Fuel flow problem?

[masx]

Bike was running perfectly. 1989 Suzuki Katanna 1100f. Stopped for a few days. Then would run but with misfire. Suspected spark plugs. Put in new NGK JR9Bs. Old ones were perfectly grey and good. Still wouldn't idle and without revving would just die.
Set petcock to prime. Bike started and ran fine, switched to run and it ran good around parking garage ok. Then left it, back later and same misfire. Lots of spark etc from new battery.

This is what I THINK is happening: When on PRI, the fuel flows into the carbs, and it runs great, then while running I switch petcock back to run and it runs great. BUT, I think it is running on what flowed into the carbs on prime and then it runs out and the vacuum feed doesn't keep filling the carbs. Could that be?

The gas shows under 1/4 on gauge. Could it be simply too low to maintain idle? That has never been a problem before.
I thought this was electrical before but now don't.

Any one also have info on gas cleaner stuff like Seafoam? Dare I use it? Doing any work on carbs is way above me.
Any ideas appreciated about fuel system etc.
This bike has been running like new for 31 years!

Thanks for whatever you say.

Bob

[masx]

I THINK I might have found my problem. Just a note if you had similar problems, I THINK a vacuum hose came off my petcock. This is nearly impossible to see as it is under the tank. I will prop it up tomorrow and have a look. When I look in to SEE the petcock I only see the slot to adjust it ON or PRIme and cannot see the back where the vacuum hose would attach. However there is the end of a hose in there visible, sitting loose. and I THINK it is the vacuum hose that is unattached! Will tackle it tomorrow and post it.

[Court93kat]

If the vacuum line came off the petcock, it will cause issues like that. Also, the horrible idle would be because you have a vacuum leak into carb #4. If that is the original hose that came on that bike, it might be time for a replacement. The rubber would be getting pretty stiff and brittle. You can get some vacuum line from whichever auto store you prefer and replace it. That is a part that does not have to be ordered through a motorcycle dealership.