Odd behaviour - misfire?

This morning, I thought my Cali 1100 (with carbs) was running out of petrol, as it was stuttering and running on one cylinder as I rolled into work. I filled up at lunch (it was down to the last 2 litres so not exactly running out) and took it on a 20 mile run to get it warmed up. I was sure I could hear the odd bit of pinking/misfiring - under constant running rather than under load, and when I stopped, the tickover was steady but there was just the occasional ‘pop’ from the exhaust. A little revving produced a ‘pop’ on the overrun each time. Coming home tonight, and all seems fine again. Just one of those things?

fuel filter? crud in float bowl? I’ve just had fun with several times resetting tps (no threads aren’t stripped)McFuzzi2014-08-11 22:23:30

That’s what they call character.

Carb to inlet mounting rubbers split? Usually just a question of time…

Mine did that when one of the coils was starting to fail.

I guess the difficulty is the ‘vague’ nature of the problem.
In some ways a plain old ‘will not start’ is easier.
Best of luck with the fix

‘Vague’ as in hasn’t happened since. Another run again today failed to reproduce the fault. I feared that the popping might have indicated a sticking inlet valve. I don’t know why, but this seemed a logical explanation.

There you go. The Guzzi Forum Universal Mind fixed your bike whilst you slept.
Fingers crossed

Trying to imagine that, and A. I can only see it sticking open, not closed, 'cause the cam won't let it stay closed ~ unless the rocker was broken, which is possible, but then B. the piston will just whack it closed again. Which might bend the stem.   Broken rocker or bent stem, you'd know all about it.      Had a broken exhaust rocker on a BMW car once, the blow-back pressure due to the exhaust valve not opening was so violent it effectively turned the carburettor into scrap.        Edit: yes I agree it could be looking like symptoms of intermittent ignition fault. Dodgy coil winding maybe. Bad spark plug....    

Mike H2014-08-13 01:00:45

Appendix: however, popping noises especially on the over-run are usually caused by too lean running, so we’re back to possible downstream air leaks again. Or could be a bit of crud in the carb caused it to go lean for a while. How’s the floats in the carbs, any danger of fouling on the sides?

If you’ve got plastic floats like I have you may have the same issue that I had with the plastic swelling & then the floats got stuck between the pivot posts. The cure is to file a bit of the plastic away. No more popping & banging as the floats now float.

Will be cleaning those carbs out soon.

Popping on the over run is often a sign of an air leak on the exhaust to cylinder head joint, but it wouldn’t cause the other problems of poor running. Maybe getting low on fuel just stirred up some crud in the bottom of the tank. Might be an idea to drain a bit of fuel off from the tank into a glass jar and check for water and also to blow through the fuel lines when you have the carbs off incase they have been affected by ethanol.

 Old wives' tale.    Fuel is ALWAYS taken from the bottom of the tank.     I had to be told this and even then still had to think about it for a bit to realise it was true.        Although it could be true if your reserve tubes work (which mine don't) then yes there could be like a bit of a 'bilge' below the taps' take off level, so to speak. But soon as you go onto reserve, you'll get the dregs. Or not, as the taps should have filters.   

Mike H2014-08-13 22:14:54