E: Engine Comet Ignition Timing 2018

Bill Thomas

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I should have also mentioned that David T is running a single plug new BT-H, so a very typical ignition. The piston was changed to a 10.5:1 and the subsequent dyno run set the ignition at 28 degrees.

Many racers run at full advance, including me, but I could not tell you that it is hard on the engine from the performance.

I avoided mentioning ATD's because I think it can be a problem with no good answer, but it is interesting to see how owners deal with it.

Bill, you are good on that 64 mph at 4000. Of course, maybe never getting to full advance is a good thing!

David
What I am saying is if you set a small spring to work midway, It will stretch in a short time and the settings will go to pot !.
I don't like ATD s, I prefer the "D" type distributor, But that also has springs, When I was running 12 to 1 s
and wanted 24 degrees, I just put a plastic tube over the shaft to stop the bob weights shutting fully, It worked well. As I have said, My Comet has Manual advance, And I have played with the lever at all speeds, But once over 2000 ish it's best left alone.
I think theses are old bikes and as a rule work well. Cheers Bill.
 

greg brillus

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Most auto advance units usually had two springs of differing tensions. The fact that these seem to advance quickly to me would suggest that at low engine speed pulling up a hill with too much advance would cause detonation. But the extra heat from detonation is very different from a retarded ignition where the flame is burning too late.
 

vibrac

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Just take the alloy end cap off the BTH and look at the small pole ends of the coils, if there is any signs of rust or similar, buff it off gently with a dremel. Just make sure the rotor arm with the magnet on it is out of the way and be careful not to pinch the wires that pass through the small cutout at the lower rear of the cap when you re-install it. This turned a Shadow from a non starter to first kick again.
"Just take the alloy end cap off the BTH" mmmm
I am faced with one off round head allen screw, off set from the center on a plain alloy surface that I expect is the cap but it does no feel like a securing screw when I turn it anti clock it does not come out nor does it return to its original tension on going clockwise is this the securing screw for the cap? or how else is it secured? as it is supposed to be nonmaintainable is there a step by step guide anywhere I can see its a little delicate its also a model BTH from the early days of production
 

vibrac

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Need photo's, not sure I remember what the earlier ones looked like.
here tis..
1530294397235.jpeg
 

BigEd

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Early versions of this single magneto have an extra part on the end cover with the BT-H logo machined in. This made it easy to locate and secure the items/wires inside and then fit the logo item to cover the hole. The Comet version didn't have this extra part because it had to be short enough to go under the magneto cover. The dome head Allen screw at the bottom right hand of your photograph holds an earth wire and a clamp for the CDI unit. It was awkward to fit things in and keep wires clear of the rotor arm. The end cap is held on by the Allen head caps screws, one of which can be seen at the top right of your photograph.
If you are going in there I suggest you go very carefully.
 

vibrac

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VOC Member
Early versions of this single magneto have an extra part on the end cover with the BT-H logo machined in. This made it easy to locate and secure the items/wires inside and then fit the logo item to cover the hole. The Comet version didn't have this extra part because it had to be short enough to go under the magneto cover. The dome head Allen screw at the bottom right hand of your photograph holds an earth wire and a clamp for the CDI unit. It was awkward to fit things in and keep wires clear of the rotor arm. The end cap is held on by the Allen head caps screws, one of which can be seen at the top right of your photograph.
If you are going in there I suggest you go very carefully.
thanks Ed careful it is, but I think it needs to be done as its spent most of its life on a racer with long periods of just sitting there
 
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