Dropping onto 1 cyl.

[darkember]

have put a spare old plug in the toolkit and if it does it again I will be able to check

Is this an intermittent problem then. One more thing you my want to check is to see if the ECU is all good and hasn't got moisture around the wires.

(:-})

Yes intermittent, did it once for 10 miles and then was fine for the next 300, and still good today. It got progressively worse like running out of petrol, but I struggle to understand why only one cyl effected.

This does sound very much like a foreign body got lodged in the rear carb for a short period of time & caused a fuel starvation issue. Still will be interesting in finding out the root cause

[VTRDark]

This does sound very much like a foreign body got lodged in the rear carb for a short period of time

Bloody immigrants get everywhere.

(:-})

[Hairy biker]

[Veturinkuljettaja]

I was 600km away from home last week, and I suddenly lost 1 cylinder completely. At first I thought, that it is the front spark plug boot was getting moisture in as it was raining slightly. After quick inspection at the side of the road I realized that it was the back cylinder that wasn't firing... Rain + your lady on the pillion seat + technical problems = . So I just continued riding to get to a better place to check things out. Soon after this the bike started working normally, but you could feel that the bike is not quite smooth all the time.

At the next service station I took the seat off trying to figure out what was the problem. I discovered that the positive battery terminal was not properly tightened . Connected yes, but quite poorly as you could easily move the ring terminal. I tightened everything up and haven' t had a problem since.

[geodude]

I discovered that the positive battery terminal was not properly tightened . Connected yes, but quite poorly as you could easily move the ring terminal. I tightened everything up and haven' t had a problem since.

I think the same happened to benny on a derbyshire ride out on his SP

[VTRDark]

Interesting and defiantly worth checking but strange how it only affects the one cylinder, and why the rear and not the front.

IIRC Benny's was shorting on the frame.

(:-})

[AMCQ46]

Yes I checked the battery terminals as I could remember Benny's problems from the last run

[Miztaziggy]

It's all working fine though still?

If so, the fact that it now runs better than it ever did suggests that whatever the problem was, it's somehow fixed itself, whether it was something blocking up the fuel to the carbs or what.

Maybe fit a fuel filter and see if that stops it reoccurring

[chric]

Old bikes have old technology pipe lines don't they?
I know older triumphs suffer from it and late 90 most lines where changed so millers oil man told me.as
It striped somet out of them and caused issues with the carbs going tits up like it did on dads bike new lines and an inline filter and it ran a treat after.
Or I could be just talking shite

[8541Hawk]

To me it sounds like vacuum lock as you said you filled it then let it sit.

I would check the tank vent line to make sure there are no low spots or odd bends.
If it happens again open the fill cap and you should hear the vacuum break if this is the problem.

The coils are easy to check if you have the sticks fitted. Just swap them front to back and see if the problem follows the coil.

As for why you would loose the rear cylinder first if you have vacuum issues.
The petcock isn't closing completely but only supplying a small amount of fuel.
The rear carb, usually being set richer, then runs out of fuel first.

The bike can keep running as the low flow is just enough to keep the main jet covered in the front carb.

Or the float\needle could have gotten stuck somehow.

Check the lines, maybe run some fuel system cleaner and not really worry too much about it unless it happens again.

[AMCQ46]

My current theory is this.

That the tank was air-locked [it is reported to happen if you over fill them, but has never happened to me in 10 yrs] as I had just filled the bike to the brim then left it sitting in the baking sun for 30 mins while we filled our faces. Then 5 miles up the road is started to lose power like it was running out of petrol. We know it was the rear pot that was dead as the front exhaust pipe was hot, the rear was cold and I could unplug the rear coil with no impact on how the engine was running
I now suspect the petrol tank vent was blocked by the petrol expanding in the tank and the front carb, being slightly lower than the rear carb, was still getting some petrol into the float bowl but the rear was dry.

Well that’s the theory but I will need to wait to see if it happens again and this time I have to remember to open the filler cap to see if it is vacuum locked.

[neil]

Did you check the Fuse, use a sat nav lead to try and bypass the fault, have steam coming out of bike and maybe your ears...........oh no that was a differant breakdown I read about somewhere recently

[AMCQ46]

I am getting a reputation for breakdowns I plan to thrash the bike with a branch of a tree later to show it whos boss

[Kev L]

Oooooooooh, get you with the sarcasm!!!

[darkember]

Possibly a foreign body got into the carb & slowly worked its way out. Or, even with the hotter temps could a temporary carb icing occur especially if you are giving it gob fulls??