Help diagnose stalling bike

I'm unfortunatly not an expert on the old bike i'm riding so any thoughts are appreciated. The friend who i bought it from is my source of info/repairs but he's away right now.

83 Yamaha XJ750 MAxim. Rode all last year with no problems. Been riding for over a month this year with no problems. New spark plugs and carbs balanced last year.

Coming home the other day i noticed it felt like there was very little power while starting from a standstill. This got worse and worse with each stop to the point where i almost couldn't get the bike moving without stalling. Luckily it was only a straightaway to get home from there but travelling at 60km/h on a flat road i started slowing down. More throttle produced nothing and eventually it stalled. I pulled onto a side street. Engine would turn but would not start.

Checked the exhaust headers. One was hot. One was warm. Two were cold.

Put the gas valve to prime for 60 seconds. Set back to ON. Bike started perfectly and sounded perfect. The rest of the ride home, including starting up from 1st gear, felt 100% perfect. All 4 headers hot when i got home.

Since putting it on prime seemed to cure the problems i assumed it was a problem with the vacuum hose from carbs to fuel flow valve. Took it off and blew carb cleaner through it clear any blockage. Unfortunatly didn't actually test ahead of time if it was blocked.

Now bike starts and idles for 5 minutes perfectly. Drives up and down the street perfectly. I'm just afraid to go anywhere since i have absolutely no way of getting this thing home if it dies on me somewhere. It won't fit in the back of the corolla.

Anything else i should check? What else could it have been?

All thoughts appreciated.

 

I would rebuild your fuel petcock. It sounds like it's not operating correctly. The kits are cheap and Len has them.

 

How low were you on gas? We've all done it.

PRI will draw fuel from below the ON position as will RES but once you've run a fuel bowl or two empty PRI is best to get them refilled and the only way to do it with the engine off and leaving everything together.

You could also have a clogged or partly clogged petcock tower filter in the tank.

 

Could also be a plugged gas cap vent.

 

or a fuel filter with an air bubble. Had that last year.

 

Maybe it's a gremlin. Hopefully it's my gremlin from my bike leaving mine and going to a new one LOL JK

 

Ain't no such thing except in Bugs Bunny cartoons.

The only thing wrong with your bike is the same thing wrong with his---

Time and neglect, and the deterioration that results. Reverse it ALL and guess what? No more "gremlins."

Anything skipped over will show up disguised as a "gremlin."

 

So looks like this was a classic case of ... not sure what it's called in the motorcycling world. In computers we call it PEBKAC. Problem exists between keyboard and chair. In other words, user error.

When i pulled over after stalling I did check the gas tank and it looked like i had a decent amount. When you look in you see the right side of the tank. Well thinking back on it i was parked on a downhill slope that also angled to the right. So it looked like there was a lot more fuel in there than there actually was.

And then when i did my testing in the driveway i ended up putting it to RESERVE instead of ON which explains why i had no issues.

Long story short i ran low on gas as someone did suggest.

Thanks all.

 

Vacuum Line to Petcock ... Not Genuine Vacuum Line and collapsing.

Foreign Matter accumulating on Petcock Tower
Slipped Petcock Wafer
Clogged Petcock (Clean with Weed Whacker Line probe)
Low Fuel in Tank

 

Rick he already said it was low on gas....

Kevinck now you know how it acts when it runs out of gas. Now practice finding the RES setting while riding it so it doesn't stall in traffic.

 

Or just remember to fuel up...

But yes, I did not know how it behaves when low on gas. Now I do.