Backfire

[Steveshipley]

Hi, one of my engines is playing up a bit. Starts and runs well but occasionally backfires. I can't pin it down to anything specific though. I changed the cdi, and also for other reasons swapped a 26mm jetex for a 26mm delorto some time ago, but I'm still getting the backfire. It's an early (2005 ish) mugello 186, not done a huge mileage and recently replaced rings.
Any ideas?
Cheers steve

[Daggs]

The only time I've had that issue. It WAS the CDi !!

[drunkmunkey6969]

Backfire is nearly always electrical. If CDI hasn’t cured it, you are going to have to investigate the other items. Pick the low hanging fruit first, spark plug, ht cap etc, but ultimately...it’ll probably be a pickup/firing problem.


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[paulnobodyimportant]

In my case, did Kelso this year and had great difficulty in starting. Lots of backfiring, bump starting then it would fire up, blew out smoke, but ok as revs rised. Changed CDI, plugs and checked new set of reeds. Next job was to check timing. That's when I found that the crank was twisted and running elliptical. This had caused the flywheel to wear down the contacts on the black trigger box. All sounds a bit extreme, but that was the cause of my backfiring. But as others have said, it will be a problem on the ignition circuit. Good luck.

[holty]

i would guess at pick up or low tension coil, might be worth converting to one of anthony tambs external pick ups, a good upgrade.

[Steveshipley]

I've got one of Anthony Tambs stators spare so I'm just going to try swapping the whole stator.

Many thanks chaps.

[Adam_Winstone]

One of the first things to check is whether the woodruff key has sheared, which allows the timing to go out, hence the misfire.

Adam

[mick1]

Electrics would be my first port of call but don't rule out a fuel issue. My mate's Avanti always gives a little backfire before going onto reserve.

[psychedelicropcircle]

Low tension coil 99- 100

[Adam_Winstone]

^... that's not good but reasonable for a pickup but for an LT coil that is bin time!