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[Simon Cornell]

Having a much better day today! Not exactly sure why but got results...

Adrian, I took it back to simple, and got it in the ball-park of .8mm btdc, checked the auto-advance and it's moving freely, no rubbing. I knocked it off its taper to retard its position (relative to the distributor) slightly as I was on the limit of the breaker plate adjustment. When I'm indoors out of the elements I'll try with a timing disc from full advance.

Wheaters, thanks for the clearance valve suggestion, the inlet tappet wasn't spinning freely so I loosed a bit. I found a great use for a PPE glove thanks to Bullet Whisperer's ingenious Youtube of sealing the intake with one and checking for air leakage on compression stroke (https://www.youtube.com/watch?v=ZFuwKHYQRSo). Fine there now, but maybe it was a bit too tight before, could have made the difference without needing to reseat the valve?

Stinkwheel, I replaced the Mikcarb and it started first time without connecting throttle, it idled nicely and responded well to adjustment of throttle screw. Then put the Amal Mk1 Concentric 600 on again and it ran pretty much first time too. Maybe it's just happier with a warm engine, but starts on full choke but no need of throttle. However, the idle wanders erratically up and down the revs unaided quite a bit, and often has a weak stroke and often dies with puff/gasp. Could this be a weak spark? It is a 20 year old coil?

I noticed the seal around the exhaust pipe/engine is not good, with black exhaust residue visible. I read that mastic sealant works further down on the silencer. Maybe too hot at the head? What is the usual remedy there? Would this affect the wandering idle revs? I will try a spraying WD40 around the intake port but the join seems tight but not overly so.

Finally I seem to get my head around the auto-advance and timing principles, thanks for the discussion and I shall now try and work out what the pinking sound is, and work back from there. Once I'm off the curb-side I'll work up to a strobe light!

I can't quite put my finger on why it starts today after switching around carbs, but repeating process obviously cleared up something I overlooked - maybe the tight-ish inlet tappet. It is progress and I am not complaining. Thanks all for getting me there, great to have support! Simon

[Simon Cornell]

p.s. for any other neophytes like me out there, I found two excellent resources for working out the Amal Concentric Mk1. https://accessories.hitchcocksmotorcycl ... 4&_xt=.pdf is from our hosts and another from Norton owners https://nortonownersvic.org/wp-content/ ... ric-v2.pdf. In case helpful for others searching info.

[PeteF]

Ordinary silicone bathroom sealant is fine for the head/downpipe joint.
NOT mastic! That term covers all sorts of sealants which would not be suitable.

[stinkwheel]

You can lock the auto advance to set the timing in the fully advanced position with a little dished washer thing from our hosts. Set it at 8.5mm BTDC (easier to get the piston to stop at this point among other things).

Some points shafts have a huge amount of horizontal play on them which can intermittantly interfere with the auto-advance. If it does, you can knock the timing side iron bushing out a bit then reassemble and tap once with a small hammer to re-seat it just enough to allow rotation but prevent the sloppiness (requires removing the distributor shaft and timing side pinnion).

Bathroom silicone sealant works fine on the head too.

Wandering idle is the classic sign of an air leak so the WD40 test is probably worth a go.

If you have the Amal off again, worth checking for any bits of swarf/poor machining in the drilling between the fuel banjo and the needle valve, I've seen pictures of some awful examples. I also recall they have a gauze sock filter in here which to me seemed redundant given it is coarser than the one on the fuel tap. I removed mine.