Curvy firing on one cylinder? How can you tell?

[jamesymurray]

Finally got round to changing the sparkies today.
When I took the rear HT lead off, there was a bit of oil around it, ditto for the spark plug, although only around the threads, not the electrode.
Front plug was fine.

Then noticed that the exhaust coming from the rear cylinder was only warm (hot but not too hot to touch for a prolonged period) whereas the front was as expected, and boiling hot.

Fired the bike up, but it seems to be running normally. Idle steady at 1k, not lumpy on revving.

Removed rear HT lead from the plug and bike fires up, but runs as describe above.

Removed front HT from plug and bike will not start.

Checked rear HT lead with plug and can see it sparking away when the engine is running.

I would have thought that I should be able to start the bike up with only the rear cylinder like I can with just the front?

[jambo]

There may be a few different things going on here.

The bike should be able to run on 1 cylinder, though it'll generally run at lower rpm and may need some throttle to stop it stalling. The electrics may not be the issue, however.

If there is an issue with the fuel system (way out of balance, air leak, blocked pilot jet etc) you may find at very small throttle openings one cylinder is working properly and the other is not getting correct fuel/air mix. This can mean that at full throttle at high revs both cylinders are working but at idle one cylinder is doing the majority of the work. When the spark is cut from the cylinder that's working well, the one that's not putting much in at idle can't keep the motor going. Unfortunately these things are not on/off in terms of working/not working.

So, aside from the spark test which suggests that at idle, both cylinders are getting a spark, and the implication that both old plugs were a similar colour so hopefully not running massively rich/lean on one cylinder, how does it run? What's the service schedule/history like? How long have you owned it etc. The devil's in the detail.

Jambo

[jamesymurray]

It seems to run fine, as it always has.
I think my main concern really is the oil around the rear spark plug.

I've had it around 2 years now, during which time I've done the usual maintenance (regular oil/filter change, filters, spark plugs) but not had the carbs cleaned or balanced.

Previous owner to me was similarly a home tinkerer.

[Redmist]

.

[jamesymurray]

Just been on a 20 mile ride. Still seems to ride as per normal. However the rear exhaust header was definitely not as hot as the front. You can touch it for a few seconds before it starts to burn.

[jamesymurray]

Problem solved, and it's a rather embarrassing story to boot.

Jambo mentioned fuelling, and I remember when I bought it (from a friend of a friend) the day I tried it there had been a fuel leak from the hoses feeding the carbs. Before I tested it, he replaced the perished hoses. Out I went, first big bike 'n all. Liked it, bought it, and have had it for the last 2.5 years.

Lifted the airbox off just now, and noticed that the hose feeding the rear cylinder had a kink in it and was bent around 60 degrees.
Replaced all three hoses from the t-piece.


Took it out, and rode it as I normally would, and nearly wheelied and binned it!
Looks like it has been running on 1.5 cylinders since day one.
As it was my first bike, I had nothing to compare it to, and just assumed that was what it was like!
I feel very silly now.

Better late than never though :)

Cheers Jambo for pointing me in the right direction

[jambo]

Good news, and glad the problem was a simple one.

Think of all the money people spend to get a few extra HP, and your afternoon has been very cost effective :)

Enjoy the bike, and try not to get caught out doing anything too silly :)

Jambo

[650]

Problem solved, and it's a rather embarrassing story to boot.

Jambo mentioned fuelling, and I remember when I bought it (from a friend of a friend) the day I tried it there had been a fuel leak from the hoses feeding the carbs. Before I tested it, he replaced the perished hoses. Out I went, first big bike 'n all. Liked it, bought it, and have had it for the last 2.5 years.

Lifted the airbox off just now, and noticed that the hose feeding the rear cylinder had a kink in it and was bent around 60 degrees.
Replaced all three hoses from the t-piece.


Took it out, and rode it as I normally would, and nearly wheelied and binned it!
Looks like it has been running on 1.5 cylinders since day one.
As it was my first bike, I had nothing to compare it to, and just assumed that was what it was like!
I feel very silly now.

Better late than never though :)

Cheers Jambo for pointing me in the right direction


Still...you cracked a wheelie

[jamesymurray]

Every cloud...