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 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.

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.