Just recently, someone said the stock fuel line are unreinforced and liable to leak.  

Justin -

didn't you say that your MC was running rich (based on sooty plugs) before you went to the 155 jet? Sounds like your mix now is even richer than before. I don't know if this would explain all of the loss, but if I was trying to improve my gas mileage (oh guess what, I am), I would work to get the mixture right unless there was an obvious problem. An obvious problem would be loose valves.

I'm guessing most of the people getting over 50 mpg are running pretty close to stock hp also, which means pretty much stock air flow. I know when I was riding my Savage, I kept track of the mileage overall (over 5K miles) in all kinds of riding and got a little over 50 mpg. My MC was stock.

One thought, not related to fuel/air mixture, are you using regular gasoline or something with ethanol mixed. This affects mileage.

One more thought, what about your timing for ignition and valves? Is it possible things are stretched or out of whack?

Obviously how fast you ride and how much you use the throttle (stop and go vs steady mileage) makes a tremendous difference.

I'm running a 155 main with a sporty muffler and K&N drop in filter and I'm getting 55 mpg. I don't ride like a madman but I don't ride like an old lady either. mostly back roads and city riding.
AL

150 yielded about 42 MPG, with 14 baffles in the Supertrapp, stock pilot,1/2 white washer. I accelerate fairly hard & run up to 65 or 70 quite a bit, but not all the time. I dont spend a lot of time in town. I just think theres more to this than MY wrist on the throttle. I dont see any leaks anywhere. I have checked the vac line to diaphragm several times. I spose I can do it again..

My daughter has a pretty good nose. I'll get her to nose around the thing a bit. I HAVE smelled gas before, but cant remember if it wwas shortly after a gas station visit. Maybe I shoukd just replace hoses & see?

Also. have messed up & left it on Prime, & it didnt flood, so the float valve must be working fine. Ive been thinking about the fuel line being somewhat porous. If that were so, then the only fuel that could be lost is that in the line. When it's parked, the line would be al that could dissi[ate. I dont see that being enough to create a low MPG situation. If it was leaking bad enough to do that, seems I could see it sweat, if not drip. I am stumped.. Air cleaner has never been wet & is a K&N drop in. Waitin on a 152.5 main & I will be back in the carb. I will spens some time with a can O berrymans, blowing thru everything. I did notice a decrease a long time ago & it just seems to be getting WURSER & Wurser! I have even lightened up on the gas( When I remembered) & cant get good MPG.. The valves aren't needing service loose, just not as tight as I would do them if I adjusted. They arent even on 5, closer to 4 I betchya. I'll be in there in another 3oo miles.
Thanks to all for taking time to consider the options & respond..

Justin it really sounds like you have a problem, here. I am getting around 45-50 with a 155, K&N cone and I ride the throttle, and ride mostly in town. I think it is time to go through the whole system, I.e start at the airbox and end at the exhaust. making sure all the connections are tight, and all the passagways are clean.

Sumpin' just ain't right as they say.