GS750L knocks when low on fuel

[Bill]

hi I have a 1979 GS750L runs awesome but knocks when its low on fuel. I put a bar up to the motor to See if the empty tank was amplifying a issue that was there and nothing but purring. I'm stumped!
I ride it daily and love it but don't want to do any major damish if I can avoid it.

[tom203]

hi I have a 1979 GS750L runs awesome but knocks when its low on fuel. I put a bar up to the motor to See if the empty tank was amplifying a issue that was there and nothing but purring. I'm stumped!
I ride it daily and love it but don't want to do any major damish if I can avoid it.

Maybe this is a prototype low fuel indicator!
Does the knocking change with rpms? Is your tank secure in the mounts?

[dakinejb]

My 81 1000 does the same thing. I actual like it, It lets me know when I need to flip to the reserve if I am not paying attention to my gauge. I have no idea if it is doing any damage but I doubt it.

[Bill]

it seems like it dos it at low rpm. I thought it was a oil pump going bad till my girl friend pointed out it whent away evrey time i got gas.
I probly owned 20 bikes in my 30 years of riding and never ran acrossed this.

[salty_monk]

Perhaps pre-ignition caused because it's struggling for gas & running lean...

Have you checked filters, fuel hoses etc for any restrictions? Is it a new petcock? Does it go away when you put it on reserve or prime? Pre-ignition (Pinking or pinging) is not good for your engine.... At it's extreme you can hole a piston.

[Suzuki_Don]

Pre-ignition (Pinking or pinging) is not good for your engine.... At it's extreme you can hole a piston.

Or more likely break the piston ring land and thump it into the valves making a real mess.

[Bill]

start running premum gas and it fixed the prolom

[cowboyup3371]

You don't need to waste the money on Premium as these bikes were made to run on Regular. All you are doing is changing the detonation point. I'd get in there and start checking things out like as already been suggested.

[Sunburn]

Maybe this is a prototype low fuel indicator!
Does the knocking change with rpms? Is your tank secure in the mounts?

What about the rubber mounts on the front, they fall off easy.

[Sunburn]

hi I have a 1979 GS750L runs awesome but knocks when its low on fuel. -

How low? are you on reserve?

[Eli69]

i had an odd noise when low on gas on my 81 650L. it was caused by the diaphragm on the petcock pulsating. the sound was amplified by the almost empty fuel tank. it lasted for at least a few weeks and then the petcock failed. the diaphragm was torn and had to be replaced.