XS1100SF Running on 3 until warm

[EricHa]

What would be causing my newly acquired SF to start up on 3 cylinders, and not pick up the other hole until it's warm? Choke settings don't seem to make any difference, at least not lately as it's 90+ degrees all the time. Even running on all four it needs feels/sounds like it needs adjustment/synced. Any help is appreciated.

[DGXSER]

What does the plug look like after you start i but that one does not fire. Is it dry or wet with fuel?

Have you tried trimming a little off the end of the plug wire (unscrew cap from wire, cut back the plug wire to fresh inner wire, screw plug cap back on).

[fredintoon]

The usual suspects

What would be causing my newly acquired SF to start up on 3 cylinders, and not pick up the other hole until it's warm? Choke settings don't seem to make any difference, at least not lately as it's 90+ degrees all the time. Even running on all four it needs feels/sounds like it needs adjustment/synced. Any help is appreciated.

Hi Eric,
runs on 2, it's the ignition. Runs on 3, it's the carbs.

[EricHa]

What does the plug look like after you start i but that one does not fire. Is it dry or wet with fuel?

Have you tried trimming a little off the end of the plug wire (unscrew cap from wire, cut back the plug wire to fresh inner wire, screw plug cap back on).

Honestly I've only looked at the carbs after all 4 having been running. I will say that #2 plug cap seems loose, and may be the problem, but why only when cold and not warm? I will try your suggestion though, thanks. I'm on the fence of trying to rebuild the carbs myself, or just having Rick West do them (right the first time).

[cywelchjr]

Honestly I've only looked at the carbs after all 4 having been running. I will say that #2 plug cap seems loose, and may be the problem, but why only when cold and not warm? I will try your suggestion though, thanks. I'm on the fence of trying to rebuild the carbs myself, or just having Rick West do them (right the first time).

With heat tolerances change, even in the wire. As things heat up the wire may make just enough contact to give enough spark to work. Try the wire trim first, and if that doesn't work then look into the carbs, but temp based I'd be more expecting wire or a leaking spark plug or such. Have you tried swapping the plugs? Swapping the wires between the cylinder that's not firing and it's mate (3 for 2 and 1 for 4 etc)?

[EricHa]

I will try the wires first then. I should be replacing them anyway. 32 years it's probably time

[cywelchjr]

I will try the wires first then. I should be replacing them anyway. 32 years it's probably time

They are not actually replaceable. You actually have to perform surgery on the coils to replace the wires, and there is a real if small chance of killing your coils when you do so. This is ONE of the reason people go to aftermarket coils, because the wires on their OEM coils (which have been NLA for many years) are shot.

That said, barring rain (and sometimes heavy rain), often just cutting about 1/4" of wire off the end (enough to see clean copper at the end) and putting the end back on will many time fix the problem. Additionally the caps wear out, they really have a finite lifetime, and can be bought online and at most MC stores (I got new ones at cyclegear) for just a couple $ each. The resistor can burn out, and that could the a source of the symptom on thinking as well. Using an ohm meter, check JUST the cap, you should get 5k ohms from the screw to the clip that hooks to the plug. If it's different it's time for new ones.

[EricHa]

That's great info Cy, thanks. The plug cap on #2 is loose on the plug. A little fiddling and she fired right up on all four cylinders. This bike had all OEM parts and low miles, though it has sat for decades. I replaced the rusted out exhaust with a Jardine 4-1 using the stock airbox. I clearly need to go through the plug wires, and also find out the jetting. I've got a Motion Pro sync tool in the box, so a sync sure wouldn't hurt.

Checking the valve clearances is probably needed as well. Don't these engines use the same shims as the ones in my KZ900? Anyway, thanks to all for the info. This forum is great, and it's because of it's members helping to keep these largely forgotten beasts alive. Hail to the air cooled fours, and I'll hit the search function more.