Misc: Ignition Optimum Kickstart Ignition Advance

Oldhaven

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I'd like to get some opinions about the optimum kick starting ignition advance number for a normal road going twin or Comet. (close to factory size carbs, 7or 8 to 1 compression, 140 to 190 pound 65 to 75 year old kick starter pusher, magneto replaced by a coil system). I know the factory provided the ATD and Lucas distributor which were theoretically set to 4* BTDC static timing, and I have heard this figure repeated many times on this forum and elsewhere.

I am asking since the programmable ignition I am using has this curve as its default setup:

vincent 1.0 first.jpg


It is a multi spark system with three sparks. As you can see, at kick start speeds the first programmed spark occurs at 12 BTDC, the second at 5, and the third at 0. I don't have too much trouble kick starting my Rapide, generally 2 or 3 kicks from cold and first kick when warmed up. I very occasionally get a pop through the carb when cold starting. I can easily change this and I may reprogram to a lower first spark when I get up north to the summer place where the bike is hibernating for the winter, but I hope I can get some opinions about whether it makes any difference that the starting advance at very low engine RPM's is 8* higher than the factory recommendation. I can change that and not affect the rest of the advance curve.

As a related question, what is the average kickstart RPM, given a good stroke with follow through?

We have 3 twins running on this system now.

Ron
 
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vibrac

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12 BTDC did I read that right?
Is that an invitation to kick back, what do others think?
 

Oldhaven

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I think I need to clarify what I wrote above a bit. I can see that it can be confusing. The way this ignition works is that during installation it is timed to TDC with an LED and degree wheel in the normal manner (or at least normal for an electronic ignition). After that when the engine has been put into what you want for a starting position you turn on the ignition and and kick . It will fire at 0*/TDC when it sees it for the first time. After that it goes to its programmed settings as shown in the chart above. I think 12* would be a bit too advanced for that first firing, but it should not kick back at 0*. The ignition will reset to the initial resting state if it sees no motion of the encoder, (if it does not start) and the starting sequence firing at 0* TDC will be re-enabled. I do notice that Pazon and some other starting curves are lower than 12 (about 5*) at starting and low idle and flat up to about 500RPM, so I was curious what your experiences have been.
 
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Vincent Brake

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I use on all bikes a pazon for the last 5 years. The high end one (well..)
And do very rare have a slight kickback, and a bit more a smoke cough from the carbs.
I run with mikunies 28. Bit on the rich side.
And a 1:8 or 8,7 comp.
When cold or damp from overnight i need 2-3 hard kicks. With releasing the valve lifter at the end to start it.
 

greg brillus

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Kicking speed at the engine is around 250 to 300 rpm, the Vincent engine likes around 4 to 5 degrees initial advance. If you run close to or around TDC the engine will be hard to start and the exhaust pipes will get very hot at low engine speed, anymore than about 8 degrees can start to kick back if you are a bit " Limp wrist ed" with your kicking effort. Full advance using modern fuels and normal compression's between 7 and 8 to one ratio I use 34 to 35 degree max, some get away with more, but this could well depend on the fuel used and your local climate. The old school Hemi combustion chambers of all old bikes and modern fuels do not go so well together.
 

Oldhaven

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Thanks Greg, just what I was looking for. I hope to get some dyno time this year to test out a few new ideas. The advance of technology and the availability of programmable ignitions may require some rethinking of old dogma since we have so many options available. I will at least drop the first spark after 0 to 10 BTDC. I wish I could reprogram my personal ignition this easily.
 

vibrac

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I don't think you will get a better summary than Greg's ,every engine is a little different the Dyno or a rolling road is the only way to get it spot on.
Do put an m8 boss on the back side of the exhaust pipes about 10 inches from the ports for a lambs sensor for the testing, stuffing a probe up a dirty silencer is a poor substitute.
 

Oldhaven

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A friend of mine sent me this picture of a temporary adapter he made for a lambda sensor that does not require welding on the exhaust pipes. While not in the ideal location and a bit farther from the port it could even be used on the road.

DSCN3043.JPG


(Later edit---I had a picture of an M8 rivet nut here as an option, but the sensor is M18, so no good for that)
 
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greg brillus

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Hi there Ron, why not just go with what is in the picture.......Just make a short adapter that fits between the end of the header pipes and the muffler. Then just make up a temporary bracket to support the muffler off the right side pillion plate. Most all of these old bikes run quite rich..... and lean off quickly as the throttle is opened, my guess is that it takes a tiny amount of time for the fuel to catch up to the increasing airflow as the slide lifts. They need to run rich being air cooled anyway, but changes in carburetion will show up well using the lambda sensors. If you can change the ignition, you may see some gains there as well, but a dyno wont show the effects of an engine pulling hard up a long hill on a hot day, so be careful what you aim for. Cheers............. Greg.
 

bmetcalf

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Is there much left for the 3rd spark to ignite? Can't hurt and the programmability (is that a word?) is good.
 
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