M750 suddenly running like crap, then got better

[MongoReturns]

So, the ol' reliable 2000 M750 was sitting in traffic for a bit (new MLK memorial, #$%!) and once I started going again kept threatening to die; I had to modulate the throttle to keep it going.  This has never happened before.  It seemed to sort itself out as I went into panic mode, thinking I just need to get back across the river (Washington, DC).

I had a half a tank of gas, and the gas has been in there for awhile (month?) with lots of temp fluctuations around here.  I just topped it off.

You all think gas?  Unless I get other advice, I'm going to put some Stabil in there and stay close to home to see if it happens again.  Very disconcerting.  Fuel filter is relatively new, pump rebuilt around 500 miles ago without issues.  Spark plugs like 5 years old, but they're always perfect.

Thanks

[He Man]

is that bike carbed or injected?

if its carbed, i had a similar issue that took a lot of tracing and running around.

the bike would die only in traffic, but sort itself out when in open temps.

thought it was a vacuum petcock, but that was clear (if it fails, it tends to fail in the open position)
then i thought it was the fuel filter, so i replaced that, no joy.
then finnaly when i opened the vacuum fuel pump. the diaphragm was flimsy and not really working well. bought a genuine rebuild kit and problem went away.

the heat would make the diagram not work because it was so stretched out already.

bike only had 15,000 miles on it, but was a 99 carbed 900.

[MongoReturns]

Carbed.  I just ran it for 25 miles after I put Stabil in it, in varying speeds, it seems fine now.  I have been worried bout that vacuum petcock for awhile.

[ducpainter]

5 year old plugs?

I'd put a set in just for the practice.

[Howie]

In addition I would change the fuel filter and drain some fuel from the carb float bowls to check for contamination.

drains

Drain into a clear container.  Any water or dirt will sink to the bottom.

[MongoReturns]

Ah nuts I forgot about those.  Chances are the stabil combined with the fuel by now, but guess opening those screws wouldn't hurt.

It's never bogged down like that before.  I don't like it.  The 25 miles with the Stabil were normal, but I didn't sit in traffic for 15mins.  Ugh.

Nice pics btw, that's the cleanest old Mikuni I've ever seen!  And I should change the plugs, may help with the st-st-stuttering.