E: Engine Comet Ignition Timing 2018

vibrac

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VOC Member
It seems ok but it is a messy job Ben has just sent one away to the current manufacturers for a checkup he is not too far from us came back checked and sorted about £45 that's what I will do next time he has all the gear and it's not a long job like a magneto done in a week
 

Normski

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Non-VOC Member
It seems ok but it is a messy job Ben has just sent one away to the current manufacturers for a checkup he is not too far from us came back checked and sorted about £45 that's what I will do next time he has all the gear and it's not a long job like a magneto done in a week
That's good to hear, I was hoping they did a check/ recondition service but only got the answerphone yesterday, hopefully they'll call back today.
 

Chris Launders

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Last year mine started missing on one cylinder then lost that spark completely, sent it off and it was back in less than a week, one CDI unit had failed, also he found front cylinder was 5 degrees out so it needed a new back plate which was extra. This one was at least ten years old and had done over 15 k
 

Normski

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Spoke to them yesterday and have sent the unit to them. Nice people to deal with. I bought my Alton from them backalong, a fair bit cheaper than VOC spares.
 

Nigel Spaxman

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My Take on timing is that
1) The ATD is a pretty primitive device and I think the factory recommendations were a compromise to deal with what they had.
2) Many modern devices have a fixed advance curve that is a "best guess" at what the engine needs.

I have been running a 2 stage Harley setup for some 20+ years. I set it when I first installed it by an initial advance of about 34 degrees although really can't recall how I did that. I then took it for a ride. Tried to make it detonate and couldn't
Advanced it a little on the adjustable trigger plate. Still no issues.
Repeat
Repeat - Ahh funny noises when lugged hard in higher gears.
Turn back a little.

leave alone for more than 20 years...... Change the plugs once a decade, if I remember.

When it was installed I think we surmised that at higher RPM it was reaching as much as 50 deg advance... with not too much throttle, and when the throttle was wicked open it switches to a more retarded curve.

I suppose it would be more useful if I put my Herve Hamon timing disk on and actually checked to see where it all was.

As for the Flash calling for 42 I wonder if that was an adjustment in the compromise knowing that it would be revving higher generally than a street Comet at 38??

How's that for comments providing no real world use to anyone!
 

Nigel Spaxman

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VOC Member
Robert I have read various comments about your ignition system on Woolly. I have pretty much the same thing on my bike. I didn't know you had a Herve Hamon timing disk! I have a really nice strobe light that works with that ignition really well. We should find out what you have been doing for the last 20 years. I have experimented a lot over the last few years. My bike has 8:1 pistons and it is so soft that it never detonates. I have been using timings around 34 degrees full advance. I have found it can tolerate full advance at very slow speeds. I have thought of experimenting with the VOES and using a full advance timing at high vacuum of up to 45 degrees and then having it go back to 34 with less vacuum. I think that might be what yours is doing. I have the programing cable for the dyna ignition so I have been experimenting with different curves. I can strobe time my bike through the ATD hole with some marks on the nylon gear that drives the ignition.
 

Martyn Goodwin

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Non-VOC Member
The thread about Comets running hot caused me to wonder if the recommended timing might be too advanced. I would note that Richardson says the Flash should be timed at 41 degrees, while the Comet is 38 degrees. Both of these figures seem to be advanced. I would note that 3407 was timed at 38 degrees, not the higher figure. I don't know how they came to this number, but if it were done by noting the maximum torque that would have been more advanced than what a modern tuner would have selected. Most modern tuners will not advance ignition to get additional power. They are prone to saying that just because you can advance an engine and get more power that does not mean you should.

Recently, David Tompkins adjusted the timing on his Comet on the dyno. This was a reasonably stock machine, 32 mm Concentric, 9:1 piston, stock cylinder, stock head and Mk2 cam. The timing came out to 31 degrees. I don't think anyone else has done dyno work to set the timing, so I think that is a good number.

This does not mean that 34 degrees is not fine, but it may indicate that the Comet does generate some heat from advanced timing.

David
David,

Some time back I had reworked the ATD on my standard Comet (7.1:1 compression, Mk1 Cam, 30mm Concentric carb) to give an advance range of 30 degrees (34 advanced, 4 retarded). The result was very easy starting and acceptable performance.

A few days back I had cause to check the timing and in doing so I made a mistake and set it at 30 advanced, 0 retarded. First sign of my error was difficult starting - that was a bit of a downer but I decided on a quick ride anyway. I noticed when pulling away from standstill the bike seemed down on power till the revs rose a tad then all was well - well it was great, on hills where I would routinely drop down a gear the bike sailed up them in top and actually accelerated with it. On one of my frequently used long, flat and uncrowded runs the comfortable cruising speed appeared to have increased by around 10 mph.

My conclusion - seat of the pants - is that full advance of 30 BTDC give significantly more torque that the 34 I had been using. And no, no sign of the exhaust pipe getting hot or blueing.

I am now working on my spare ATD components with the aim of having just 26 degrees of advance (13 on the magneto [remember the standard 'original' ATD has 18 degrees at the magneto]) so I can revert to 4 BTDC for easy starting and 30 BTDC as max advance for performance.

I hope to have the 'new' setup in place within the next 2 weeks.

Martyn
 
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