79 GS1000L on the best coast

[Ice]

Hello everyone. Thanks for this great resource!
New 79 GS1000L owner here. Got a freebie from a friend. Yes, a very good friend with a heart of gold.
This bike needs some work but it rides. Biggest issue is the gas mileage is like 10-14 miles per gallon. Yes lots of power but I want to bring it to around 40mpg or better if possible. Will be looking for answers on the forums here but if you know what could cause it to be so low feel free to point me in the right direction. Thanks!

[Nessism]

Wow. I think you win the world's worst gas mileage ever contest for a GS bike, this side of a pro stock drag bike. To solve the problem, I suggest checking to see if your carbs are leaking straight out to the ground via the overflow tube(S). Failing that, start at the beginning by doing all the various maintenance tasks. Good luck

[rphillips]

Not a clue about anything but a "79" GS1000 L, first thing to look at is the air intake system. Filter needs to be reasonably clean & in place. Be sure the usle+%&#**?&^ cable operated choke (starter) control is completely closing choke rail. Not a clue if it's been sitting a while, but if all is not connected properly, mice beds have been found in air boxes, boots, & carbs, Hopefully something kind'f simple... Oh Yeah, Welcome & good luck.

[Ice]

Looks like they plugged the overflow tubes. And it has a 4-1 exhaust.

20220809_111822.jpg

[Ice]

Probably should throw a USA flag on the back there .

20220809_111641.jpg

[rphillips]

Ohhh, be careful, no chain guard. Be sure not to do bell bottoms or dangling shoe laces... Very good friend?? heart of gold??? yep, I'd say so.

[Ice]

Thanks rphillips, this is my first bike that's not shaft driven.

[Nessism]

The plugged hoses are vents. They should be open, BTW. The overflow tubes are on the floatbowls.

Something else looks wrong: there should be a center Tee in the carbs, which connects to the fuel cock and feeds fuel to the carbs. The 2nd largish hose, with a fabric covering, looks out of place. Where is that running? And lastly, there needs to be a vacuum line running from the carbs to the fuel cock also. That hose is small diameter. Maybe someone installed a manual petcock and ditched the vacuum line?

[Ice]

I unplugged the vents and the fabric covered hose is the vacuum hose connected to the carb. There are no overflow hoses on the bottom of each float bowl. Where are the other ends supposed to drain to? Thanks!

[Rich82GS750TZ]

This pic should help you sort your hose connections.

[Ice]

Thanks Rich! I'll need new overflow hoses and longer vent hoses but other than that it looks fine and no leaks. I checked the fuel petcock and it work with no leaks. Maybe the next step is take the carbs apart, clean and inspect. Would just the wrong jets be the cause of such low fuel mileage?

[Rich82GS750TZ]

No idea. But a full clean is never a bad idea. Full VM carb clean and rebuild tutorial is on BikeCliffs Website. Link in my signature. In the right column, bellow the wiring diagrams.

[Rob S.]

Would just the wrong jets be the cause of such low fuel mileage?

Wouldn't wrong jets (or similar carb factors) of such magnitude (25% mileage) be noticeable at the right wrist, 'seat of the pants'? Be nice to get the dyno numbers, or some dragstrip figures.

[Nessism]

Thanks Rich! I'll need new overflow hoses and longer vent hoses but other than that it looks fine and no leaks. I checked the fuel petcock and it work with no leaks. Maybe the next step is take the carbs apart, clean and inspect. Would just the wrong jets be the cause of such low fuel mileage?

To get 11 mpg, due to the wrong jets, the jets would have to flow so much fuel that the plugs would foul. Also, there would be a LOT of black smoke out the muffler.

The choke plunger seals could be leaking, causing a rich running condition. Even at that, though, you won't get 11 mpg.

[Rob S.]

To get 11 mpg, due to the wrong jets, the jets would have to flow so much fuel that the plugs would foul. Also, there would be a LOT of black smoke out the muffler.

The choke plunger seals could be leaking, causing a rich running condition. Even at that, though, you won't get 11 mpg.

What I meant. If it's actually running all that gas through the carbs, you'd never get acceptable HP/torque numbers. It's not missing or coughing?

If it's not smoking, fouling plugs, lagging in performance #'s, it's pretty much got to be dumping it out on the tarmac somewhere, no?