Bike stalls after 5 minutes

[longranger44]

All good. So didn't touch the pilot screws? Did you replace the seats or just the needles? Did you re-check the float levels after fitting the new needle valves? There's no guarantee that the Keyster part is the same length or has the same spring tension on the plunger pin as the part it replaced. Bowl level also affects mixture. If it were me, I'd look at the plugs, its a tell-tale whether is getting too much fuel or not enough when it stalls.

The pilot screws are easily accessible with the carbs installed in the bike just by taking the tank off so I figured I could mess with those later if necessary. Do you think that'd be a good thing to just do?

[longranger44]

So I think I've ruled out the petcock/tank being the issue. I fashioned an auxiliary "tank" from a plastic bottle (just a bottle with a vent and a nipple) and disconnected the fuel line from the motorcycle tank while the engine was hot, right after it had stalled out. With the new "tank" connected the bike behaved identically to when it was connected to the actual tank.
Am I correct in thinking this rules out the petcock/tank and that this must be a carburetor issue? If so, what would cause it to slowly stall out only after it gets hot, but can be made to keep running just by blipping the throttle every 10 or so seconds?​

[KiwiAlfa156]

So I think I've ruled out the petcock/tank being the issue. I fashioned an auxiliary "tank" from a plastic bottle (just a bottle with a vent and a nipple) and disconnected the fuel line from the motorcycle tank while the engine was hot, right after it had stalled out. With the new "tank" connected the bike behaved identically to when it was connected to the actual tank.
Am I correct in thinking this rules out the petcock/tank and that this must be a carburetor issue? If so, what would cause it to slowly stall out only after it gets hot, but can be made to keep running just by blipping the throttle every 10 or so seconds?â

Fault finding is always a process of elimination, and you've taken the petcock out of the equation, so.... your down to just the carbs. Just checking that you have blocked off the vacuum hose? I'm assuming that you have, you just didn't mention it.

I had a similar problem with the bike idling and then slowing and stalling while sitting at the traffic lights (I had rejetted the bike for a single pod on the back of the front airbox/plenum chamber and the pilot mixture was the last piece of the puzzle). The fuel screws were set too rich. leaning them out fixed the problem and drastically improved roll-on carburation from a closed throttle when cornering.

I found the following video very helpful. I've used various methods to set the fuel screws and 'blip and clean return to idle' method is now my go to.

https://www.youtube.com/watch?v=q9A2TL9RvwQ

[longranger44]

Fault finding is always a process of elimination, and you've taken the petcock out of the equation, so.... your down to just the carbs. Just checking that you have blocked off the vacuum hose? I'm assuming that you have, you just didn't mention it.

I had a similar problem with the bike idling and then slowing and stalling while sitting at the traffic lights (I had rejetted the bike for a single pod on the back of the front airbox/plenum chamber and the pilot mixture was the last piece of the puzzle). The fuel screws were set too rich. leaning them out fixed the problem and drastically improved roll-on carburation from a closed throttle when cornering.

I found the following video very helpful. I've used various methods to set the fuel screws and 'blip and clean return to idle' method is now my go to.

https://www.youtube.com/watch?v=q9A2TL9RvwQ

Thanks for the reply, I've kept mine with the stock airboxes and didn't change any settings on the carb jetting. All that is past my pay grade, eventually I might go to pods but for now I just want it to run in its factory configuration.

[longranger44]

Well good news, it would appear that the bike is fixed! I was doing some research and a guy on a Yamaha forum mentioned how sometimes gas will leak past the rings and into the crankcase from leaky carbs, and will run fine at idle, then once the engine gets hot that gas in the crankcase will vaporize and go past the rings the other way and cause it to run rich and stall. I had checked the sight glass level a while back and it didn't seem to have gone up any, but yesterday I noticed when I pulled the filler cap I could smell gas bigtime. So I drained it and it was definitely diluted. Not nearly as thick as normal. So I changed the oil and filter and voila! No more stalling. I let it idle for 20 minutes with no issues then rode it up to the corner station and filled up. No issues at all even when stopped at lights. Time will tell whether it's truly fixed or not but I'm pretty optimistic because of how consistent the stalling issue was, I'm going to go on a longer ride tonight and see how it does. I'm going to change the oil again just to be thorough and make sure it's all flushed out. Hopefully I didn't cause any damage from 20+ minutes of idling with gas diluted oil.

Anyway thanks to everyone who replied and helped me rule out other possible causes, you guys are great!

[rphillips]

Hoping that's got your running problem fixed. If gas is getting past the rings, into the oil, you've got a pet cock problem. That's exactly what that vacuum pet cock is supposed to keep from happening.... Just say'in, I've had gas in the crankcase twice, but did not cause anything near what you've described.

