Coil Ignition Timing

[AJSingleDave18]

Hi.

I have had an 1960 AJS M18 for a few years and for most of the time its been a easy starter with very occasionally a faint starter kick back. But resonantly its started to kick back with a vengeance. I ended up with a damaged ankle and crippled for weeks. I’ve checked the ignition timing whilst stationary and this seem correct. The advance mechanism is free and seems to be working correctly. Once running the bike performs really well, so I don’t think the timing is way out.

I am now nervous when starting the bike. I have been closely following a starting procedure to avoid starting my kick in front of, or near, the ignition position, but as the engine spins to the next ignition point it kicks back with a cloud of smoke coming from the carburettor air filter.

I’m wandering if this is due to changing to E10 petrol. Has anyone experimented with adjusting the ignition timing to optimise it for E10 petrol. E5 is not easily obtained locally.

[Greybeard]

As the owner of a 1961 G80 for the last 30 years I can tell you its nowt to do with the petrol. Mine runs no differently with E10 and 99% of the time fires first kick. The only time i experienced what you describe was after one winter layup the AR mech was sticking. It was cured with a a bit of grease on the spindle and a new set of AR springs from the club.

Steve

[AJSingleDave18]

Thank you Steve for your prompt reply. I cannot live with the bike it as it stands, and I want to use it to ride to the International Rally in Germany in a couple months time. I cannot risk being on the side of the road in the middle of nowhere in central Germany with a busted ankle, so I will take your advice and strip the A/R mechanism. Then remove the chain-case, fit a pointer adjacent to the alternator rotor and use a strobe on it to see exactly what is happening. When I last had the mechanism apart I remember looking at the springs an thinking they were slightly worn, giving a little looseness of the weights, so I manipulated the ends of the springs to add a little tension. Perhaps that is no longer enough, so new springs are required as you stated.

When I have done this, and I am confident the timing is accurately set up to the book I will see how it goes. If there is still a problem I will then, by trial and error, try various different ignition timings to find an optimum. Should this be markedly different to the book I will add it to this thread to let everyone know. I have never been a fanatic on sticking to the book’s stated timings as these are based on an average engine, the fuel, oil and driving conditions of the 1950s. Things have changed a lot since then so the current optimum timing may not be anywhere near the book setting.

The other thing I did just prior to the kicking problem starting is to replace the single-phase alternator with a three-phase version. I have now been considering whether the larger low speed electrical pulses coming from the new alternator are also pre-triggering the electronic ignition at starting speed.

David.

[Reynard24]

If it’s kicking back it could be over-advancing. If you remove the A/R mechanism check that the pins that limit the travel of the bob weights have not excessively worn. You can only see this from the back of the A/R plate. If the pins have worn with a flat on the side it will allow the weights to move too far within their limiting apertures and thus over advance the timing.
If this is the case the bob weights are available from the distributor doctor who advertises in old bike mart.

[AJSingleDave18]

I have now checked and reset my ignition timing.

First I visually inspected the points and the advance mechanism. The advance assembly moved very freely axially on its shaft when the bolt was loosened and there was just a little axial free movement when the bolt was tightened. I was unable to rotate the cam by hand as it was firmly registered by the springs, but the cam did move when the advance weight were forced out with screwdrivers. Conclusion was the mechanism and springs were fine.

I removed the chaincase with the alternator and marked indications on the rotor at 20 and 40 degrees. Then checked the current static ignition setting using a multimeter across the points. I was stunned to find it at only 13 degrees BTDC regarded. Due to the kickbacks I was expecting something like 50 degrees BTDC. The book says 19 degrees retarded and 39 degrees fully advanced.

I adjusted static the timing to the book retarded setting at 19 degrees; this was so I had a specified datum for my kickback investigations. Then started the engine with a strobe connected. At tickover it was showing 35 degrees BTDC. Completely stunned, I immediately stopped the engine, re-checked/measured my rotor calculations and markings, and then looked at the rotor to visualise where roughly 45 degrees would be. All checked out so I was satisfied my markings were accurate.

I restarted the engine. Yes still 35 degrees. So whilst the engine was still running I retarded the ignition to 19 degrees, and then tightened the contact plate screws. But every time I tighten the screws I failed to get the timing to 19 degrees. It was either 18 or 22 degrees. I gave up at 18 degrees.

It still kicks back but thankfully these are not so great and I have rode over a hundred miles on it. The engine is smoother with no noticeable change in performance.

Another train of thought is that this winter life got in the way of riding and I didn’t use the bike for five months so could the fuel be possibly stale.

[clive]

not sure stale petrol would cause the ignition to be retarded! If it still kicks back I am not sure you have found the problem.