Almost there - A question

[Incubus]

The weather was pretty nice today - mid-60s - so I took my '79 XS1100 out for a iron-out-the-wrinkles drive. I have some issues with the way it runs under 3,000 rpm, which I believe are the carb holders - or at least one carb holder - but since have very little interest in driving at less than 3,000 rpm I will worry about that later. It runs great over 3,000 and my shoulders are pretty sore.

One thing concerned me, however. I was tearing down Highway 79, really torquing it, when I had to ease off a bit because of a really inconsiderate driver who doesn't understand how we drive in Texas IN THE LEFT LANE. Anyway, I got around her and I gunned it again. My bike suddenly was running poorly. It was missing on one, maybe two cylinders. I got to a stop light and revved it a little thinking I might have to do that to keep it running. When I took off again everything was fine. It was a burner again. As I ran it home the mysterious missing happened again, this time when I wasn't torquing quite so hard. But I was forced to slow down and travel at a lower rate of speed behind a rolling roadblock that looked like a Suburban. Afterward the power was back and I had no further recurrences. I gunned it coming up my street and almost slid off the back.

When it cooled I pulled the plugs. One two and three were a nice tan. Number four was different, somewhat whiter.

I have three theories. 1. A bit of grime in my shiny clean carbs locked jammed somewhere until I eased off the throttle. 2. While messing with my hitherto perpetually leaking petcocks (healed now, apparently) I stretched the spring behind the diaphram a bit too much and leaned up the fuel flow a bit too much. 3. I set the carb floats at 25mm and that may not allow enough fuel into the carb bowls when I am seeking liftoff velocity.

Which do y'all think most likely, based on these symptoms? I'd really like to solve this once and for all.

Thanks, y'all,

Patrick

[Dragonrider]

Check the fuel tank vent too...if plugged, a vacuum prevents full fuel flow...

[Ken Talbot]

Pick-up coil wires. That will give you an intermittent loss of two cylinders like what you describe. The issue of poor running below 3000 rpm is carbs and/or synchronization.

Sorry.

[oseaghdha]

Sounds like crud getting in the carbs.
I had the same thing happen about 100 miles after I got mine up and running. Was buzzing down the 121 when it acted like it was running out of gas. I zinged it with the clutch in, and it was ok after that.
Pretty much all performance issues have been carb related, for me.

[acof911]

Pick-up coil wires

...or the pickup coil vac assy. is sticking and not moving properly.

It happened to me out of the blue one day, the old girl felt like she was running on 2 cylinders.

I thought it was the pickup coil wires too. Take off the cover and make sure the plate the pickup coils are on is not stuck and moves a bit when you rev her up.

A shot of lube fixed my problem, you may get so lucky!

good luck,
Andy

[Incubus]

OK, what I've done so far.

Replaced the pickup coil wires on one side. The bike started. I couldn't get the idle down, so when I timed it I might not have gotten it right. Figured I'd do it again after I synched the carbs.

Started synching. Got three and four together, the idle came down. I got one and two together. Then, as I was synching the pairs - they were real close - the idle dropped and the motor stopped. It won't start again. Occasionally I get a pretty cool backfire. I have spark - I even put in new plugs. I have fuel. The plugs come out smelling of gas.

The synch was getting real close when the motor stopped. Cold it be the synch that cut it off? I was suspecting timing, but unlike my points driven bikes I have no idea how to static time this bike. How can you time a non-running XS engine?

Suggestions?

Patrick

[Incubus]

Never mind. My Rainman-like simplicity is truly a wonder to behold. It truly amazes and frightens me that this same brain is telling my heart to beat and my lungs to inhale. All evidence seems to indicate that it is my brain, rather than either lung, that sucks.

She runs.

Patrick

[Ken Talbot]

Now come on, Patrick, you can't get away that easily. One minute it is running and close to being in sync, then it dies, then it runs again. You gonna come clean, or are we going to have to run a little contest to see who gueses what it was?

[Incubus]

Well, Ken, I'm back in the guessing game too. Cuz it didn't get cured. Thought it did, but now I'm wondering if synching can strangle a fuel flow.

