How much does rejetting effect gas mileage, and in what direction?

At first (hmm... thought?) it seems like gas mileage should decrease, since the mix is richer... but if the mix is also more efficient, maybe it increases?  Maybe doesn't have much effect?

At present, I'm thinking of getting larger mains to decrease warmup time on my bike, but I'm also curious what effect (and how much) a full refetting (including exhaust and all) has.

i don't know for sure...

if you rejet then the bike will have more power and run more efficient so if it uses more gas, it wouldn't use a lot more...
but i think the gas milage would stay the same or maybe even increase

I haven't run enough gas through my GS since I rejetted to tell either way.  My return to motorcyling last year was via a 1982 Honda CM250C (picture in your mind a cross between a Rebel and Nighthawk 250).  Anyway, the stock carburetion was pretty dismal.  I switched to a 1983 carb which was identical except for the inclusion of an accelerator pump.  I also shimmed the needle.  My gas mileage went from about 80 before to a consistent 75 after I raised the needle alone.

It stands to reason that if you allow more fuel into the fuel/air mix, that gas mileage is affected negatively.  There is surely a positive offset in improved power, but not enough (I think) to improve gas mileage.  If you rejet, add a K&N and a more efficient pipe, gas mileage really goes down.  There ain't such a thing as a free lunch in this respect.

OK if you really can ride the exact same way before and after the jetting/filter/pipe change then gas mileage will just go down a bit... ~ 5%... You may be able to drop 1-2 teeth on the rear and get taller gearing and reclaim that loss... But you cant turn up the fun meter... Do that and you lose more miles... and gain more smiles.
Cool.
Srinath.

Quote from: richard.... I'm thinking of getting larger mains to decrease warmup time on my bike....

For warmup the best change is the pilot jet and raising the needle.  The larger main has most of its effect at wide open throttle - not really warm-up related.  Post re-jet my cruising highway milage with larger pilots, 150 mains and an exhaust was about the same as stock -  goes down substantially if I am having fun.

I've done a full rejet/pod filter/exhaust/advancer and went down to a 15t front sprocket.

Stock setup i would get a little over 50 mpg.

Today, I topped off the bike with 3.5 gallons of gas and had 170 miles on the counter- about equal to 48 mpg.  But most of these miles were freeway miles.  When I do more city riding or spend more time hitting the throttle, I typically get 42 mpg.  For me there wasn't much of a diff in gas milage- but the difference in performance is staggering...

Like I said, we need to find a time for you to try my bike- you may (or may not) be impressed with difference in tires and jetting (but I bet you will).  And I want to go up against a stock gs to see what kinda of improvement I really got...

What year bike do you ride?

mine is a '96 w/ Katana rear shock, bias-ply tires, 15w progressives on the front.  think that's the only relevent to riding.. would be great to get together, PM me your phone number and I'll call sometime after my demo on monday.

I just got to St. George (260 or so miles) and I had to fill with gas 3 times on the way here.. .not sure why I had such dismal gas mileage getting here.  I didn't have nearly the power I needed, though.. .has made me consider rejetting much more seriously.

Anyway, I'll be on only rarely this weekend, since I'm connected to the internet via cell phone/usb port... 14.4k

Quote from: richardI just got to St. George (260 or so miles) ...I'm connected to the internet via cell phone/usb port... 14.4k

Sheesh - and you say I'm addicted to the board!  :lol: