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Mikuni pumper jetting ?

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So decided the first of many mods for my trusty xr4 should be a mikuni pumper carb

just wondering if anyone can help with what jetting i should use ?

Will be riding between 500ft and about 3000ft .

The bike is pretty much stock except for the baffle being removed from the exaust and snorkel removed from airbox , the carb should be here in a week any help would be greatly appreciated cheers!

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I have about the same set up. 96-97 exhaust end (approx. 35mm opening), UNI filter with snorkel gone and the top of the box cut out bigger. I tried a few different combos and ended up at 15 pilot and 132.5 main. I put the bigger main in because I dual sport a lot and run the roads otherwise the 130 main would be fine for off road only. 

 

Before you install it, get a little gas in the bowl and make sure the pump spray hits the needle.

 

Also make sure the little screw with the spring under it that's on the white plastic arm for the pump is bottomed out. This will make the pump start as late as possible (about 1/4 to 1/3rd throttle).

 

Make sure to tune the fuel screw. Mine seems to be best at 2 to 2.5 turns out from lightly seated.

 

I would say try the standard 15 pilot / 130 main and see how that runs first. When I tried a bigger pilot (17.5) it lost some snap and would blubber with a low RPM load instead of running clean so I dropped back down to the 15.

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I've read of folks running as high as a 22.5 pilot near sea level, which seems insane to me, but it's all about bike set up. I agree with Mich, if you bought from XRs Only it should come with 130/15 jetting. Try it like that first and gage needs from there.

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I ended up at 15/140 at 4300', but mine has a lot of engine work. 

 

+1 on sticking with the 15/130, and tune from there. A 5th gear pull changing from 7/8 to wide open on the butt dyno will tell you if you need to install a larger main. 

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What kind of mileage are you guys getting with the mikuni on an xr4? I got mine from XR's only and have the smallest jet it came with 127 main. Stock motor with a 96 exhaust tip no baffle. Down to 35mpg on mine. Still seems rich.  Dropped the need to the second to the top slot.  Runs good on the desert 2500'. Last time I was on the Kern Plateau it was way to fat. Love the one kick start. It was worth the money just for that!

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My last big ride (200mi), I got 34mpg with 14/45 sprockets. It was about 60% hard pack, 20% highway, 20% sand.

I rode like a normal person for the most part, did about 55mph on the highway, but once I hit the sand I went in to race mode and let it all hang out.

Edited by boogie_4wheel

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I've read of folks running as high as a 22.5 pilot near sea level, which seems insane to me, but it's all about bike set up. I agree with Mich, if you bought from XRs Only it should come with 130/15 jetting. Try it like that first and gage needs from there.

We run 25p jet,still almost to lean.For the other two guys that only get 35mpg.Something bad wrong.That is as bad as our 450s.

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