69 750 backfiring

Was running good, no issues than suddenly started backfiring. I mean very loud popping at the mufflers. I have a mikuni carb, pulled it off and it is clean and seems fine. The plugs are black with carbon deposits. I think I have it narrowed down to the boyer stator/trigger plate (NT1a) which seems to have some kind of epoxy coating over the screw terminals and the coils. The coating on the screw terminal block is coming off. I checked the wires and tightened up the screws, however it is now hard to start and backfires like crazy when i do get it started.
I'm thinking of ordering a new boyer stator plate or maybe switching to a pazon sure fire. Anyways, just thought I would double check here and see if I'm on the right track?

Check your pilot jet is clear, you will need to get a correctly sized drill to clear it out properly, for a 25 Amal jet the drill size is 16 thou, not sure what it is for a Mikuni but it will be close.

It is quite likely to be the two wires soldered to the trigger plate. Vibration causes them to fracture an inch or so from where they solder to the plate but the insulation remains intact so all looks OK, but isn't. The bike will start perfectly easily but then immediately start running really badly the moment you touch the throttle. This happened to me 10pm one night , the bike was backfiring like crazy and had a top speed of about 30 miles per hour but I limped on. I managed 15 miles like that and then three miles from home I had a puncture - great...... I have drilled the plate and fitted two small bolts through the solder connections on the trigger plate, replaced the last 6 inches of wire and put ring terminals on the wires. I have only done about 8,000 miles since but haven't had the problem re-occur (yet!).

CA

I agree with the last post: check the two wires just before they attach to the Boyer stator plate (trigger plate). The copper braid slowly fractures and the bike will suddenly start running very badly. Not easy to detect, as the insulation stills look fine. You have to tug hard on the wire to see if it is still intact. On my bike the wire pulled apart about 3/4" from the plate.

Stephen Hill

Make sure your battery is ok, they can go bad suddenly, and wreak havoc with the timing.
Mike B

It could be as simple as the motor timing has changed due to the boyer stator plate moving over time, strobe light time

Yes check the wires and the fuse and the battery age/health.

Thank for all the great info. Hopefully I will get a chance to check everything tonight. Will update again soon.
Cheers!

Ok so it was a broken wire on the stator/trigger plate and a fouled plug. Back in action! Thanks for the assistance!