82' GS1100GK Gas Mileage...25-26 mpg?

[tmacey45]

Can anyone please tell me what kind of MPG I should be getting from my 82' GS1100GK?
I just don't get it. I am getting around 25-26 MPG max (even less when I'm on her hard) which seems WAY too low to me. I have new plugs (NGK), all which are dry and a nice light brown. I have new plug caps and have trimmed wires back 1/4", new intake boots and O-rings, new fuel line, new fuel filter, stock airbox w/k&n filter, stock pipes, have re-built the carbs with all factory size jets (if memory serves me right 115 mains-40 pilot-and 60 air). I just put the carbs on sync gages today (right on the money, all are identical and read 200 kg-cm2). Bike runs, idles smooth and pulls like a train with no "dead" spots through power band. I have never had gas come out of the overflow tubes, nor the air box and there is no evidence of gas leaks any where. These GK tanks hold 5.8 gal (I think) and I can only manage around 130 miles on a full tank.
Any ideas on what may be going on? Thanks for any help...

 

[Nessism]

Only thing I can think of is the fuel level is too high so the bike is running rich and maybe leaving some in the airbox unbeknown to you. Of course the plugs don't show that so maybe not. Got a fuel level gauge? They are easy to make if you don't have one.

 

[979roadrunner]

Can anyone please tell me what kind of MPG I should be getting from my 82' GS1100GK?
I just don't get it. I am getting around 25-26 MPG max (even less when I'm on her hard) which seems WAY too low to me. I have new plugs (NGK), all which are dry and a nice light brown. I have new plug caps and have trimmed wires back 1/4", new intake boots and O-rings, new fuel line, new fuel filter, stock airbox w/k&n filter, stock pipes, have re-built the carbs with all factory size jets (if memory serves me right 115 mains-40 pilot-and 60 air). I just put the carbs on sync gages today (right on the money, all are identical and read 200 kg-cm2). Bike runs, idles smooth and pulls like a train with no "dead" spots through power band. I have never had gas come out of the overflow tubes, nor the air box and there is no evidence of gas leaks any where. These GK tanks hold 5.8 gal (I think) and I can only manage around 130 miles on a full tank.
Any ideas on what may be going on? Thanks for any help...

My 850, which is currently down for valve adjustment, was getting that sort of milage, probably becuase #3 cylinder wasn't firing, and I was using more throttle to compensate. (I know it wasn't firing because the header wasn't heating up) Are you hitting on all 4? Valve adjustment good?

 

[GSXXZRX]

Is this around town or highway.The reason I ask is because my Blackbird
gets twice the mileage on the highway as it does around town.

 

[tmacey45]

Only thing I can think of is the fuel level is too high so the bike is running rich and maybe leaving some in the airbox unbeknown to you. Of course the plugs don't show that so maybe not. Got a fuel level gauge? They are easy to make if you don't have one.

The fuel level is right on the money...about 1.5mm below bowl rim on all 4 carbs. I made a fitting and used clear fuel line to measure. I have had the air filter out several times, and it's always dry and no gas pooling at bottom of air box...And yes, the plugs are telling me all is right... I'm totally at a loss...

 

[tmacey45]

Is this around town or highway.The reason I ask is because my Blackbird
gets twice the mileage on the highway as it does around town.

It would be about 50/50 on the highway and around town...

 

[COGS]

My GK2 gets middle forties or more...have you checked cylinder compression? I once had a bike that developed a 25% loss on one cylinder for no apparent reason...TWICE! The manufacturer finally gave up trying to figure it out in the field, and just gave me a new engine assembly! One of the signs was an otherwise healthy bike that just all of a sudden started getting 25mpg...

 

[tmacey45]

My 850, which is currently down for valve adjustment, was getting that sort of milage, probably becuase #3 cylinder wasn't firing, and I was using more throttle to compensate. (I know it wasn't firing because the header wasn't heating up) Are you hitting on all 4? Valve adjustment good?

All 4 are firing, bike will idle all the way down to 500RPM, compression is as follows: cyl #1 117 psi cyl#2 110 psi cyl#3 115 psi cyl#4 110 psi with throttle wide open and engine cold. I don't have the specs, but I believe these were low compression 8 valve engines to begin with. Is 125 psi about right from factory?

 

[979roadrunner]

I'm not sure. on a high compression engine that'd be sorta low, but I'm less familiar with air cooled motors, which would need lower compression to survive.
If I had to guess, I'd say that sounded pretty good. Fortunately, someone on here will know, and we'll both be the wiser when the answer comes.

 

[Nessism]

Those compression numbers are low, but at least they are consistant. How about the valve adjustment? What kind of compression tester are you using?

 

[tmacey45]

Those compression numbers are low, but at least they are consistant. How about the valve adjustment? What kind of compression tester are you using?

Valve adjustment was done around 2K ago...As far as the compression tester type...???? I dunno. I borrowed one from Apex Motorsports which an employee is a friend. Scale was 0-200 psi. What were the factory specs on compression for this bike? I looked it up a while back and thought it was pretty low to begin with... like 125-130 psi unless I'm thinking of another model...

 

[Nessism]

Factory spec for compression on the 1000 model is 128 - 184 psi with a low limit of 100 psi. I'm sure your 1100 is similar. If the rings and valves are sealing the way they should the compression should be easily in the 170 psi range.

 

[tmacey45]

Yeah, I just looked it up too. Hmmm, there is no oil being used or burned. Perhaps I should check the valves again... I think I'll try a different gage first just to make sure pressures are correct... thanks for your input...