Gas Mileage Part III

Spoke to the mechanic working on my '85 Maxim XJ700, says can not find any obvious reason for poor gas mileage, sz seems to be a knock off Mikuni style carb that Yamaha used and jet size had been changed to 107 from 100 but it should not account for around 25 mpg, there is no indications any where else of a problem.

This bike is pristine, but the gas mileage sucks... may sell and buy something else, not sure what else to do.

 

Mine has fallen from Mid 40's to around 34. Need to synch the carbs i know, but 25 seems pretty low to me.

 

I would get the bike back from the shop and do the work yourself. I personally don't trust any shop to work on my bike mainly because of its age and most mechanics out there don't know about how to tune our bikes correctly. Once you are used to the construction of the carbs they really aren't that hard to deal with. Have you had the bike tuned; Carbs cleaned well(taken off the bike and taken apart, check rick-co-matic's carb cleaning thread), synched, and fuel to air mixture set? This will go a long way to figuring it out.

I would start with this. A motor is not going to give you efficient gas mileage unless its components are maintained and tuned correctly.

 

What about your compression?
How do your plugs look?
Valves have been adjusted?
Fuel is not dripping out of the carbs, PCV, petcock, somewhere in your crankcase oil?

There is an answe to every problem, you just have to find it first. Good luck

 

Thanks for all of your responses, I passed the info onto the mechanic who now has my bike. 3 of 4 plubs were carbon black, 1 was reasonably brown, I'll ask about the rest.

He says he has not noticed any other problem, I am no expert, thus need to rely on what I'm being told. As my avatar suggests, I'm a wannabe!

 

Actually, it says you're a gear grinder. Patience, grasshopper. Knowledge will come to those who seek it.

 

My float levels were off just a smidge, and #2 was always rich.
I pulled the carbs to fix a leak in the inlet line and while I had them off I adjusted the float levels.
It made a big difference in the mpg...went from about 37 to a pretty consistent 45mpg.

As TMHack suggested, you need to bite the bullet and learn how to work on them yourself. There are precious few mechanics out there anymore that have a clue how a carb works much less how to clean or adjust them. You will give them a bunch of money and never get it fixed.

Don't be afraid...There are not many parts in them and with a little patience and guidance from this great web-site you will be a carb cleaning and tweaking wizard.