'75 REALLY Bad Gas Mileage

[ericheath]

Check front and rear rotors for heat indicating dragging brake pads. It doesn’t take much to pull you mileage down.

[Gowing]

My 75 gas gauge works. Just lucky I guess.

[Kingpin06]

I just went through that very thing with Janis.#2 float needed to be readjusted. I had just went through the carbs, and I tested them on the bench, ran it some,was running pretty well, but was getting maybe five miles to the gallon. Pulled the lid in the breather, turned the key on. The electric pump I had just installed, and there it was left rear cyl. I snuck the bowl off,set the float ,and now it's running almost perfect.

[Kingpin06]

That engine will take a lot of fuel before it starts running bad.

[Dr. Frankenstein]

A bit of a follow-up: I took the bike out yesterday for an extended ride; I filled it up to the neck, reset the odometer and planned to ride until it stuttered and then switch to the Reserve and do the math to figure out my gas mileage.

One of my friends said it felt like the bike was missing, but it seemed to accelerate and idle just fine. So we hit the road and rode several very nice backroads around here until they needed to stop for gas so we did; I thought the bike ran great. I had 66 miles on the odometer. I had a nagging feeling that I too should fill up, but with just 66 miles on the clock I really wanted to test the assertion that the gas gauge was "for entertainment purposes only." We started back out, and I got probably no more than a mile before the bike started stuttering, so I switched to Reserve but that didn't help. I coasted to a stop and we took a look at the problem. No gas to the fuel pump.

I took a look in the tank and it Appeared to be almost empty! I could see the top of the little lower 'cage' or whatever it is in the bottom of the tank. My friend - who Does know his way around a motorcycle engine - thought it was a case of vapor lock and we tried to get the Reserve open, to the point of blowing into the tank to create some back-pressure in case there was something blocking the Reserve line, and it Did work, briefly. But I told him that it was simply out of gas. We added some from their bikes and I rode back down to the gas station and filled up. The bike ran fine for the 16 mile trip back to the house.

On the way back I thought about the problem, and thought Maybe I had accidentally put the petcock on Reserve the whole time, but that was not so, the switch was where it should have been, in the 'Run' position/straight down.

They had also commented on how rich the exhaust smelled, and I noticed it too, so obviously I think it's running rich - REALLY rich! 66 miles to the tank is Not Good. The carbs are set to three turns out, I know this for a fact because that's where I set them per recommendations in the Forum per Mike Nixon, and I haven't pulled the plugs to take a look yet, but I'm pretty sure they're going to be black; I believe the No Reserve problem may be because of a clogged line in the tank.

I have not yet checked the needle jet for height, but that's on the To-Do list; IIRC I did check the needle height when I rebuilt the carbs, but I will check them again, along with the floats which I had set to 21mm. So what am I missing? One of the things I can think of is that if indeed it is missing, maybe I was getting a whole bunch of unburned fuel through whichever cylinder may be missing, but I *had spark at all four cylinders when I buttoned it up...On the "Plus" side of things though, this is what this trip was for, a shakedown run to see what what's what and what needs to be paid attention; so what should I check and what am I looking for? And while we're here, what's a good way to clear those tank lines? 66 miles for the tank is REALLY bad gas mileage!

[gltriker]

John.
When I was prepping my GL1000 fuel tank for the install of a POR15 kit back in 2012, I utilized a length of the broken clutch cable removed from my GL1000. Although I hadn't checked for restriction in either fuel supply tube circuit before starting the fuel tank refurb, I felt it would be foolish not to at least mechanically ream them .

I eventually discovered a splayed end, clutch cable was too inflexible going forward in the reserve supply line, to continue beyond an oddball arch hidden under the primary fuel supply's, pickup screen. The clutch cable was successful to destroy that particular screen and expose the unexpected oddball arch.
The most commonly recommended reaming utensil is a much more flexible section of throttle cable. At least for reaming the entire length of the reserve supply tube..

see my post #62 in this link
viewtopic.php?f=30&t=39996&start=60

In addition to removing the fuel selector valve, it is a Best Practice to refurbish the internal and external sealing components of that fuel valve assembly, too.( I can't remember whether you had obtained the Randakk Kit, or not. )

I had a situation where, even though I had rebuilt the valve assembly with the Randakk kit bits, unbeknownst to me the internal valve disc had deteriorated and I would 'run out of fuel.'

see my post#247 in this link
viewtopic.php?f=30&t=39996&start=240

[gregforesi]

Check the oil level and take a sniff.

[Sidecar Bob]

^^^ Good suggestion. Really, really good suggestion.

My 75 gas gauge works. Just lucky I guess.

My '77's fuel gauge always took a while to start showing that the level was decreasing after filling it up but it always needed to switch to reserve just where the gauge said it should and my '83's gauge was the same.
The delay in starting to indicate is caused by the shape of the tank; The area around the filler is higher than the part under the seat and the higher part holds a litre or so. The sender's float doesn't reach into that area so the gauge won't move until you have used a litre or so and the level drops where the float is.
I don't care about that much as long as the gauge is accurate when the tank is low because that's when you really need to know.
BTW: My '83 currently has a Danmoto instrument panel and when I installed it I tweaked the sender's arm slightly so that the gauge starts to flash (indicating low fuel) very slightly before I need to switch to reserve so that I'm expecting it.