Poor MPG on XJ900

Been checking my MPG and I M only pulling about 31-35mpg. based on what I have read 44-47 should be more like it. I have a 26 mile commute one way, 10 miles 2 lane 16 miles interstate. Any suggestions?

 

check your air filter and your plugs to start

 

How long has it been since a carb clean and tuning? Look at your plugs, black is a rich mixture and wasting fuel. They should be a light tan color.

 

Air filter, plugs, VALVE CLEARANCES, FLOAT LEVELS, carb sync, even leaky enrichment plungers (not shutting off fully.)

How many miles on the bike and how many since you performed the services mlew and I mentioned? Last time you did a compression test?

Simply put; you're out of tune. Lots of things will add up to poor mileage; it's not likely to be a single cause (or fix.)

 

They are not great on gas.

 

I must have one of the better ones then, correcting the odometer error, 45 MPG, 40 if pushed hard. Holes in airbox cover, 4 into 1, carbs have never been off for inspection in 4 years, an ounce of Acetone (prevention) occasionally run thru, Synthetic/Dino blend oil, supposedly would ruin my motor, stored outdoors, what else am I doing wrong??

+1 on Fitz's suggestions on where to start,
Posting pics of your plugs would be good too.

 

Have a close look at the Enrichment Plungers.
Make sure that they are ALL closing and that the "Top Hat" portions atop the Plungers are Straight and NOT deformed causing the Plunger to not completely Seat and close-off Fuel.

Look at the Plugs.
If you have one or two that are darker than others; consider refinishing the Carb Diaphragm Piston Bores.

If the Diaphragm Piston is lazily returning to the Bottom of the Bore, ... While the Needle Valve remains suspended, ... you're wasting gas.

 

I get about 350 kms a tank (incl reserve!)

 

=37.65 miles per imp' gallon, as I said, not great.

 

Far enuff for me! Sorus Arsus!

 

To get extraordinary fuel economy from a 900 requires the type of discipline you'd expect from a Trappist Monk.

You ride the 900 like a little kid handed an ice cream cone during a heat wave.
Things start-off will all good intentions to savor the ice cream for awhile.
You wind-up biting that last bit of the cone and licking your fingers instead of taking any time at all.

When I get my 900 dialed-in; I often deliberately run in a lower gear just for the sweet-sound of the Mill at the top third of the power band.

Economically ridiculous.

 

I regularly use around 6l to do 100k's, stock except for 4into1. Don't normally ring it's neck but don't granny it either.