Ran for a good 2 miles, stalled, wont start.

[GoBlue]

My GS550 (no mods) seems to run fine for about 2 miles on a good day, then slowly but surely it seems to shut off its cylinders one by one, and die. It wont really start up again until everything has sufficiently cooled.

A little info about it... It sat for ~5 yrs. Carbs have been cleaned, new carb o-rings, boots seem OK. (I have ordered the intake o-rings, but not installed)

Other than that, its pretty much how it sat.

Upon cold start-up, 1 or 2 of the cylinders dont seem to fire right away, but after it gets going all the header pipes heat up, so I assume they are intermittent. I think it may be spark plugs and wires, just because the cylinders seem to die on me.

Im planning on changing plugs, checking valve clearance and installing intake o-rings, but can my description be pinpointed to something specific?

[Steve]

Upon cold start-up, 1 or 2 of the cylinders dont seem to fire right away, ...

Im planning on changing plugs, checking valve clearance and installing intake o-rings, but can my description be pinpointed to something specific?

If all your cylinders don't warm up right away, look for a pattern. If it is 1 and 4 or 2 and 3 that don't warm up, feel free to suspect ignition. If it is any other pattern, suspect the carbs.

You say you cleaned the carbs. Did you do the full "strip and dip" method or did you drop the bowls and empty a can of spray?

If you did manage to properly clean the carbs, I would suspect adjustments. Start with proper float height. You did not say what year your bike is (hint, hint, put it in your signature). The 550 had three different model carbs over its lifetime, they have different specs. When the float height is set correctly, move on to verify proper jet sizes. You do not specify whether you have stock airbox and/or exhaust, and suggested settings would depend on the presence of those items.

Other suspects: Do you have an in-line fuel filter? If so, what type is it, you might need to eliminate it. Most of the typical auto-parts store filters are too restrictive for motorcycle use. Have you tried opening the fuel cap when the bike dies? The vent might be clogged, preventing proper fuel flow.

.

[chef1366]

Petcock???????

[hjfisk]

I vote gas tank vent is plugged, only because he says it goes 2 miles then dies

[sedelen]

I vote gas tank vent is plugged, only because he says it goes 2 miles then dies

Could well be, if it's anything like my GS1000, there's a little itty bitty vent hole in side of the gas tank neck, if it is plugged, the pressure, provided there is any, will eventually decrease to where there's a vacuum reducing fuel flow and shutting the engine down. Cooling may give it time for the vacuum to relent if that is indeed what's causing the problem.
Just take off the cap after it dies and see if that makes a difference.

[GoBlue]

Its got Mikuni VM carbs, and I am pretty confident in the job I did on the carbs, however, I think its stalling from flooding. It leaks gas from the overflow, and wouldnt it bog down like that from flooding even at high speeds? Do you know which needle to adjust, even though I could probably figure it out?

I didnt know that about the fuel filter. I am using one from auto Zone or whatever, its about 1.5" in diameter. Looks OK to me, but I suppose you never know.

If all your cylinders don't warm up right away, look for a pattern. If it is 1 and 4 or 2 and 3 that don't warm up, feel free to suspect ignition. If it is any other pattern, suspect the carbs.

You say you cleaned the carbs. Did you do the full "strip and dip" method or did you drop the bowls and empty a can of spray?

If you did manage to properly clean the carbs, I would suspect adjustments. Start with proper float height. You did not say what year your bike is (hint, hint, put it in your signature). The 550 had three different model carbs over its lifetime, they have different specs. When the float height is set correctly, move on to verify proper jet sizes. You do not specify whether you have stock airbox and/or exhaust, and suggested settings would depend on the presence of those items.

Other suspects: Do you have an in-line fuel filter? If so, what type is it, you might need to eliminate it. Most of the typical auto-parts store filters are too restrictive for motorcycle use. Have you tried opening the fuel cap when the bike dies? The vent might be clogged, preventing proper fuel flow.

.

[GoBlue]

I have the 78' w/ mikuni VM carbs...

It started right up again after it sat for about 4hrs, so Id suspect flooding. I tried the gas cap (nothing really happened), and theres not an air vent on the tank that Im aware of.

I did find a disconnected hose on the petcock. The small line that connects the petcock to the middle of the carb body, (I think NO 2). No gas comes out of there though.

How does the petcock even stop working, I read a lot about those failing. Its just gravity right?

[7981GS]

That is exactly why it stopped getting fuel.

[sedelen]

That little line you found disconnected was the vacuum line from the petcock to the carb. Vacuum in that line "opens" the petcock diaphram which allows fuel to flow to the carbs. When the engine stops, it shuts off the fuel, with it disconnected it's like turning off your engine, stopping the flow of fuel, that is of course unless it's in "Prime"

[GoBlue]

Makes sense. Will it still start, because I bet ya it was disconnected for a while? I do mess with the petcock when Im trying to start it, so maybe Im just getting lucky.

That little line you found disconnected was the vacuum line from the petcock to the carb. Vacuum in that line "opens" the petcock diaphram which allows fuel to flow to the carbs. When the engine stops, it shuts off the fuel, with it disconnected it's like turning off your engine, stopping the flow of fuel, that is of course unless it's in "Prime"

[sedelen]

The Prime selection of your petcock allows the gravity flow of fuel all the time, switch it off when you're through riding though, otherwise you risk flooding your carbs and filling your crankcase full of fuel.

[GoBlue]

I may have gas in my crankcase. Is it a major concern? Ive read a few posts about it, but I probably havent ridden it even 5 miles yet.

The Prime selection of your petcock allows the gravity flow of fuel all the time, switch it off when you're through riding though, otherwise you risk flooding your carbs and filling your crankcase full of fuel.

[steve murdoch]

Do NOT start it until you have changed the oil, it is a major concern.
I would also check if you have gas in the cylinders. With the plugs out you may even be able to smell it.

[Gonzo]

I may have gas in my crankcase. Is it a major concern? Ive read a few posts about it, but I probably havent ridden it even 5 miles yet.

If you value your engine at all it's a major concern. Even trying to kick it over with a case and engine full of gas is a bad, bad idea. Liquid doesn't compress, and if your cylinders are flooded with fuel and oil, guess what is going to give up under that pressure first? I can promise you it won't be anything liquid.

Hook up the vacuum line so you don't have to horse around with the petcock, change your oil and filter if there is gas in it, and be done with it.