SFC 1000 misfiring/popping/backfiring

Keep us updated, please, about what you find. Maybe it was a corelation of different bad connections, but if this does not work out as the solution, I would consider new ignition coils or at least new coil wires (the ones going to the spark plugs). I recently learned that even on the original red ones, they can be replaced by removing the sealing glue (where they are pluged into the coils). Worth a try I would say and cheaper than replacing the coils in the first instance.
 
Rob7 said:
So far, found a dodgy fuse (replaced), a number of loose connections around the coils, reseated all earths around battery and coils and blew out some dust under the timing cover.
Click to expand...

Any of those could have been causing the problem. Let's hope you've cured it.
 
1st ensure the valve clearances are to spec and your static compression is within means, the electrical point or DMC spark are on at the degree you want respective to the stroke; lastly, the carbs are clean with a number jets on hand to test.

If that don't work your probably looking at a scrubbed Cylinder: Burnt Valve, Broken ring, broken piston or blown head gasket due to age.

The last thing you want is a melted piston - Causes all sorts of secondary damage including the transmission ='s complete stripe down , inspection and rebuild. What's really neat about Breganzie mills you can rebuild them on your Wife's kitchen table - Good luck with your marriage.
 
I went through a similar, frustrating episode with my 3CL. Initially after fitting a Sasche system I bought from another member I had a stutter at about 4500rpm. Thinking it was carb related, I stripped and cleaned etc. with no improvement. Valves OK, manifolds OK, Coils new. I had rewired the pickups during restoration and they checked out resistance wise. Bypassing the ign. switch and kill switch produced no change. The harness grounds and all connections checked out OK too. I suspected the problem was electrical as it felt like a fueling problem so I contacted Wolfgang about a replacement control unit and he doubted it was the issue but offered to take it and have it tested as he was going to Yurp. I did bite the bullet and bought a new unit from him and lo and behold! It pulled past 4500 to redline. The original unit supposedly tested OK but on the bike it isn't, I suspect it is vibration related and there is a poor connection in the box. Substitution of the ign. box might be the next step!
 
And another thing to check is the condition of the wire in the harness.
The reason I say that is on various Astons / Jags / Dukes of similar age .. if there is any oxidation inside the plastic,  it?s almost impossible to clean or solder again and that may be (not yet confirmed) the case on my 1200 with similar symptoms. I am changing the BTZ?s out but also the associated loom.
Measuring the pick-ups atop the frame is ~ 60 ohms and at the boxes ~ 70 ohms ? 10 ohms for a few feet of copper wire! That?s not right .. but a few more steps to go for me.
 
I had a similar misfiring with my RGS and the DMC ignition.
Close inspection revealed chafing on one of the wires running up to the optical sensor, moisture would get into the housing and cause the wire to short out on the engine case. Liquid insulation tape solved the chafing issue and gasket sealant around the cover to prevent water getting in from the top channel past the cover. I also filled a narrow slot in the bottom of the cover to allow any build up of water to escape.
 
So...been through all the wiring from the bottom up - sorted a couple possible issues - put in new plugs etc.

From 98km onwards today she started exactly the same as before - occasional pop deteriorating to being almost unrideable by 150km. Keeping the revs up does seem to help a little - but still surges and not practical on busy roads - popping and banging quite impressive.. Oddly, she always idles as per normal and at exactly the same rpm as normal - and starts without issue.

Still baffled. The only good thing is that the issue has not changed one iota so must be something else.

Could it be carbs? Running 58/108 and plugs look OK - but when it first starts it is evident that she is sensitive just off idle at low throttle openings.

R

 
So it starts fine all the time, runs reasonably and constantly for 100ks and in the next 50ks runs like crap surging and backfires. Can you stop the engine and restart at that point and continue riding without any work? If it cools down what's it like then?
 
If possible..... swap out your ignition components with known working ignition components.

Check the lengths of your fuel tap tubes also.... yes that?s right, have a known 22klm un molested Corsa that had original taps.... one tube 25mm shorter than the other  :o
 
I had a very similar problem on an early, points based, Meriden Trident. 
Fine when cold, but started missing and misbehaving when hot.  Idled fine though.   
One day, in frustration, I got fed up and revved it to 10K on the stand - it didn't miss a beat. 
Was cured by replacing the ignition coils.

Tom
 
Replace the DMC IR trigger/sensor (because that's relatively cheap to do)
If that doesn't resolve the issue, replace the DMC box
 
The symptoms you described match the ones I had as well as many of these responses here and in mine and the others, the common denominator seems be incorrect ignition timing, advance and/or insufficient spark. I made sure my ignition pickups were correct, timing was correct, and reduced the advance below 3000 RPM range. Runs great now. The carbs can be a red herring.
 
Timing doesn't suddenly go from perfect to creating a misfiring beast after 100km though. It COULD be the timing but only because the unit is malfunctioning after 100km.
 
And coming back to goodish after it cools down. That's why I asked if just stopping for a minute has any effect or does it take a couple of hours to return to okish.
 
I had a malfunctioning Witt DMC about 10 years ago. It did pretty much what you're describing. Was OK on initial start-up but began to misbehave after a while as the unit heated up. Electronic circuits can be sensitive to heat. It was sensitive to excessive supply voltage too. When it starter to misbehave, switching the headlight on (to reduce system voltage) would suddenly clear the fault. I described the symptoms to Uwe Witt at the time and he sent me a little voltage limiter to put in the power supply to the unit. It set the supply voltage at about 10V if I recall. That kept it going for about another year but the unit deteriorated further and eventually wouldn't even function properly at 10V. I replaced it with an Ignitech system.

 
Thanks for the comments. Yes, she starts and runs fine the day after and repeats the effects. I am doubtful to be honest it is coils as all three pots feel like they stop and restart - not just one. This feels more like the DMC is playing up to me. I have played around with various curves but doesnt change the problem. Plugs are a little dark when cold but likely from pottering in traffic for the last 10km to home.

Is the Ignitech a direct change out for the DMC?

R
 
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