Carb adjustment hurt fuel economy

[Gary856]

When I got my '01 GS in Jan '09 it stumbled a bit at low throttle opening when cold but ran smoothly when warm, and got around 56 mpg. It took a few minutes to warm up but that was ok. Earlier this year ('10) it started to stumble really badly at low throttle opening even when warm. When I opened the throttle very slowly from idle, the rev would rise and suddenly drop by several hundred rpm, cough and sputter, before catching; it was almost unrideable without slipping the clutch a lot at low speed, even with a warm engine. I had a shop adjusted the pilot circuit (they did some shimming) and now it warms up super quick and low throttle opening drivability is much improved, but the problem is right away the fuel economy dropped to about 45 mpg (from about 56 mpg). The guy at the shop told me that adjusting pilot circuit would hurt mpg overall, but by 10+ mpg? What confuse me is that the bike ran fine for a year when I first got it, so was there a way to fix the low speed stumble without hurting mpg?

In comparison, I get about 50 mpg on my '07 SV650, about 48 mpg on my '03 YZF600R, and I ride them harder than the GS, so getting 45 mpg on the GS is just wrong!     

[romulux]

...a shop adjusted the pilot circuit (they did some shimming)

How does one shim a pilot circuit?  Wouldn't they just replace the jet with a smaller diameter screw?

[Gary856]

I don't know carbs and have only a very vague idea of what was done. I thought they adjusted something (like a screw setting) and remember the word "shim" used, without changing any part. 

[joshr08]

they prolly put a washer on the needle and adjusted the air fuel mixture to richen it up warms up faster and runs better but putting more gas through the carbs.

[black and silver twin]

Adjusting the idle screw would hardly affect MPG considering it only operates at very low rpm/throttle.
Shimming the needle would drop MPG slightly but definately not 10MPG, I have much larger jets 20-62.5-152.5 and 1 washer and full boltons and my mpg only dropped by a few.

[Homer]

The real question is - Is that a Scorpion 700 Neon in your avatar? 

[Gary856]

The real question is - Is that a Scorpion 700 Neon in your avatar? 

No. It's a Shoei RF-1000.