i just bought a 2002 c10 and have had a 1986 for several years my 2002 gas milage is varing a lot a friend and i rode 280 miles i filled up 3 times during the trip depending on how hard we were on it i got at best 48mpg and at worst 40 then at home i was pretty much babying it and thought i should have got at least 45mpg or so and only got 35 is it possable my carbs need adjusted?

Your math doesn't add up.
I can almost always go 250 miles before I hit reserve. You went 281 and filled up three times?

Or..... If you are doing partial fill-ups with only a small amount of fuel each time, it is pretty hard to fill back up to the exact spot each time giving you skewed results.

I usually go about 200 around town before filling up.  On the highway, I go to about 240.  I get about 35 (or worse) just commuting back and forth to work for tem miles in city/residential traffic - just don't care about getting good mileage so I twist the wrist when I care to.  On the other hand, I get about 42 to 43 on the highway most of the time (running 80+ mph).  Ironically, when the wife has been on the back, i've gotten as good as 46mpg because i'm really babying the throttle and not trying to burn the tire off.

Sounds like your carbs are OK, you just need to burn a tank out before you fill up. You also may want to check the float levels to make sure they are not too high which can give bad gas mileage.  It should be at the bowl parting line and all be equal.

Typically I get 41-44 normal driving. Got my best of 50+ on the BRP in 3rd and 4th...go figure.

Or..... If you are doing partial fill-ups with only a small amount of fuel each time, it is pretty hard to fill back up to the exact spot each time giving you skewed results.

+1  Your calculations will be more correct if you run through more of your tank between fill-ups.

I vary between 36 and 42 depending on how hard I am riding.  Though sometimes the bike surprises me.  Recently, on one tank, which included ~25 miles of time on a race track, I got 43mpg. 

If I try to get good gas mileage I can hit 48.8 mpg. Mostly I get 44mpg even on the highway.
If I run full WOT  I get exactly 20mpg. This is with a well tuned well maintained bike with carbs meticulously  maintained.

I get 42 -44 pretty well split between highway and city on commute between 30 and 65 mph.  Oddly, I get 48 through the mountains at 90mph.  I'm thinking it should get over 50 if I bump it up to 110.

I've had my bike 23 years and 75,000 miles and generally expect 40-42, sometimes a little less and sometimes more depending on roads.

Typically around town I get about 37 mpg, but at the same time I only live about 7 miles from work and have several stops. I did check my mileage when I did my SS100 and I averaged 43.5 mpg. Granted a chunk of that time I was in the desert and hauling butt. including a few runs at/over 100. Once I made the turn around and came down south my speed decreased as there were a lot or towns and rural areas.

I haven't added any gas yet but I did just switch to reserve coming to work after 200 miles.

I haven't added any gas yet but I did just switch to reserve coming to work after 200 miles.

That's pretty much what I do too when just use it for back and forth to work.  10 miles one way, traffic lights and a little parkway and interstate.

Lot's of factors will affect gas mileage....carb maintenance, gas quality, winds, engine temp, speeds, etc.  My best fuel consumption was 52 mpg (avg 45 mph), worst 34 mpg (lots of twisting the wrist ), currently avg'ing 44 mpg (avg 65 mph).   I average around 240 miles between fill-ups....not using reserve.

FWIW: I put in an ounce of fuel stabilizer on each fill-up and run 2 ounces of Sea Form through the system about every 2500 miles.   Although some on the Forum may frown on using Sea Form; it has worked fine for me in all my engines...lawn equipment to automobiles!

40-44 for me.

40-44 for me.

   About the same for me.