81 GS450 Periodically Dies for Short Time

[Guest]

I have a 81 GS450 I have had for a few months. I am still working out the bugs so it can be a solid running machine.
After some initial work the bike was running pretty well. Ran it for around 1000 miles. In the last few weeks it had developed an annoying habit of randomly dying and won't restart or push start till is sits for 15-20 mins then it runs fine again. It has happened 3 times once it did it when it died at idle, once it did it when I turned it off for a short bit and tried to restart, and the last time it died on a ride as I was slowing for a stop light. Everytime it had to sit for 15-20 mins then started right up. It almost acts like a flooded engine.... What is annoying is that I cannot replicate it, so when I try to figure it out at my house where tools are handy to check my plugs and or see if the float bowls have fuel I have not been able to.

Any ideas what is going on?
Thanks,
Ryan

[chuck hahn]

Fuel has stopped flowing from the petcock. It sits for a while as what little bit that does trickle down refills the carbs.

Pull the main fuel line ( big nipple ) and hold a pop bottle up to the nipple and put it in the PRIme position..fuel should free flow and be as big as the nipples diameter..anything less is restricted flow. If it does flow and strongly, get a short piece of vac line and put the petcock in the ON position and suck on the vac line a little...fuel should flow as well as it did in the PRIme position..if not theres a restriction there.

If fuel doesnt flow well from the petcock, take the oetcock off and see that the filter screen inside isnt gunked up. Clean the filter AND do a thorough inside cleaning of the tank to prevent it from getting clogged again.

If all at the tank checks good then the problem is at the carbs..plugged fuel tee and transfer tubes ( if applicable ) and / or sticking float valves.

[hampshirehog]

Chuck's on it though it could also be a blocked vent in your fuel tank.

[chuck hahn]

more precisely..the caps venting. Can soak the entire cap in vinegar overnight and rinse it with hot tap water to break the crap loose.

[Nilson]

Ok, Thanks for giving me a starting point!
I will get at it and see what I can find.

[pete]

To test the fuel cap on the run, when it stalls out just take the cap off to let air in, if it starts right up there's your problem...

[tom203]

Carry a spare spark plug- easy way to make sure ignition system is ok. Next time it dies, pull a plug lead off,stick on spare, hold against engine and check for spark while cranking. No tools needed!

[Nilson]

Good tip Tom 203.

Well, I think I ruled out petcock and gas cap being issues. Took them both apart and they seem to be clean and functioning fine.
What would be the next logical place to look spark?

I just wish this dang problem was predictable... so hard to chase a intermittent problem.

[chuck hahn]

Bad connector or solder connection ( like at the back of the ignition for example ) ...gets heated up and then a micro crack opens just enough to break the circuit and causes a failure??? Like the one response suggested, carry a spare plug and go from cap to cap and see if theres spark.

Rarely see a coil heat up and fail..then cool and work. They usually are toast or work, but its not out of the rhelm of possibilities either.

Right where the connectors crimp to a wire are very susceptable spots for fails. Soldering them will often make good solid connections and eliminate fails. Thats just a few thoughts I got right now.

[chuck hahn]

And dont rule out inside the fuse box where the wires are soldered to the spades. I have found bad ones before.

[tom203]

Well, I think I ruled out petcock and gas cap being issues. Took them both apart and they seem to be clean and functioning fine.
.

Hopefully, you meant you tested petcock, not fiddled with it! Do chuck's test to absolutely rule it out....(30 year old petcocks can deceive you)

"Pull the main fuel line ( big nipple ) and hold a pop bottle up to the nipple and put it in the PRIme position..fuel should free flow and be as big as the nipples diameter..anything less is restricted flow. If it does flow and strongly, get a short piece of vac line and put the petcock in the ON position and suck on the vac line a little...fuel should flow as well as it did in the PRIme position..if not theres a restriction there."

[Nilson]

Well the fuel flowed fine in the prime position. I did suck on the tube in the on position and was able to pull the fuel with a reasonable amount of suction. I didn't pull the fuel too far down the hose because I don't really want to drink gas. In the on position the flow stops when there is no suction correct? Pulled the petcock from the tank and made sure the screen was clean. The tank is really clean looking. I reassembled and idled the bike 15 min which it ran fine. I am sure I will be out on a ride and it will randomly die and not start in the future though. That is how my life works.

[chuck hahn]

Suck gas???? You dont suck on the big nipple that feeds the carbs..you put a piece of vac line on the SMALL one and suck on it to mimmic the engine vacuum sucking the diaphram open like it would with a running bike!!! This will open the flow when the lever is in the ON position.

the petcock requires the suction to draw the diaphram back and open the flow in the ON position and in REServe. PRIme is just a bypass that allows a free flow to refill dry carb bowls should the fuel evaporate or you drin them for servicing the carbs.

They added a PRIme spot so you wouldnt have to crank and crank the battery down trying to refill the carbs.

[chuck hahn]

If you were sucking on the small vacuum nipple and got gas in your mouth the petcock is trashed..that shouldnt happen.

[Nilson]

I miss understood... I was putting suction on the big nipple not the small one.