Engine keeps dying on highway?

[Redshirt]

On my way home last night from a friends house (on a particularly dark stretch of highway) my engine stopped several times.
The first time I inspected the various lines on my carbs (thinking it was a fuel line issue) I noticed the vaccuum line from petcock popped off.
Put it back on and it started reluctantly.
only a few miles down the road, again the engine sputtered and died. Plenty of fuel, no pinches or unattached lines.
I fiddled with the petcocks and put them on reserve. Tried to start and it wouldnt run.
Pulled enrichment circuit open and it reluctantly started and felt like it was missing on a cylinder (or 2), kept giving it gas and shut the circuit. Got a few miles down the road...again. Fiddled with petcocks to run position...rinse repeat.
In about 30 miles, 4 shutdowns, coasting to the edge of the road in pitch black.

The last time it got running, ran really rough for several miles and by the last few miles it felt like it was running normal again.
Each time I restarted, I smelled exhaust that was a bit off (not like raw fuel, but more like... "sooty smell" if that makes sense).

What's this sound like to you folks? I am guessing at fuel system problem.
Ive made no changes to anything as the bike has been running reliably for quite some time. Junk in the fuel tank getting in the carbs?
Thanks

[BA80]

Next time it dies try opening the gascap. Sounds to me like a clogged air vent and your pulling a vacuum on the tank.

[mack]

This may sound

a bit silly but just for fun check to see if your plugs are in nice and tight as well as popping open your gas cap.

[JasonRedbeard]

I'm assuming we're talking about the SF, since your sig has the E labeled as "dormant."

Definitely sounds like fuel starvation. Try the gas cap, and if that fails try with the petcocks in the [prime] position. Does the bike still have an octy?

[Redshirt]

still has octi. I rebuilt the octi and petcocks when I serviced the carbs. Octi seems to be working but I am in the habit of shutting the petcocks off when I park for longer than a half hour.
Yes its the 79SF.

Havent opened the cap yet.

[BA80]

I noticed the vaccuum line from petcock popped off.
Put it back on and it started reluctantly.

Hmmm.........that statement right there made me think it was the standard.
Which is it?

If it's the Special, try running it on prime. I had to do that the whole time on the last trip to The Lost Rally because the octy took a powder on the way. Still could be the gascap though

[TopCatGr58]

Hey Greg,

Yeah, as I read thru the posts I said WTF , there aren't any vacuum lines going to the petcocks on specials, they are all gravity feed, the vacuum line..should only be one, goes to the Octy. Sounds like he might have the lines plumbed incorrectly? Yep, try running on PRIME, but pop gas cap first...the little vent is easily clogged with fuel varnish/gum!

T.C.

[BA80]

That's why a was thinking vent, if one petcock went bad it wouldn't kill the engine just starve it a bit.

My octy went bad on the way to Minnesota though and it acted the same way. It would run good for 20 or 30 miles after I filled up but then would start dying every few miles. It finally got so bad it wouldn't even get up to highway speed. Switched to prime and all was good during the rally and until I got back to OK.

[Redshirt]

double post when editing. See below post.

[Redshirt]

Sorry, I was pressed for time when writing the problem and was preoccupied when describing the problem.
The vacuum line going to the OCTI popped off at the carb side.

I wasnt getting more than 5 miles at a time, each time switching the petcocks from On to Res, then On again the next time it died.
So sounds like my octi died? Ive been at a wedding all evening so I still havent gotten back to the bike.

That sucks because I rebuilt the damn octi and put new bits in it. The bike has been running flawlessly for a few thousand miles now. Just all this cropped up after the OCTI vacuum popped off and from that point forward I had trouble on the ride home.

Incidentally, that vacuum line pulses heavily when the engine is running. I mean, it looks like the suction is half-flattening the line and then flexes open to about 3/4 its diameter in rapid succession. I dont know if this is normal. It looks like it isnt normal and may be indicative of a bad octi???

[crazy steve]

...Incidentally, that vacuum line pulses heavily when the engine is running. I mean, it looks like the suction is half-flattening the line and then flexes open to about 3/4 its diameter in rapid succession. I dont know if this is normal. It looks like it isnt normal and may be indicative of a bad octi???

No, that isn't normal.... Have you checked your valve lash? If you have an intake valve that's too tight, you might be getting 'blowback' if the valve is leaking slightly. Also, make sure you're using vacuum hose for the connection between the carb and octy; it's much 'stiffer' than regular hose which can collapse under vacuum and prevent the vacuum from operating the diaphram. That could be the whole problem right there...

[Redshirt]

No, that isn't normal.... Have you checked your valve lash? If you have an intake valve that's too tight, you might be getting 'blowback' if the valve is leaking slightly. Also, make sure you're using vacuum hose for the connection between the carb and octy; it's much 'stiffer' than regular hose which can collapse under vacuum and prevent the vacuum from operating the diaphram. That could be the whole problem right there...

I bought vacuum line back when I rebuilt the carbs/octi/petcocks et al and I always thought it was a little "soft". Got it from a hardware store, it was labelled vacuum hose.

Valve lash? (insert clueless look)
I dont know if that is the case. I dread the idea that I will have to open it all back up again.

[crazy steve]

Valve lash = valve clearance.... Unlike most vehicles, the valves on these get tighter as things wear, not looser. So a tight intake valve that's not quite closing all the way can allow compressed mixture to blow back out the carb. That could account for why the line blew off in the first place. If you've never checked the valves, it might be time to do so...

[Redshirt]

I had a buddy check clearance and it was sufficient (back then). Our gauge didnt have the incredibly tiny gauge in the book, but did pass the closest size (which was bigger than book listing). I will consider opening it up all over again, BUT I will correct the vacuum line first.

Since that hose pulsed, the clamp shook loose (one of the original tension clamps)... and if its not an appropriate hose, it could have worked itself off by the constant pulsing. Am I barking up a possibility?

[DGXSER]

If it is true vacuum hose and the right size hose, you should not need any clamps to hold it on. I am betting your on the right track with that hose. Vacuum hose should look solid and keep its shape even if your valves were a little tight.

If you checked them within the last year or so, I would doubt they have changed enough to need adjusting that badly.