D125 backfiring & slight loss of power

[bjhart]

Hi All

I completed the London to Brighton run at the weekend (fantastic event by the way) but on the last few miles i noticed a drop off in power plus occasion backfires... i managed to nurse it back to the finish line though. Yesterday i fitted a new plug and it started ok and seemed to rev fine, but on the way into work today same thing. I did notice the plug looks a bit rich when i changed it yesterday.

Obviously i need to go through the same old checklist (well troden path) of potential issues but can anyone point me to the best start point with this particular symptom?

List of things i plan to check/ exchange where possible
1. fuel cap breather not blocked
2. fuel tap filter not blocked
3. HT lead
4. HT cap
5. Points gap/ condition
6. Timing (what is perceived optimum on fixed timing degrees & travel please?)
7. Carb clean
8. Air filter clean
9. Condensor
10. Combined LT/ HT coil fault
11. poor connections
12. faulty kill switch (combined light/ cut out button)
13. ignition coil contact

Have i missed anything obvious?

All input greatfully received
Barry

[weeks]

I had a bout of back firing just before the Transport Café stop - Plug change and this cleared it even though I know I over egged it with the 2 stoke oil when I filled up that morning.

Id try a fresh bit of clean fuel first - Check you haven't just followed my mistake or have a bad tank of petrol (easy point to start) - Good luck

[jbcollier]

Could be coked up as well. Not as common with modern oils but it still can happen.

[bjhart]

Cheers Gents
The fuel was the same used in both my F & D on the day..... so i think its unlikely, as for being coked up its only done a few hundred miles since being rebuilt I'm leaning towards an ignition issue....loose wire, dodgy condensor or coil, hopefully i'll get a chance to have a good look at it over the weekend and start eliminating the easy things first...... i had a similar issue in the past so bought a new coil but it didnt cure it...it was the condensor, so I might be able to verify the coils assuming the spare one i have is ok... not sure if the combined LT/HT internal coils can be checked very easily???

Also can anyone confirm the ideal ignition timing and points gap for unleaded fuel I'll check that while I'm in there and adjust if neccessary.
thanks

[jbcollier]

No need to change timing for today's fuel. While today's fuel isn't available in the same high octanes as the 70s, it's still way better than anything available in the mid-50s.

[bjhart]

Finally nailed it... faulty NOS coil, new CASA one has sorted it. It is running a little rich, anyone got a spare 70 main jet it’s got a a 72 in it at the mo
Cheers