great option. But you will likely still be swapping brass more often than a pwk owner.

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Which bikes use the PWK airstriker? so I can look for a used one first. Thanks for the input so far.

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you dont need an airstriker. jetting is ez. just look at the chart for a starting point and make slight adjustments. for instance with my setup i use a leaner jet needle and one size smaller than the chart recommends. i am still using the same pilot jet as the chart but next full rebuild i will be switching to one size smaller (just to see if it makes a difference). i also am mixing at 40:1. may not be significant but i dont foul plugs ever and ive never burnt a hole in a piston. im not saying the mikuni is ez to get right but i am saying its possible and ive been doing it consistently for the last 4 years.

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I'm not convinced all the TMX problems can be solved by swapping jets. I'm very new to the game, but nothing I did helped my 03 250. The major issue for me is that you can get the bike to idle, or you can get the bike to run decent down low, but never both. Something to do with the idle circuit I suppose, but I have to open up my throttle slide substantially to keep the bike from dying on idle. This kills the low end, and I've tried a few richer pilot jets.

And yes, that locknut on the idle screw is a pain.

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I think you'll find that if you want your TMX to jet well, you'll need set the carb up with no idle.

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I think you'll find that if you want your TMX to jet well, you'll need set the carb up with no idle.

That's kind of what I believe. Maybe for a pure race bike that is fine, but for someone like me who is just casually riding around, it's unacceptable. But I'm still going to try and work it out before I throw a PWK on.

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Good luck. I messed around with those damned TMX carbs using OEM jets and needles and JD Jetting kits until I just couldn't stand it any longer. I could get the TMX running very good only to have the jetting go south because of a minor weather change. Screw that! I don't want to have to mess with the carb every other day. The Air Strikers have been a lot more consistent.

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Good luck. I messed around with those damned TMX carbs using OEM jets and needles and JD Jetting kits until I just couldn't stand it any longer. I could get the TMX running very good only to have the jetting go south because of a minor weather change. Screw that! I don't want to have to mess with the carb every other day. The Air Strikers have been a lot more consistent.

Were you able to get it to idle? For me, I don't think I'd need the jetting to be absolutely perfect, but I'd like some consistency. PWK becomes more tempting the more I think about it.

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Were you able to get it to idle? For me, I don't think I'd need the jetting to be absolutely perfect, but I'd like some consistency. PWK becomes more tempting the more I think about it.

No, I never did get them to idle right.

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IMO, JD does nothing for the TMX. The real test comes this summer for me. If it carburetes cleanly at high elevation and high temp then it's a keeper. So far it's clean when low and "cold" out.

You're the only person I've seen post that he had trouble with the JD kits. You must have got a lemon. I liked the kits I bought.

When the TMX is right, it rips. I just couldn't keep the TMX carbs dialed in like I have been able to with the Air Strikers. I don't have much elevation changes down here so that was one problem I didn't have to deal with. Temperature is another story and was a big problem.

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The bike everyone supposedly loves, the 2001 CR250 came with a Mikuni TMX11A but a different TMX11A then what we use on the 05-07 CR250. I wonder why I don't see complaints from people who had that CR250. Maybe the case reed engine is making it hard to jet, I know people claim to have no issues with the Keihin PWK. This mikuni looks like any other carb, I can't tell a difference anywhere on it, that would make it more touchy than any other carb. This doesn't make any sense at all.

I bet the Mikuni problems are all coming directly from the float level.

And why is everyone going with a PWK, Interesting fact: the Keihin PJ series is their most trustworthy and reliable carb for a two-stroke.

And why not advocate giving this carb a try http://www.mxsouth.com/keihin/keihin-complete-carburators-pwm-carburetor.htm as opposed to the PWK ?

Edited by Atieri

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I think you'll find that if you want your TMX to jet well, you'll need set the carb up with no idle.

I watched a race that was posted on this message board the other day, it was in 2003 and RC won an out doors race on an 03 cr250. One thing I noticed at the end of the race was he stopped next to his mechanic and you could hear his 250 idling like a 4 stroke, they left it that way for about 30 seconds and it just purred away. I don't buy the idea that you have to jet a bike to not idle to make it run right. I don't know what RC's setup was but it obviously would idle.

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Well you can't have the pilot rich, even sitting at the starting gate blipping the throttle you will still load up and never have a chance of getting the holeshot. I really think the float level is the problem on the Mikuni carbs, I was told to try 8.5mm from the default 7.5mm float level, which would shut the gas off earlier and would then require more vacuum from the engine to pull in fuel. I heard they just suck too much fuel at the factory set levels. Also with the default float levels there is not enough air in the bowl for atmospheric pressure to be able to do it's thing, I bet thats all it is, instead of messing with jets, why not try different float height settings.

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It could be a float level thing. I'm not sure about the lack of air in the float bowl being an issue, pressure is pressure and when we're talking about a low density fluid such as air, small height differences don't mean much when it comes to static pressure.

If your having to really screw in the idle adjustment to keep the bike from dying, that would mean you will require more fuel for your idle circuit to compensate for the additional air, correct? You're allowing more air to enter the engine, and furthermore your providing less vacuum to pull fuel in through the slow jet. So I kept going bigger and bigger on the pilot jet, but the only way the bike would run half decent at small throttle openings was if I kept the idle adjustment screw well out. Maybe I should increase the amount of fuel in the float bowl?

Carb jetting is an interesting topic...

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If the carb is that sensitive to temp and elevation changes, it's in the bowl where the problem is. It's not the air flowing through the barrel that's doing this.

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i use a tmx, bike rips, idles and only has the slightest drip after a full desert tank. its not that hard to jet. if yall dont want your tmx carbs send em to me ill use em.

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