Poor fuel consumption from GS1000

[Guest]

I have a 1979 GS1000E which runs a Vance Hines exhaust, bellmouth stacks, Stage 3 dynojet kit, dyna coils and taylor leads. At the moment I am getting very poor fuel economy approx 20 miles to a UK gallon. That is at speeds between 70 and 80mph. Valves have recently been adjusted, timing is spot on and carbs have been overhauled. No signs of any leakage from the tap and no petrol leaking into the crankcase. Anybody got any ideas.

[chuck hahn]

Need to read the plugs. If they are black and / or sooty your way too rich. to lean it out, start at the bottom pilots with VM carbs. A colortune is your best friend here. I say this because doing the "highest idle" thing for me with my hearing is a true joke.

Once the flame color is right at an idle, you run her up to around 4,000 or so and adjust the side mixture screws till you've got the good blue flame at high RPMS.

Be sure the plugs are the right heat rating or maybe 1 hotter and they are gapped properly. Poorly gapped plugs waste lots of fuel.

Nip off about 1/4 inch of the plug wires and rescrew he caps on for fresh solid wire to cap connetions. Also unscrew the part inside the caps that clips to the plug and get rid of the resistors if they are still the old style caps. replace resistors with some brass or copper rod of the close diameter cut to length. This will actually give a hotter spark at the plug as well.

Float hts are also a consideration. If they are too high the carbs will run rich..too low and they run lean. Find that sweet spot.

Timing also has to be set correctly. And pods oiled too heavily act like a stuck choke and waste fuel at an alarming rate as well.

[gs79]

Thanks for the reply Chuck. I have a colourtune it shows a light blue flame at idle and also at 4000rpms. The plugs do look sooty. I have got the fuel screws will wound in.

[tkent02]

Almost three times the amount of fuel it should be using... that's pretty bad. Not just a little off on tuning, something is not working right at all.
The only times I have had fuel consumption that bad was when the carburetors had stuck floats and were overflowing going down the road. The overflow hoses dump under the bike, you won't notice it while riding unless it dumps a puddle in front of the tire while stopped and you notice some wheelspin when you start out again... or if it catches fire.
Are all of the plugs showing evenly rich, or is #3 richer than the others? This would point to a failed petcock diaphragm passing fuel into the #3 carb bore. It could dump a lot of gas.

What jets are in the carbs, and has it ever gotten good gas mileage with these jets?

Is the exhaust clogged? My 650 was down to 25mpg for a while with a clogged exhaust.
It also had some too fat main jets. Had the same problem on a GS 1000E with a clogged 4-1 pipe, some PO had jammed a bunch of steel wool down into the collector. Terrible gas mileage and no power at all.

You didn't mention how well it runs aside from the fuel consumption, how long it's been doing this, and what you hav done to it lately.

[gs79]

Thank you for the reply. Not getting any overflow from the carbs. Looking at the plugs they are evenly rich. The carbs are fitted with 140 mains. The engine feels fluffy from 3 to 4K revs then picks up cleanly from 5k upwards. The exhaust is only 8 months old.

[gs79]

Just wondering why all the plugs would show the same degree of richness.

[tkent02]

and carbs have been overhauled.

These overhauled carburetors ar the first place I would look. Who overhauled them? What all was done? What alll wasn't done? What all was done wrong?

I don't know the DynaJet numbers, but isn't a 140 main jet huge? The stock Mikuni main was only a 95.

[uk gs nut]

poor fuel mileage

Hi, Dave. I would say your main jets are to big, i would think 120 should be well big enough even with your bellmouths and pipe.
Dennis.