DRZ400 Stumble/Miss

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8/13/2017 1:14 PM

Hey guys, looking for ideas before I take my bike into the shop and pay $100 an hour to have them figure it out.

Stock Mikuni bsr36 carb
sat for 3 years with old gas, rebuilt carb new seals jets o-rings etc... fires up and idles good... from 1/4 to 1/2 throttle misses and stumbles like crazy while popping.

Had the carb apart 3 times now... main jet is not plugged and needle is brand new. No dirt or obstructions anywhere, clean as a whistle.

Any ideas?

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8/13/2017 6:30 PM

Sounds too lean, hoses connected right? Accelerator pump working correctly? lf everything is set right try lifting the throttle valve needle a clip or two (lower the clip).

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Melbourne, Australia. Current rides: '11 RMZ450, '84 CR500, '06 DRZ400, '79 KX250 with 400 engine, '06 GSXR1000 full Yosh racebike.

8/15/2017 10:21 AM

Go back to the basics if you are 100% sure its clean. Take carb cleaner and spray around your boots to be sure you don't have a air leak. Lower the needle a notch or two just to see.

Also, if the bike came from a drastic different elevation then where your at, there could be a chance it needs a different jet.

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8/15/2017 3:31 PM

Thanks guys but I took it apart again, changed the main and pilot jet again and put in a new spark plug, still no change. I'm thinking bad coil/stator but don't have the tools/knowledge to diagnose. Took it to the shop yesterday.

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8/15/2017 4:49 PM

The throttle range that you quoted is not really related to main or pilot jet. lf you don't have an air leak, adjust the needle, on my wifes DRZ l have gone nearly full rich (clip at bottom groove) on the needle, so that it will accept throttle without hesitation & backfiring.

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Melbourne, Australia. Current rides: '11 RMZ450, '84 CR500, '06 DRZ400, '79 KX250 with 400 engine, '06 GSXR1000 full Yosh racebike.

8/16/2017 8:49 PM

Johnny89superbike wrote:

The throttle range that you quoted is not really related to main or pilot jet. lf you don't have an air leak, adjust the ...more

It has the stock needle in it, no other clips on the needle for adjustment.

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8/17/2017 12:41 AM

Put a 1mm washer under it.

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Melbourne, Australia. Current rides: '11 RMZ450, '84 CR500, '06 DRZ400, '79 KX250 with 400 engine, '06 GSXR1000 full Yosh racebike.