Motor locked, gas dripping out of the cylinder

[Guest]

I just got the bike back riding yesterday and this morning was going to go for a ride. When I hit the starter button it cranked over twice then made a loud bang and moved the fairing with the force of it. Now it just clicks and will not turn the motor over. The valve cover and exhaust outlet are dripping gas. I pulled the spark plug on that cylinder and is was soaked in gas. I left out the plug to air it out.

Where do I go from here? I am worried that the engine is toast.

[Nessism]

Rebuild the carbs, verify float valve operation using a piece of clear tubing, and check your petcock. May be leaking fuel down the vacuum line and into the carbs/engine.

Carb rebuild tutorial linked in my signature.

[robertbarr]

The cylinder in question had filled with gasoline (relatively incompressible) before its compression stroke. When it reached the compression stroke, it simply cannot travel any further.

With the spark plug out, you should be able to turn the engine over. Don't use the starter! That will will force a few ounces of fuel out of the spark plug hole at pretty high pressure. (And your ignition will be functional!) I made this mistake once, and it sent a fine mist of fuel all over my garage. There were little droplets all over a window pane that was six feet away. If I had had a water heater out there with a pilot light, Va-VOOM. Incredibly stupid move on my part, almost invoking Darwin.

You can also wait a bit and allow the fuel to pass slowly past the rings, into the crankcase. Or: Remover the ignition cover and crank the engine with a wrench, which will force the fuel out of the spark plug hole in a controlled manner.

Obviously, you then correct the source.

[Nessism]

With so much fuel in the cylinder, you may also have a some sitting on the bottom of the crankcase, mixing with the oil. Time to check oil level and plan for an oil change, maybe two of them. Diesel engine oil is great for GS bikes, and is reasonably cheap too.

[LSCCOLT]

After letting the bike sit overnight and all day I was able to get it to turn over. I did not want to start it because of gas most likely getting in the oil. So I am confident it is a carburetor issue. I do not know if it needs a full rebuild on the carbs or not because it is just the one.

Also I noticed that the petcock has no OFF only ON, RES and PRI. It was in the PRI position, could this have been why it flooded? I assume it is for prime and would push extra gas to the carbs right?

I just want to make sure that the carbs are the problem before I pull them off as I do not want to mess with them because I am pretty sure they were recently rebuilt.

Thanks for the help.

[chuck hahn]

ON is OFF when the bike isn't running. The vacuum stops when the engine stops and the diaphragm closes an Oring against the bore to shut off the fuel.

So, as you've already guessed, leaving it on PRIme doesn't shut off the fuel EVER and thusly that was why they flooded. Change the oil, set it to ON and ride on. No harm no foul unless it happens with it in the ON position which would indicate a bad petcock.

[LSCCOLT]

Thanks chuck hahn, I am going to grab some oil tomorrow. I am glad it was an easy fix. No one to blame but myself for that haha

[chuck hahn]

Youll do it many more times. I just did it a few weeks ago on my 78 1000C. Got messing with other crap and forgot to turn the petcock down again..chit happens.

[chuck hahn]

Didn't lock a cylinder but I had plenty of gas in the oil and some under the bike!!! Dripped out the airbox and made a nice area under the bike wet.