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Mikuni Pumper for XR400

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Hi i would like to know on the specific model of the Mikuni Pumper for XR400. I searched for a Mikuni Pumper TM-36 flatside and it returned with a number of options with price range differing from $170-399. And they all states that its 36mm, flatside but does not indicate for which bike. Is there any differences in all the TM-36 carbs?

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Fairly sure it's the TM36-50. Most get them from XR's only because they set them up with the proper cables and machined adapters that fit the intake and airbox boots.

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Fairly sure it's the TM36-50. Most get them from XR's only because they set them up with the proper cables and machined adapters that fit the intake and airbox boots.

And proper jetting, which is huge!

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I didn't want to start a new thread for this, so here comes my question.

I can't start my pumper XR426 with the choke. It will just not even start for a turn. Without the choke, it starts first kick, but it will die quickly (as can be expected) if I don't pull the choke quickly on the already running engine. So when the engine is already running, the choke works fine and the engine runs smoothly with it. But it won't start with it.

I've already tried 15, 17.5 and 20 pilots, no change in the starting. The bike works best with 17.5, with the mixture screw at 3/4 turns out (sealevel, free flowing everything).

Carb is cleaned, engine works great, so it is strange to me...

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Fresh gas and a spark plug change always did the trick on my 400EX. That thing was a PITA to start even with e-start. My XR starts 100x better than that thing did. Same engine so worth a shot. Do you give it a squirt of fuel before kicking?

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Gas is fresh, spark plug changed last year, and it does start running first kick without the choke, so I guess it must be a carb thing. Yes I do squirt a few while kicking a few with the decomp engaged.

Luckily temps are getting up, so it will keep running even without the choke fine.

But still I would love to solve this :thumbsup:

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I've already tried 15, 17.5 and 20 pilots, no change in the starting. The bike works best with 17.5, with the mixture screw at 3/4 turns out (sealevel, free flowing everything).

I'm assuming your pumper is a Mikuni.

3/4 turns out is at the bare minimum fuel screw setting. It suggests that the 17.5 is too rich if the engine runs best with it there.

I know you said you tried a 15, but at what fuel screw setting? At 3/4 turns out, you barely have the taper of the fuel screw tip out of it's bore. On the Mukuni it's safe to run it all the way out to 3 turns out. Opening up the fuel screw more with the 15 is what I'd try.

Also, the starter jet could be partially plugged, need cleaning.

Use this .pdf for tuning your Mikuni. Look at item #73 to find the start jet.

http://www.google.com/url?sa=t&rct=j&q=mikuni%20hs40&source=web&cd=1&ved=0CFgQFjAA&url=http%3A%2F%2Fwww.zodiac.nl%2Finstructions%2F234862.pdf&ei=gqVjT8KHFIKAsgLIkpycCw&usg=AFQjCNGdtlAhAxJ7GtsznzZW1KnjU-MEkQ&cad=rja

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I'm assuming your pumper is a Mikuni.

3/4 turns out is at the bare minimum fuel screw setting.

Yes, it's a TM36. The manual says 1/4 turn is the minimum where a smaller jet should be used. I can set best-idle with the both 15 and 17.5, but with the 17.5 it is definitely waking up better from the bottom, it is more lively. With the 20 the best-idle is with the screw all the way in, and it runs and pulls great.

I've played with pumper timing as well, with the 17.5 I've set to start at around 1/3 throttle.

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