The prewar manuals list 7/32" BTDC for ignition on full advance. Then the WD manual, for the same engine, lists 7/16" BTDC. The 7/32 must be a mis-type.
Anyway last weekend I did some tests. First: set at TDC of full retard. I did not run it; but on full advance the setting would have been perhaps an inch or more. So the lever was pulled back maybe not more than half way to obtain 7/16" - so there wasn't much retard left.
So then I set it so the 7/16" is reached with another 1/4" or so on the circle on the lever top. Marked it with a sharp paint line.
Now to test. Yes: 7/16" is fine. But I was hoping for maybe some further benefit with a touch more advance since I have had the feeling it is a bit retarded. And I think it does benefit a little bit but not very much.
Other posts here suggest 1/2" and I think that's where I shall set it if I bother to alter it again. At present it does not allow me to retard it enough to get the ultra-slow tickover I could get when 7/16" was as far as the lever would pull it.
So: next weekend it's going to go to 1/2" with maybe another replacement paint line on 7/16" just really for interest.
But it's clearly not all that sensitive (as we mostly already know) - but if it is retarded back to 7/32" it turns into a slug! I wonder how many owners put up with the 7/32" and don't know what they are missing?
Aug 4, 2017 - 3:05PM
Re: Ignition timing experiments
Hi David, I've done a similar thing over the years and tried different timings. My mag has been converted to slack wire advance so I can only retard it on the lever. I am now back to 7/16ths timing and stating again. I noticed the bike was sluggish and suspected it was retarded and on inspection it was. I've also noticed I've had to tighten my mag chain a few times. This is what is retarding the ignition. As the chain stretches the timing retards. I am now going to fit a new chain and start again. The chain has done about 1500 miles so not many miles for it to stretch like that.
It's stayed where I left it. So I normally run it on my marked line at 7/16 or just a tiny bit forward towards 1/2". What I should do next (maybe this weekend since my wife is out...) is to carry an infrared thermometer and measure the effect on temperature. My pipes are VERY blue.
Last year I took a Maplin radiant heat thermometer on a run.
When I stopped, it measured 160C on the barrel opposite to the exhaust, and 220C close to the exhaust. No wonder that they say side valve engines can go egg shaped when hot! Timing would have been 7/16inch. This was in a car park after a long hill climb (probably at Newlands Corner but I can't remember now). It's not easy to do two trials under identical conditions...
I've no idea about chain stretch. I use rear chain spray lube on mine and it's stayed there for the 2000-odd miles it's done since I last re-sprayed it and timing hasn't moved a bit.
Incidentally - check Simon Grigson's 'Norton Singles' site for an article on tuning side valves for speed!
On 'tuning' - the main reason I don't run flat out on a good enough road is mostly fear (although I like to call it "mechanical sympathy"). I assume that since the performance improvements relate to improving gas flow, they aren't worth doing unless you are already running on full bore and are not satisfied that you are doing enough damage to your bike! Which is why the cheapest and probably most effective tuning device that I have is a set of ear plugs.
Having said that - encouraging it to run cooler has to be a good thing. I'm leaving well alone. No gas flowing anyway.