Poor gas mileage

[KJ790]

I am trying to figure out why I'm getting such bad gas mileage with my 81 XS650. I just rebuilt the engine (new pistons, rings, valves, cam chain) and had some mild porting done while it was apart. I have pod filters and a 2-1 exhaust with a pretty free flowing muffler.

I'm at sea level around 80 degrees F and I'm running 132.5 main jets with 42.5 pilots. I have my pilot screws out about 3 turns each. I believe these are the stock jetting specs for this bike, and everyone says that these bikes were jetted too lean from the factory.

The thing is that I can't even get 40mpg with this bike. Riding it easy the best I can get is 39mpg. If I ride it hard or if I have a head wind then I am down to 33-34 mpg. I'm not a big guy (165lbs) so I know that isn't the problem. The bike runs great and doesn't stumble at all at any throttle position. I have around 1,000 miles on the rebuild now, and I just put on a boyer electronic ignition, but my gas mileage is the same. I pulled the plugs and they look lean if anything to me.

Right plug:

Left plug:

Any idea why I can't get any gas mileage with this bike?

 

[TheRepairMan]

I never ever got any decent mileage with mine either ...not even when brand new! I had owned a few Volkswagens that got almost as good, and I wasn't a big guy either. I do recall some here saying the foam pods would mess with the jetting, though.

-R

 

[KJ790]

From most of the threads I've seen here it seems like most people are getting 45-50mpg easily. I just don't understand how I'm getting so much worse without the bike acting rich at all.

 

[5twins]

I would suggest inspecting and maybe replacing your needle jets. If they're worn, they will kill your mileage. You spend most of your time running in the midrange and that is what they control.

 

[Monty]

Hey, I know you from tt. I don't post too much over there anymore but I still visit all the time. I'm metalman1011 over there. Alright sorry for the thread hijack, just figured it is cool you also have an xs

 

[nateman15]

I've gotten 52 and then 54 on two consecutive tanks, the second being about 40 miles highway. I couldn't be happier. I am running the stock jets on an 81 650.

 

[tonytorque]

And how about mileage with mikuni vm34, Iam getting 18 km/ltr ,normal?

 

[DLD1]

Although my XS is a 79 with pod filters and 2-1 exhaust, I thought you would be interested to know that I went up two sizes on the mains, one size up on the pilots, and lowered the needle one step, and after freshening up my engine I'm getting 5-8 MPG better than when it was all stock. In stock form I was getting about 45-47 MPG, after the changes I've gotten as high as 56 MPG, and it's averaging around 52 MPG. The engine breathes so much better with the pods and 2-1 exhaust, produces more power, and you use less throttle, resulting in better mileage.
Good luck,

DLD1