any ideas for bad fuel mileage

1999 busa 10k micron race exhaust, pair valve mod, geared down 1 tooth in front, k&n filter dynojet power commander, RC wheels stock width, stock swingarm, new plugs idles and runs fine but mileage is low twenties riding 70 on interstate any ideas? bad tune maybe, elevation about 5000 feet

Mr Bogus

Trouble Makers Inc.
Donating Member
unplug the PC and run it... heck at altitude the thing is already probably a bit on the rich side..


Lily's Daddy
on the back of the air box on the left(as your sitting on it) side is a vacuum hose and sensor..make sure its connected and working, when my hose came off, the bike went rich and mileage skyrocketed down...lifted the tank and there it was little f-n 1/8 inch hose came off the sensor....

Mr Bogus

Trouble Makers Inc.
Donating Member
correct me if I am wrong but unless the thing has a speedo healer, the indicated gas mileage likely will not change (note INDICATED) with gearing change? (the speedo and actual mileage will be off however)
Going from 17/40 gearing (with slips) to 16/42 (with full system) def dropped my mileage, but with good mapping it wasn't THAT bad :laugh: I went from low 40's to mid 30's. You can't blame that big of a decrease on just a -1 front sprocket. You're biggest problem is probably a wayy rich pc map :laugh:


Evil Demon Busa Rider
Donating Member
In order of preference,

+1 on disconnecting the Power Commander.
+1 on checking the vacuum hoses. Also, if they are all connected, make sure they don't have any hairline cracks at the ends where they make connection.
+1 that the sprocket change wouldn't have affected it that much but still worth checking

When was the last time you synched your throttle bodies? Although that shouldn't affect it THAT much.


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