Bike stalls after 5 minutes

[longranger44]

So I put brand new Keyster float valves in my 82 gs750t, a rebuilt petcock, as well as an o ring kit courtesy of Nessism (great kit, great price and super fast shipping I might add), and the carb leaking into the air box and onto the ground problem is gone. The bike starts fine and idles normally when cold, but after about 5 minutes or so the idle slowly starts to fall until the bike stalls out completely. I'm a bit perplexed as it never did this before, any thoughts on what could be causing this? Thanks in advance!

[Rob S.]

I'll guess petcock.

[tom203]

Yes, just get a new petcock and rule it out as a problem….

https://www.ebay.com/itm/201646389696?mkcid=16&mkevt=1&mkrid=711-127632-2357-0&ssspo=AH0MSk6DRbK&sssrc=4429486&ssuid=ARSR0K5ISZu&var=&widget_ver=artemis&media=COPY

[Rich82GS750TZ]

Before you do that, Check the gas tank cap vent. After the bike dies, remove the gas cap. If you hear a wooshing sound, like a vacuum release, your cap is not venting properly and not allowing the petcock to flow fuel properly after running for a few minutes. Or just run the bike w/out the gas cap in place. See if if still dies. Cap can be carefully disassembled and cleaned, but the only way I've found to replace a worn seal is to buy a cheap cap for your bike on ebay and swap out the ring seal.

You don't mention using choke it all. If starting the bike on choke, revs should go a bit high. incrementally reduce choke over a few minutes till the bike idles. Idle speed (the knob under the carbs) should be set to about 1100 rpm when the bike is warm.

[rphillips]

Quickest simplest thing, put petcock on PRI. and see if things change. On PRI. the vacuum and working parts in the petcock are bypassed.

[Rich82GS750TZ]

But even w/ petcock on Prime, if the cap vent is clogged, gas won't flow properly.

[rphillips]

All good to check on, but thinking cap vent will take way longer to create vacuum in tank. Think how little the volume of gas in tank will change when idling for 5 min... No doubt got to check everything.

[Rich82GS750TZ]

I don't disagree with your thinking at all, rphillips. I just go to the least expensive things first and rule them out.

[rphillips]

I Like your thinking, cheapest, easiest things first... It's amazing how often you won't need to dig into the bigger stuff.

[longranger44]

Before you do that, Check the gas tank cap vent. After the bike dies, remove the gas cap. If you hear a wooshing sound, like a vacuum release, your cap is not venting properly and not allowing the petcock to flow fuel properly after running for a few minutes. Or just run the bike w/out the gas cap in place. See if if still dies. Cap can be carefully disassembled and cleaned, but the only way I've found to replace a worn seal is to buy a cheap cap for your bike on ebay and swap out the ring seal.

You don't mention using choke it all. If starting the bike on choke, revs should go a bit high. incrementally reduce choke over a few minutes till the bike idles. Idle speed (the knob under the carbs) should be set to about 1100 rpm when the bike is warm.

I hadn't even thought of the gas cap. I tried again today pulled the cap off as it was beginning to die, unfortunately it made no difference. Good thought though it never even occurred to me.

[longranger44]

Ok so I started the bike again today and here is the sequence of events-
On full choke it fires immediately and immediately wants to Rev to the moon on full choke, turning it down to about half choke brings the idle speed down and the choke can be turned off completely within 10 seconds or so. It then idles around 1100 for a few minutes but gradually climbs to 1500 around the 5 minute mark and stays there. Then around the 8 minute mark it gradually begins to slow until it stalls out completely.
Once it's stalled it can be restarted immediately with a bit of throttle and it will idle for 20 seconds or so before it stalls out again. Also, if you blip the throttle as it's trying to stall, it goes back to idling normally for 10-15 seconds before stalling out. This can continually be done to keep it running which I thought might be notable. I took a video of this in case it means anything to y'all. Let me know what you think and thanks for the help so far!

[Rob S.]

(Intake) air leak?

[tom203]

”Ok so I started the bike again today and here is the sequence of events-“

The sequence is odd. Being able to turn off choke after ten seconds and hold idle is odd for a cold motor . To me this suggests that engine is getting a extra fuel dose from somewhere ….but this eventually dwindles and bike stalls until blipping the throttle restores this extra fuel dose..somehow .
make sure your petcock works on PR…test it and reconnect to carb fuel rail….disconnect and plug vacuum line to carbs.

[longranger44]

”Ok so I started the bike again today and here is the sequence of events-“

The sequence is odd. Being able to turn off choke after ten seconds and hold idle is odd for a cold motor . To me this suggests that engine is getting a extra fuel dose from somewhere ….but this eventually dwindles and bike stalls until blipping the throttle restores this extra fuel dose..somehow .
make sure your petcock works on PR…test it and reconnect to carb fuel rail….disconnect and plug vacuum line to carbs.

Ok I disconnected the fuel line and With the petcock on prime it flows fuel freely, with it on "on" it shuts fuel off but not 100%, it will slowly drip like one drip a minute. Same with reserve.
I tried turning it to prime while it was running and there was no change in the stalling behavior. I'm not sure what you men's by plugging the vacuum lines?

[chuck hahn]

Be sure the fuel line isnt kinking when you set the tank down after hooking up the lines. Check the vacuum line going to petcock also.may be leaking vacuum.