Adjustable ignition timing

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2door

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Cannonball hit it on the head with > (The trick is determining where exactly the rotor triggers the ignition.)

When you say the ignition is advanced or retarded I'm curious as to what you are referring to. Piston position? Crank position? Due to the fact that the magnet's effect on the coil is what determines when the CDI fires, knowing the triggering point is what you'll need to know to use any information you might get with a timing light, a degree wheel or a dial indicator.
When I did my experimentation I had no idea where the CDI fired in relation to the magnet's position in the coil. A timing light might help if the magnet is marked and the engine would need to be running, not just being cranked over. I had a good timing light but a friend dropped it and instead of replacing it, he paid me in cash.(Warning: never loan tools) I haven't replaced it yet. I just winged it and used comparisons taken from four engines that all were different in regards to exactly where the key way in the shaft was at TDC. I then 'advanced' the magnet's position on the worst running engine, the one which incidently, measured 3 degrees less than the best running engine. I cut a new keyway in the magnet and the results were dramatic. The worst running engine now ran as well, maybe a little better than my best one. This being the case I have to disagree with Jim's advice that the engine will need bolt on performance parts and modifications to get the benefit from advancing the ignition. Certainly if you're looking for the absolute maximum performance increase then mods and parts will help but they aren't necessary to see a marked improvement in engine performance/output.

I had machined a neat little adapter to fit my crankshafts and hold a cam degree wheel, but...I've misplaced it. I've looked for the darn thing several times and can't find it and since I retired I don't have access to a machine shop anymore to make another one. I'd like to play with this concept a little more and learn a bit of trickery that might be of use.
Keep us posted, Jim.
I'm also intrigued with the R/C plane ignition idea. Has anyone played with this?
Tom
 
cannonball2

cannonball2

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Here is a pic of the typical R/C system. They are designed to run on 4-6v for the most part, however some have a larger range from 3-18v. It might be possible to run off the lighting coil if it produces enough voltage at starting speed. These are pretty much plug n play wiring wise. The plug lead is also shielded so the wireless tachs would benefit there. Cost on this system is around $35. For what ever reason the magnets are not included, but sell in the $1 range.
 

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cannonball2

cannonball2

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No thats the sensor for the magnet. The magnet is normally in the prop hub. The unit fires every time the magnet passes the sensor. Can theroticaly be mounted to anything turning at crank speed.
 
corgi1

corgi1

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That makes sense ,one of the reed switches,,,that may be easy on the small gear side then ,at the front of the motor,on the clutch cover side....they already have/build centrivical clutch covers ,for that side w/the bulge space in that location,thats lots of room for that small switch,.
 
corgi1

corgi1

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I thought I read earlier that the HT was recomended to stay at the lower compression area (6/1?)to avoid doing in the rod and wristpin bearings
 
Russell

Russell

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Jim,
Wouldn't it be easy to broch a new keyway @ 185 deg. and use that. Along with using the new keyway would I also have to flip the armature over to keep the proper magnetic polarity.
Of course I realize that this would only work on some motors and that a completely variable setup as you described is the way to go.
 
corgi1

corgi1

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wonder at what point of the delicate manufacturing the crank parts they cut the key-way,before they press it togeather or after(see the guy eye-balling it ,then wack wack wack with a 3 pounder ,ah so,that looky good)
 
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corgi1

corgi1

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Or you might get a school protractor and carve a half circle hole to fit the shaft at the flat plastic center point
 
Venice Motor Bikes

Venice Motor Bikes

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Mar 20, 2008
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jaguar said:
My idea of crank rotation was opposite of what I'm used to with motorcycles so the gain I got was actually from retarding the ignition, not advancing it. Testing it advanced today gave poor results but the carb needed to be made leaner on the main. Doing that may give the best results yet.
Click to expand...
I tried your idea of just removing the key to advance the timing, & it seemed to run a little better but it was 4-stroking bad at full speed... (So it's hard to tell if it really was any better??) :rolleyes:
I will test more tomorrow & post! ;)
 
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Goat Herder

Goat Herder

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Apr 28, 2008
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AFFECTS OF THE IGNITION TIMING

Here is how changes in the static ignition timing affects the power band of a Japanese dirt bike. Advancing the timing will make the power band hit harder in the mid range but fall flat on top end. Advancing the timing gives the flame front in the combustion chamber, adequate time to travel across the chamber to form a great pressure rise. The rapid pressure rise contributes to a power band's "Hit". In some cases the pressure rise can be so great that it causes an audible pinging noise from the engine. As the engine rpm increases, the pressure in the cylinder becomes so great that pumping losses occur to the piston. That is why engines with too much spark advance or too high of a compression ratio, run flat at high rpm.

Retarding the timing will make the power band smoother in the mid-range and give more top end over rev. When the spark fires closer to TDC, the pressure rise in the cylinder isn't as great. The emphasis is on gaining more degrees of retard at high rpm. This causes a shift of the heat from the cylinder to the pipe. This can prevent the piston from melting at high rpm, but the biggest benefit is how the heat affects the tuning in the pipe. When the temperature rises, the velocity of the waves in the pipe increases. At high rpm this can cause a closer synchronization between the returning compression wave and the piston speed. This effectively extends the rpm peak of the pipe.
 
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