Fuel Economy on a GS750

[hoyterb]

Brian Did you check the valve clearances?Too tight valves can do the same thing.
Brian H.

 

[Anonymous]

Brian Did you check the valve clearances?Too tight valves can do the same thing.
Brian H.

Good idea. I didn't check them because they were supposedly checked just prior to the previous owner parking the bike. It is probably worth it for me to do, because who knows if it was really done or not.

Yep... Sounds like rings to me too. You may have "stuck rings" though, not necessarily bad rings. If the bike only has 30,000 miles on it, it's hard to imagine rings being that far gone (and has it sat for some period?). My bike has about the same milage, and its compression is not that low

I think I'll give the berryman's a try. The bike sat for at least two years before I bought it, and then for another year after I bought it.

Thanks for the advice.

 

[earlfor]

Well Roger, I donno, something is screwy here. What year is your bike? CV's or slide carbs? I have my 750 set pretty rich, (the power is good and the engine runs cool....relatively) and I still am getting 45-46 to a gallon. Just a thought, are you running in 2nd and 3rd gear up and down hills around town all the time? Also, when I initially got my bike running, I thought it was running reasonably well. When I later got around to synching the carbs, I realized what I thought was running well, was actually borderline. The difference balancing the carbs makes is like night and day if they are very far out. The first time I balanced the carbs (when i thought it was running ok), the initial readings varied from about 15 inches to nearly 50 inches. Do you have stock pipes, carbs, airbox and sprockets? There has to be a simple reason why you are only getting 30 mpg.

Earl

Earl, my compression is about 150 across the board, and this fill-up I got only 30 MPG. This seems very low to me for a bike that really runs well now, and has no sign of sooty plugs and is not been "got on" much at all. I'm a pretty laid back cruizer on the bike. Most of my riding is "in town" commuting, and have yet been able to (find the time to) get it on the freeway for a tankful. Hopefully soon I will. Maybe I got spiders still living in the cylinders? Haven't synched the carbs yet, but plan to. They can't be too far off for how well it runs -- I' think. But hey, a motorcycle mechanic I don't claim to be, but it's really only the carbs on the bike that I'm foggy on.

Roger Moore

 

[Anonymous]

Earl,

It's bone stock. I typically run in as high a gear as I can without lugging it. Most of my commute is flat, so I'm always in at least 4th gear and accelerate smoothly through the gears. I've been meaning to synch the carbs -- and have the mercury carb stix to do it, but need the taps for the cylinders made. Just time. I'm sure they may be out some and I'm sure I'll be surprised by the improvement, which if it's running this good now -- look out Seattle!

Thanks!


Hey Brian,

Although it's true valves can cause low compression, squirting oil in the cylinder does not typically increase compression 40% if it's valves -- that's rings, my friend, or at least related to rings. And you said you saw a marked increase when you did this, by about that much. In the long run, it may be from the long sit -- especially if the previous owner didn't change the oil. Old oil can be quite destructive to an engine. It can essentially become an acid that eats away bearings and cylinders if it wasn't changed (accumulated sulfer from gas and oil mixing in the combustion chamber turning to sulferic acid :twisted: ) Not good. But let's not think that, just yet.

Roger

 

[Anonymous]

Roger:

I picked up a can of Berryman's on the way home tonight. It says to change the oil IMMEDIATELY after flushing the engine, so I'm going to wait to do that. Busy couple of weeks coming up. Anyway, I'll let you know if it is just stuck rings, or if it is something worse.

Thanks for the advice.

 

[saaz]

Best way is to get the mains right (flat out under load few a mile ot two, cut the engine then do a reading. Once the mains are ok you can try dropping the needles until you go one too far (will stutter, looks lean on the plugs). Then get the slow circuit right. Unfortunately the idle, slide cutout and needle circuits overlap. If the mods have upset things, to get it really right a chnage in pilot jet may help.

I have a 78GS1000, 1080 kit, stage 3 cams, ported head, 28mm carbs, race type pipe. I get around 16 to 18 km/littre around town and 20 km/litre on most trips. better than it was when standard!

GS750s were never great on the gas....they made a lot of power for their size relative to bigger bikes at the time, and are in a higher state of tune than the 1000s. Sort of like the GSXR750 of their time!!!