Re: Replace your points w/electronic

Paul D /
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I don't have a schematic of what is inside the ignition kit, so I have to make some assumptions.

The ignition kit is made for lawn mower and weedwacker-type type engines which use a different type of magneto and coil . Most of those engines (both 2 and 4 stroke) use an external armature-coil that serves as a primary magneto drive coil as well as the ignition coil primary and secondary (see pic).

http://home.flash.net/~lauras34/moped/spec/armtwor.jpg

The flywheel of a lawn mower engine has a single magnet embedded in the flywheel. The ignition timing on many small lawn mower engines is fixed.

The ignition kit is placed in series with the primary coil of the armature (one wire to ground and apparently the other wire to the armature wire that would have went to the mechanical points). The kit probably senses current in the primary of the armature-coil and opens the primary to fire the plug when the primary current is at a maximum. This occurs as the magnet in the flywheel is passing by the armature-coil.

The next pic shows a typical Bosch ignition from a Batavus moped.

http://home.flash.net/~lauras34/moped/spec/batmagr.jpg

In a moped magneto there are three coils for the ignition: the ignition drive coil, the ignition coil primary, and the ignition coil secondary. One wire of the ignition kit would need to be connected to the ignition drive coil and the other wire to ground (the two wires would be connected to where the points are connected but with the points disconnected). The kit would then sense current in the ignition drive coil and fire when the current is at a maximum.

A potential problem with trying to use the kit on a moped is that a moped magneto has multiple magnets in the flywheel for the purpose of generating enough power in the lighting coils. Assume that the ignition kit senses current generated by each magnet during a cycle. If there are four magnets in the flywheel, the ignition kit would fire four times during a revolution: at TDC, BDC, and when the piston is halfway up and halfway down the cylinder. Firing the plug when the piston is halfway up the cylinder could damage the engine. This would be equivalent to setting the ignition timing extremely advanced. Firing at BDC would ignite the fresh fuel-air that just entered the cylinder.

Some four-stroke lawnmower engines fire at TDC twice during a crankshaft revolution since the flywheel does two revs per complete cycle. This is not a problem on a 4-stroke since the 2nd TDC firing occurs when only exhaust gases are in the cylinder.

The ability to easily set the ignition timing mechanically would also be lost since it is no longer determined by mechanical points. Timing would have to be done with a timing light. The timing could still be altered by rotating the stator plate. This would change the position of the ignition drive coil relative to the magnets in the flywheel and change the ignition timing, similar to how a CDI ignition works.

I may be wrong, but the possibility of multiple magnets in the moped magneto firing the plug multiple times during a revolution is what concerns me the most. I would try it first on a moped engine that I don't care about. It should work well with lawn mower engines, though.

Paul

This single post is part of a larger thread. Start from the top or view this post in context.
Subject Written By Posted
  Replace your points w/electronicTopic by: Brian Brian 11/11/01 12:15PM
  Re: Replace your points w/electronicRe: Mike (MA) Mike (MA) 11/11/01 08:20PM
  Re: Replace your points w/electronicRe: don-ohio don-ohio 11/12/01 05:19AM
  Re: Replace your points w/electronicRe: don-ohio don-ohio 11/12/01 06:13AM
  Re: Replace your points w/electronicRe: Roberto Roberto 11/12/01 11:22AM
  Re: Replace your points w/electronicRe: SteelToad SteelToad 11/12/01 02:06PM
  Re: Replace your points w/electronicRe: ken ken 11/12/01 06:45PM
  Re: Replace your points w/electronicRe: don-ohio don-ohio 11/16/01 03:46PM
  Re: Replace your points w/electronicRe: mopedmonster mopedmonster 12/05/01 12:00AM
  Re: Replace your points w/electronicRe: Tab Patterson Tab Patterson 11/06/02 09:10PM
  Re: Replace your points w/electronicRe: Shane Wolfe Shane Wolfe 11/06/02 09:27PM
  Re: Replace your points w/electronicRe: Casey B Casey B 11/06/02 10:59PM
  Re: Replace your points w/electronicRe: Ike Fist Ike Fist 11/08/02 11:37AM
  Re: Replace your points w/electronicRe: Shane Wolfe Shane Wolfe 11/08/02 09:00PM
  Re: Ike, You replace your points w/electronicRe: Michael Reed Michael Reed 11/19/02 07:13PM
  Re: Ike, You replace your points w/electronicRe: Tab Patterson Tab Patterson 11/19/02 11:22PM
  Here is the Link for the CDIRe: Bill W Bill W 11/08/02 10:48PM
  Re: Ike, You replace your points w/electronicRe: Freeman Montgomery Freeman Montgomery 11/19/02 07:28PM
  Re: Replace your points w/electronicRe: Paul D Paul D 11/20/02 06:19PM
  Re: Replace your points w/electronicRe: Michael Reed Michael Reed 11/20/02 11:55PM
  Re: Replace your points w/electronicRe: Ike Fist Ike Fist 11/21/02 04:24AM
  Re: Replace your points w/electronicRe: Paul D Paul D 11/21/02 09:08AM
  Re: Replace your points w/electronicRe: Michael Reed Michael Reed 11/21/02 10:24AM
  Re: Replace your points w/electronicRe: Tab Patterson Tab Patterson 11/23/02 10:09PM
  Re: Replace your points w/electronicRe: Michael Reed Michael Reed 11/24/02 12:04AM
  Re: Replace your points w/electronicRe: Paul D Paul D 11/24/02 01:48PM
  Re: Replace your points w/electronicRe: Matt Wilson Matt Wilson 11/24/02 10:58AM
  Re: Replace your points w/electronicRe: Michael Reed Michael Reed 11/24/02 12:54PM
  Re: Replace your points w/electronicRe: Paul D Paul D 11/24/02 01:43PM
  Re: Replace your points w/electronicRe: Michael Reed Michael Reed 11/24/02 02:09PM

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