[longranger44]

Hoping that's got your running problem fixed. If gas is getting past the rings, into the oil, you've got a pet cock problem. That's exactly what that vacuum pet cock is supposed to keep from happening.... Just say'in, I've had gas in the crankcase twice, but did not cause anything near what you've described.

Well the gas that got into the crankcase was from before I had the petcock rebuilt and before I did the new float valves and orings. As far as I can tell I'm not getting any gas leakage since I did the float valves. With properly functioning float valves the bowl shouldn't overflow even if the petcock is slowly seeping gas, correct? Or am I wrong?
You mentioned that the guy who did the petcock maybe didn't polish where the plunger seats against, is that something I could do myself? I'm not exactly sure what part you're referring to inside the petcock.
​

[rphillips]

Correct, you got to have at least 1 needle and seat leaking "and" a leaking pet cock to get enough gas into oil to even notice. The reason for the (newer than 1977 auto petcocks) was how hard it was to keep all four needle and seats sealing properly and folks not remembering to turn fuel off after every ride. For me polishing the seat in the pet cock (with Q-tip or pencil eraser) and slightly stretching the spring for just a bit more pressure has worked good...I'm not recommending anything, just telling what experiences are.

[longranger44]

Correct, you got to have at least 1 needle and seat leaking "and" a leaking pet cock to get enough gas into oil to even notice. The reason for the (newer than 1977 auto petcocks) was how hard it was to keep all four needle and seats sealing properly and folks not remembering to turn fuel off after every ride. For me polishing the seat in the pet cock (with Q-tip or pencil eraser) and slightly stretching the spring for just a bit more pressure has worked good...I'm not recommending anything, just telling what experiences are.

Gotcha, I also heard that it was to stop fuel from flowing in case of an accident, kind of like an inertia switch in a car idea. Sounds like I'll have to pull out the petcock and try to get it to seal better by polishing like you said.

I've never owned anything with a vacuum operated petcock before, just on/off ones. Just how finicky are they even when properly polished and sealed? Even if they are working well are they prone to start leaking randomly after a year or two? Has anyone added a second simple on/off inline valve in the line downstream of the petcock? Obviously I'd have to remember to turn it on before riding but I guess I'm old school and like the idea of being able to turn off gas flow mechanically just in case the float valves start to get tired and the petcock decides to leak. Any reason not to do this besides it looking a bit redneck?

[Rijko]

i have installed an electronic fuel valve on several bikes ao my Kawa GTR1000, which has no overflow tubes and is known for hydrolock.
Around 15$ off Aliexpress, hooked it up to a switched 12v ... Bob's your uncle.
They are not very big and my buddy mounted one on his GT750 as precaution.
Won't protect you if the petcock leaks into the vacuum hose but adds extra safety.

[rphillips]

Well, when vacuum to pet cock stops, fuel should shut off. If bike laying on side still running, still got vacuum pet cock is still open. I've heard Pingle makes a manual pet cock that fits GS's. Not sure if "ON" and" OFF, or "ON", "OFF", and "RES"... Just me, the OEM work well with little problems. Usually last for yrs. My opinion when you get yours working properly you'll be good to go. When you see the inside you'll see how stupidly simple they are. Don't know about a red neck lawn mower, in-line shut off, may need to raise the tank to reach it but should work as long as you don't forget to turn it off.... Sounds like a good thing rijko. Remembering back the old late 70's and early 80's Kawasaki KZ1300 6 cyl. came with elect. shut off's. Their problem was they mounted the shut off too low, down on the crankcase, you'd run out of gas when you still had about 3/4 gal. in RES.

[tom203]

”Sounds like I'll have to pull out the petcock and try to get it to seal better by polishing like you said.“

pull it out and get new one and find something else to polish

[rphillips]

Decisions, decisions. Also there's an "O" ring on a plunger that seals to the seat, check that "O" ring for any defects.

[KiwiAlfa156]

Well good news, it would appear that the bike is fixed! I was doing some research and a guy on a Yamaha forum mentioned how sometimes gas will leak past the rings and into the crankcase from leaky carbs, and will run fine at idle, then once the engine gets hot that gas in the crankcase will vaporize and go past the rings the other way and cause it to run rich and stall. .... I'm going to change the oil again just to be thorough and make sure it's all flushed out. Hopefully I didn't cause any damage from 20+ minutes of idling with gas diluted oil.

Anyway thanks to everyone who replied and helped me rule out other possible causes, you guys are great!

Well that makes sense!

I wouldn't worry too much about engine damage. Fuel dilution lowers the viscosity, but at idle its unlikely you wouldn't have been putting enough load on the oil film to destroy the boundary layers and thus the lubrication and allow metal on metal contact.

Plus the solvent activity of the fuel probably acted as a half-decent engine flush. If it sounds like it did before when running, just change the oil and filter, make sure the carbs aren't leaking and keep riding it.

[chuck hahn]

Now you need to be 100 percent sure you hae a properly operating petcock