What I did before posting was undo what I had done. That's what mean by Rainman-like simplicity. I backed the middle synching screw out a turn, which took it further from synch, and pop - it started.

I proceeded to set the synch, turned the idle down to 900, according to my stone age caliber dwell tach (which I've had since it and I were young - a long, long time)and zeroed in the timing. Ken, it was purring. It was beautiful. I swear, she winked at me.

Turned it off. Went inside and posted the "never mind" and got my helmet and gloves. Rolled her out of the garage. It was a beautiful day, about 70, no wind. I'm gonna make some wind of my own. That's why I didn't go into a lot of detail. I didn't want to waste such a gorgeous day.

I hop on, hit the starter button, and listen to it crank. And crank. And crank.

Finally, one very impressive, dead-people-awakening backfire. It was the loudest backfire any of my bikes has ever made. I thought for sure I was the victim of a very close range driveby shooting.

Then nothing. Damn.

Pulled the plugs. They're all firing and they're all bone dry, although I've been running the petcocks on prime and I can see gas in the clear lines.

Could I have cut off the fuel flow adjusting the synch?

Patrick

[John]

Are you using a remote fuel tank, is it out of fuel, or are you using the bikes tank, just have it sitting off to the side, and not have the vacuum lines attached to allow for fuel to flow to the carbs?

[Incubus]

I'm using the bike's tank, still in place, with the back end of the tank elevated to allow access to the carbs. The tank has two or three gallons in it and I have the petcocks on prime. The vacuum lines were removed from the carb holders to allow the vacuum gauges to be hooked up and then returned after I "finished".

The tank was returned to it's proper position after I finished synching and timing and everything was put together for the ride. Vacuum lines returned to their proper places. After it didn't start, I pulled the vacuum line to number two carb and there is indeed sucking going on when I crank it. It should be drawing fuel, but apparently it is not. I didn't check the other vacuum fitting to see if they also were sucking.

The only thing I am positive is sucking is my workmanship.

Patrick

[Incubus]

One other thing. I just checked and there is gas in each of the carbs.

I thought all synching does is make sure the butterflies are all the same. And the bike will not start with full choke, half choke or no choke.

I'm thinking this has got to be a problem with the timing. It looked spot on, but it seems to me my indicator arrow was a bit off. How far off would the timing have to be to keep the bike from running?

[skids]

(deleted)

[Ken Talbot]

Changing the sync has no effect on fuel flow to the carbs. Your problem still sounds electrical to me. Check out all of the wiring from the pick-up coils all the way to the ignition coils. It seems like dropping the tank back down might have dislodged a connector, or pinched and shorted out something. That sudden a death has to be electrical.

[Incubus]

I really inclined to agree, Ken. I noticed something else that may help track it down, if I could make sense of it. It could just be my desperation crafting ghosts in my mind.

I am so close. I just know it. I was, of course, much closer two day ago. I figure at some point the carbs are coming off again. Maybe that's a good thing. I can give them one more once over before I put the bike into regular service. Maybe bench synch them again. Better to do it now when I am intimately familiar with them than in a year or two when I may have forgotten something.

Digression warning: I checked the resistance on the wires from my pickup coils to the TCI to check the integrity of my repair on those wires. I get about 700 ohms across both pairs of wires and the resistance doesn't change when I rotate them.

Back on the subject: I was checking the spark yet again by grounding my number one plug to the valve cover acorn nut. I get a strong blue spark. And, when I ground the plug, the bike sounds like it's trying to start. Much moreso than when I am cranking it. There I still get only backfires. Since the plugs ground to the had, what could make the spark strong and maybe complete the circuit when I ground it to a mounting stud?

Yes, I double checked the kill switch.

I'm kind of musing out loud here. I'm deep into the pondering stage and wishing had another mind in my garage looking this beastie over. Did I mention, anywhere in this thread, that the bike was running? That actually rode it? And I was only trying to fine tune it when I killed it?

I pulled the tank and seat and I don't see any connections dislodged. I am baffled.

Patrick