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2007 Suzuki DRZ400s sudden bad gas mileage

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after lots of searching and due diligence i need someone to narrow this problem down for me. a mystery is i'm suddenly getting 36 mpg on my little Suzy :confused: , down from an averge 57.5 mpg. 55-60 mpg was a constant a month ago, that i could swear by when anticipating the next fill up. wether i was ridding hard in the santa cruz mountains or riding melow on errands. now, no matter what the condition or driving habit i get 36 mpg. the crazy part is there is no driveability issue with her :excuseme: . a bit of sloppy stock suspension for my ass butt i'm moments away from suspension upgrades. :blah:  maybe an fcr39 mx carb...mmm supermotard wheel set :wub:.


-one intermittent pre-existing issue that's always been present since i bought it at 7000 miles is the bike just dies when the idle is slightly cracked, usually when i'm about to take off at a light. :lame:

-no new power mods were added recently.

-no extra/lack of power, no backfiring/starting issues, no gas fumes/leaks.

-the spark plug looked tanish brown, replaced it anyway.

-the oil was changed with lucas 10w40 synthetic and doesn't smell like gas (level looks a little higher than when i filled her up 400 miles ago).

-took apart the Mikuni carb with stock jets and cleaned everything i could take apart (it looked brand new inside no diaphrams were cracked).

-checked the vacuum powered petcock, no leaks when "on" with vacuum and gas lines are disconnected.

-checked the cam timing and valves, one exhaust valve was out of spec @ 1.8mm instead of between 2-3mm (still not the suspect).

-cleaned air filter and housing. inspected, lubricated, and adjusted rattely chain. adjusted tire psi's.

-replaced the front fork oil cause it was due. both wheels spin freely from brake caliper misalignment.

-also i'm great at math!


after all the work performed, Suzy felt more responsive than she ever has felt. but i'm still getting 36mpg on a gentle ride.  

anyways my question is should i just upgrade the carb to the klein fcr39mx to remedy my problems or is there a way to identify and fix the problem? could it be a throttle position sensor issue or leaky accumulator pump diaphram? or is their a gremlin in my tank that sips gas when i'm not looking?


bike mods/stats:

-99% ridden on road 1% dirt

-9000 miles on odometer

-dessert tank 4.25 gallon

-80/20 dirt tire on front, street tire on rear

-3x3 air box mod

-supertrap muffler tip

-reupholstered softer seat

-subtracted charcoal canister

-all black plastic

-and i'm dead sexy at 230lbs out of the shower :banana:


thanks friends



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yhgeorge do you speak for everybody at this forum?


good to know. more mysteries are all i see on my horizon with your help. you could have said where to go instead of wasting both of our time. obviously i should delete this thread and start somewhere new. but i can't figure that out. thanks for more problems.....or you could be a real man and accept my challenging question and help out. if i walked into a shoe store and a man asked me about what supplements to take with a sprained ankle i would never say "wrong store", i would help him figure out his issues. thumper talk is just that and the people should never be too pretentious or compartmentalized to deny helping fellow riders. but don't worry about me i've been knocking on other peoples doors about this issue, before you thouorghly explained to me where i was. 

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