40 miles to a tank? Help!

[flyingace]

I had sooty nasty plugs when my timing was off even though I wasn't running rich or using oil.

Well, then don't ignore this possibility!

[JHawkins]

JHawkins: Three gallons!

HOLY FU*&^%*&^(*&!!!!!!!!

Dude, that's a lot of fuel!

On the moosehead ride we were going between 80 and 110mph pretty much constantly and my 79 750L got 33mpg!!!!

I have my doubts that the jets could even flow that much fuel. and if it did, the bike would be so rich I can't imagine it running. Even the petcock would have trouble with those flow rates I would think!

[mooks420n]

Just got a '79 GS750L running after it sat for 5 yrs. I cleaned the carbs and tank up, put a new air filter in, sealed up the airbox and she runs. Can't see any fuel spilling out: Where do I start? I know she'll get better milage than this...
Thanks guys,
Wayne

If the petcock is not opening properly then you will feel like you are running out of gas,
Is there fuel left in the tank when you go to fill it up?

[KEITH KRAUSE]

'79GS750Lman, that old post Lynn put up is in response to another members problem. We were progressing and I suggested he make some additional adjustments on his pilot fuel screws, among other things.
The factory sets the pilot fuel and side air screws with expensive equipment. You can re-set these screws to near factory with some patience. If your bike is stock, the pilot fuel screws (underneath) can vary from about 1/2 to 1 1/4 turns out straight from the factory. If you have no idea where yours are at I'd try 1 turn out from LIGHTLY seated for starters. Use a good fitting tool to avoid stripping the head of any tight screw. Initially set the side air screws at 1 1/2 and then set them using the highest rpm method. They generally end up about 1 1/2 to 1 3/4 turns out. Again, be careful of stripping. If never moved, the air screws can be very tight. These adjustments will at least get you in the ballpark and any serious poor fuel mileage will not be the fault of these initial adjustments. You can fine tune the screws as necessary when the bike is running well which will probably require other tune up work.
Other areas in the carbs to check regarding poor mileage is the needle jet/bleedpipe (for clogged holes), dirty air jets at the carb throat/filter side, incorrect float levels (should be about .94"), loose jets, incorrect jet needle e-clip position (if PO changed?), yours should be at position 3 if stock, jets changed and now too large? Worn float needle valves can cause rich problems. Needle jet o-ring failing, etc.
After the carbs are set up correctly, at least bench synch the slides. I made a detailed post awhile back how to do that if you search? Once the bike runs better, vacuum synch with a vacuum tool.
You also must check the spark/ignition. Correct plugs? NGK B8ES. Gapped correctly.
Are the points clean and closing squarely? No pitting and uneven contact? Dwell must be set and then the timing. Check timing advancer action. Check all plug cap connections and coil terminals too. Check ALL connections for clean and tight. Check battery voltage and charge/fill with distilled water if needed.
Let us know how it goes.