Two pot good, one pot bad (’82 T3)

I’m looking for some pointers whilst providing very little evidence to go on. The story goes like this.

A few years back I took a trip up to the Scottish rally and back from my base in Essex. On the run in to Scotch Corner coming home I was giving the bike a right good thraping. In the last few miles as I approached the A1 the bike started to drop a cylinder and in the end I limped into the services there on one cylinder. I swapped the plugs there as that was about all I could do, and normal service was resumed for the rest of the ride home – though I took it easy. When I got home I replaced the coils with new and all remained good.

This last weekend I was back in Scotland. Having endured rain on and off, after a period of running in traffic around Edinburgh the bike started getting snotty on one cylinder again. I pulled over and discussed with a couple of the chaps with me – one of them thought he could smell petrol but the carbs weren’t flooding. I didn’t shut the motor down and on setting off again all was well. Two days later, limping into Fort William with a deflating front tyre, low speed, low gear, highish revs, in the rain; it started doing it again.

The bike sat out in rain all night, then got vanned down to Ayr the following day. The day after it started and ran fine, and in fact got me back home all OK – including a non-stop 240 mile run from Scotch Corner to my house with no issues at all.

So what gives?

The bike is running std 30mm carbs with pod filters. Newtronics ign of unknown age. Do I shrug my shoulders and worry not (not like me) or where to start looking? I’ve owned the bike for some years now and have changed nothing else recently.

Have you checked the HT leads?

I’ve done nothing yet, though the leads were replaced with the coils. From FB suggestions it sounds like I need to make a full check of wiring and connectors, but there is a finger of suspicion pointing at that Newtronic system. I have a points plate I picked up somewhere that could be going back on.

As a complete aside whilst I picked up one response here (thanks Chris), I got 33 on my posting on the club FB page in the same time frame. Though admittedly two of them were the ‘well don’t take the bike to Scotland then’ variety.

The bike will now mostly be parked up for winter now, SORN from the end of the month, so will get a top to bottom going through with full service before the new riding season next year.

(Riding Season - I hear you cry … yes, most of my bikes I won’t put on the salt)

I would suggest you start with the earth lead from your electronic ignition unit. I had an intermittent problem with one of my bikes which I eventually traced to this wire. The fitting instructions suggest that this goes directly to the battery ( I suspect you know this already ). As I say, it was only intermittent but I twigged that the problem only occurred when I was caning the bike, and it was the vibration that caused the bad connection.
However, I’m not sure if this will apply to just one cylinder of a twin.

This is a good call, bad earths can be the cause of a lot of issues. On my Tonti I have run additional earth wires between earth points on the frame, engine and gearbox as well as the headlamp shell, idiot lights, coils etc., as I had the frame powder coated and didn’t want to start scraping off too much paint. I am not suggesting that you do the same but to remove and clean the earth wires is a good annual or bi-annual service routine.

Thanks for the thoughts chums. The bike is pretty much parked up for the winter now - in fact I’ll be SORNing Blue at the end of the month (another year before that goes Historic).

I’m always pretty precious about earth straps but will be checking over during the winter service regimen. I’m thinking that the system is still using the mechanical advance and as I have a points plate with all the required gubbins I bought from someone converting the other way I might look at retro fitting that.

Problem with an issue like this is that you can never be sure you’ve nailed it. I replaced the coils last time I had something similar a few years back. Is this still the same issue? How can we know? Bike ran faultlessly non-stop the 240 miles home from Scotch Corner so I guess I’m still chasing shadows.