Bike conked out on the interstate - help finding cause?

[Flyin' Low]

First, I made it to an exit ramp gas station OK, so that was nice. But I'd like some help figuring out what went wrong.

Was tooling along just fine at 65 mph (totally warmed up) and bike started to run rough, then progressively got worse. I needed to add throttle, then downshift & add more throttle, etc, until I was in 2nd at full throttle just to get over to the side of the road at 15 mph. This happened in maybe 30-60 seconds. It seemed like it was missing on 1 cylinder, then 2, then 3, and finally died when I let off the throttle when I got to the curb lane. Cranked over fine, but wouldn't restart at all. Lights bright (new battery). It wouldn't even cough, except if I gave it a ton of choke, but even just that got a couple of sputters. I noticed that one spark plug wire seemed loose, but couldn't see anything else obvious, and nothing changed after it was plugged back in.

After pushing it to the gas station I got a pickup from a co-worker, & when we came back at lunch with a truck & 3 guys to load the bike, it started fine. I stuck it in the truck anyway. One of them suggested the fuel filter, which I took out & it seems to flow OK (can't see inside & don't have another handy, though). The bike now seems to run OK, still a bit rough but it's gotten out of tune & there's a little rust hole where the exhaust pipes join up, so I'm kind of used to that.

Any help? I've noticed this symptom before (it almost feels like running out of gas) but it's only been this bad once, usually it just hesitates/surges a bit and then goes back to normal, and it always seems to be OK after letting things sit a while.

Thanks in advance.

[Flatline_Racing]

I don't know if it is applicable to your bike but the vacuum operated petcocks sometimes get nackered. Is there a 'PRI' setting on it? If so, try that and see if it makes a difference.

[Flyin' Low]

I do have that setting, and I did have it set to PRI when I restarted it, since I had disconnected the fuel line. If it happens again I'll check this, thanks. It did seem to run fine after returning it to the normal position, though.

[DanTheMan]

Get rid of the fuel filter(it isn't really required, and can starve the carbs for fuel). Make sure your vacuum line is well attached to #2 carb or your petcock won't operate properly. Sounds like classic "run out of gas" symptoms.

[ronin1166]

Agreed on the "running-out-of gas" problem profile...dropping one cylinder after another.

My guess is petcock/vacuum problem (try replacing the vacuum hose - with 'vacuum-specific' hose, NOT generic fuel hose).

If it's not a vacuum-line problem, it could well be the petcock diaphragm itself.
Or a big, nasty blockage of the petcock-screen (sticks up into the fuel tank).

.

[tkent02]

Did you check for a clogged fuel tank vent?

[Flyin' Low]

I haven't checked the tank vent or the inside screen on the petcock. Will do tonight (though the tank's almost full now...). I think the petcock hose is OK, but may be able to swap it. I know I bought some extra fuel line so if the filter's the issue I can make a longer one and connect direct.

Thanks for the suggestions.

[Skateguy50]

Did anyone mention lose the inline filter?

[ddaniels]

Mine did the same thing the first long(ish) ride I took it on. Hasn't done it since. I hate that. I considered replaceing the petcock, but not unless it does it again.

[koolaid_kid]

Certainly fuel-related, no go juice, no go. Just keep tracing it down, the culprit will turn up.
Did anyone mention lose the filter:

[Dogma]

My 850 did it a couple times, especially when the tank was getting low on fuel. A new petcock fixed it.