Can I ask how you are measuring your mileage? We've had a couple guys that were going off the fuel light and were getting perceived low mpg.

 

+1 everything that's been said, start simple, air filter, plugs, tire pressure, give the exhaust a good whiff. Also check for vacuum leaks.

 

Thanks for all the replies!

I measure mpg by odometer miles divided by gallons each time I refill.

The exhaust does smell slightly like unburned fuel.

I changed spark plugs yesterday, the ceramic on the old ones was not discolored, the metal looked O K to me, but not an expert.

I washed the air filter in warm soapy water and it looks much better. It was visibly dirty plus filled with bugs!

I don't have a tool to measure head temperature yet.

Lastly tire pressure is correct.

 

For reference, does the appearance of these plugs tell a story? Dumb question... there are only two plugs on a sportster right? One per cylinder?

https://i.imgur.com/sf0FYPG.jpg

 

Here's my experience with fuel mileage on my 05 Roadster 1200, 3.3 gallon tank:

All in-town driving, stop lights, traffic, rarely ever hitting 3rd gear, +/- 30 MPG
Mix of in-town, Interstate, highway driving, +/- 42 MPG
All Interstate and Highway, +/- 53 MPG

I've learned to refuel after 75 miles to 130 miles. All depends on the roads I've travelled on since I last filled up. I measure the same as you, by fuel in divided by mileage.

 

It tells me you should resize your photos so they don't blow out our page.

 

Hah, despite the sizing, your plugs look fine. It is REALLY hard to read plugs these days. That's about as good as you can get them without having serious problems.

 

Edited the embedded picture to be a link.

Thanks for the ideas everyone.

 

A Sporty has four plugs!!!

When you buy new sparkplug you'll notice that they come in packs of two. Now, for your Sportster you will need two packs (one per cylinder) in general I find it best to, when you change the top sparkplug, also change the bottom one. It is not unusual that when you don't, the firing on the "up"stroke gets a little weaker.
When that happens, your front and rear pistons start to misalign. It happens a lot and specifically with slightly older Sportsters (pre- 2007). This can be the reason for excessive vibration specifically felt through the handlebars.

Make sure that you use the same pack for the same cylinder as these plugs are "paired" for better synchronous firing.

 

I'm not sure what sporty you're working on, but mine definitely has two. I believe that there were a couple models with four but to my understanding almost all sporty's have two.