Bad mileage on 78 750.

[civiljar]

Hey, Longtime lurker, first time writer. I've got a 78 750E. Ive been riding it for about two years and gotten consistantly decent mileage (in the 45-50 range) However this spring I had some issues with moisture getting into the gas and gumming up the works . A combo of a loose gas cap and condensation from sitting for two weeks while I had a medical procedure.

I had a rather spectacular breakdown/overheating issue (white smoke issuing from the left side etc.) I drained the carbs and added some dry gas to clear up the moisture. But since then my normally smooth running bike has been running funny and using twice as much gas. I'm getting about 25 MPG. I'm replacing the intake boots and checking the valves to see if they went out during that whole thing. Am I headed in the right direction? Has anyone else had a similar problem? Is there an easy fix? Any help would be much appriciated. Thanks,
Adam

 

[GSX550]

If you have overheated the bike, then it may pay to check the compression. While overheating an air-cooled bike is not in the same vein as overheating a water-cooled bike, you may still have done some damage that could have reduced the compression on a few cylinders.

This could explain you poor economy.

 

[TheCafeKid]

Hrmm. Just a suggestion as well, along with some observations: 45-50 mpg, depending on how heavy wristed you are, sounds a bit on the lean side for a 2v GS. Not saying it's the case as many things contribute, but you may check that. Also, when's the last time you've adjusted your valves? This can cause compression issues, obviously, as the valves in the 2v heads tend to get "tighter" with wear and would cause the valves not to close all the way. Compression would obviously be reduced, making things leaner(er) as well. This would/could require more "wrist" to get the power you're used to getting, and reduce fuel economy by a bit. Valve clearance checks/adjustments should be made every 3-5 thousand miles, and are standard maintenance items. Before you can do an accurate assesment of compression levels, you'll likely want to check your clearances and adjust them as necessary.

 

[civiljar]

Update.

Update.

Thanks for the help. I had one more overheat tracked it down and it wasn't a fuel/carbs/compression issue at all. My clutch was gone and slipping, cooking up the oil, and giving me terrible milage. New plates are on the way and should fix this.

 

[D-VO]

Hey at least you found the problem!

My motor could probably be classified as "iffy" at best. My compression is low, around 100-105psi, It's running super rich, I'm only getting around 29-30mpg, and lately it's been starting to smoke light blue a bit. I'm torn on where to start. I like riding it too much to really tear it down during the summer.

 

[tkent02]

Repair the carbs to get rid of the rich problem, it is ruining the engine. Fuel washes oil from the cylinders, lets the rings and the cylinder bore wear, soon you will have a bigger problem.

 

[D-VO]

Oof, that's a job I'm not looking forward to. I think new jets might be in order first.

 

[tkent02]

Then keep waiting and rebuild the engine.
It's up to you.