Engine Knock

[Guest]

i have 83 GR650 Tempter, when it gets low on fuel the engine starts to tick or knock... kinda sounds like the valves need adjusted, but once you fill it up with fuel the knock goes away till u go about another 100 miles then the knock comes back... any help on this one would be appreciated

[Nessism]

Maybe the fuel sending unit is making noise. You need to isolate the noise to the source before you can figure out what it is.

[TyFerris]

sorry if this is a dumb question but can you explain the fuel sending unit to me... and how would i isolate that to see if its making the noise

[airbornespud]

an easy way to find the source of the noise with the engine running is to use a stethoscope with a metal rod shoved in the end of the tube instead of the cold pickup the doctor sticks on your back to listen to your lungs. place it firmly against different areas of the bike where the noise seems to be coming from. the louder it gets, the closer you are to the source of the noise. sometimes you can isolate it down to a specific cylinder or even valve, if it's in the engine, or the fuel sending unit, using this method.

[Nessism]

The fuel sending unit is for the fuel gauge. There is a float on a movable arm that sits on top the gas in your tank, and the float moves up and down with the level. Maybe the movable arm is banging around inside the gas tank when the fuel level is low? You can try removing the fuel cap when the bike is making this noise and listen inside for noise. Failing that, you might want to rig up a remote fuel tank, after removing yours, and listen to the engine that way. Good time to check all the valves and cam chain tensioner too. We trust you are performing maintenance like a good GS owner would, so it never hurts to perform this kind of check.

Good luck

[Mekanix]

Sounds like it needs the carbs cleaned.

[7981GS]

Perhaps when it is close to empty it is drawing some of the WATER that is in the bottom of the tank and lowering the octane number?

[TheCafeKid]

Did someone bring in some Bud Lite? Cause "Here we go".....

[tom203]

Perhaps when it is close to empty it is drawing some of the WATER that is in the bottom of the tank and lowering the octane number?

Wouldn't it be drawing the octane reducing substance at all times-not just when almost empty?

[7981GS]

Pour one once of water into a glass jar that is half filled with gasoline and report back on your results.

Eric

[apopleptic]

I have a similar noise on my bike. the knock is actually coming from the stator area and it just echos up through the gas tank as if it were a speaker.
Buy a mechanic stethoscope from harbor freight or somewhere and use it to locate the exact source of your knock before you go crazy. It's a very well spent $3.