For those of you who don't know, I've got an '84 Yamaha FJ600 that up until 2 weeks ago didn't run. I've replaced all spark plugs, as well as the starter relay, and changed the oil. After tweeking the throttle assembly and idle screw I'm able to ride it. The carbs are NOT synced yet.

I'm currently getting about 20-25mpg on a bike that should get closer to 55. Wet wait, w/ me on it we're talking about 575lbs.

I've noticed that there is a bit of gas being spit out the back end of carbs 1 & 4 (esp 1), and it has to idle at about 2K to keep from stalling. When I'm starting off in 1st it doesn't have a lot of power, but goes well, then it hits about 3K and has a power spike. Then I go into second, and it's fine from there. Finally, it seems to have plenty of power for such a small bike, but the fastest I've been able to get it is 75 +/- 5. At 55 the RPMs run at about 6K.

I'm a new rider, and am trying to get this bike running smoothly on a budget. I plan on rebuilding the carbs, and getting them synced up, as well as having the valves adjusted, but does anyone have any ideas on what I can do in the mean time to get better mpg?

Thank you,
Mark

Sorry I got no shortcuts for ya, you'll never get good fuel mileage without clean, non-leaky, balanced and adjusted carbs. 20 MPG is pretty bad but if your carbs are leaking fuel or dumping excess into the chambers that's to be expected as your just throwing away fuel.

Rebuild, clean (really good), tune, and sync your carbs. Adjust your valves. Make sure your oil doesn't smell of gas, if it does change it. Then you'll have a good running bike that gets good MPG.

Yeah, i figured that's what it would need. I don't mind it so much right now, and planned on doing all of that anyway. I was just hoping there might be a quick, short-term fix to get some better mpg in the mean time. No worries though. I'd rather ride my bike @ 20-25mpg than drive my car @ 25! Thanks for the help.

From the sound of it, your carbs really need a complete rebuild or replacement.