Question about those devices that eliminate points on older mowers such as "D" series

[Phototone]

Question about those devices that eliminate points on older mowers such as "D" series

Older Lawnboy mowers with "C" and "D" series engines often have points unless very late model D-600 engines. Those engines that have points have a mechanical centrifugal advance that allows easy starting with the timing retarded, then as the engine speeds up advances the timing for efficiency and power. I found an old D-400 series mower I am restoring that has had one of these devices added, and the points and condensor removed from the circuit. It gives a good spark with the original coil, but I wonder if the retard-advance feature on these Lawnboys is not present in the solid-state replacement for the points. Its a very tiny little thing. I am probably going to put it back to points and condensor, as I like things original. Any observations on these devices?

 

[Kerry]

Re: Question about those devices that eliminate points on older mowers such as "D" se

I was hesitant to answer because I have no firsthand knowledge, but I am also a member of the Antique Outboard Motor Club and have read posts from members that have used them. The main two brands are Atom and Nova. These modules basically replace breaker points to eliminate the problems associated with them- kinda like a poor man's CDI. The users report easier starting, improved idling, and smoother trolling. Again, this is secondhand. If you do remove it, keep it just in case. One member uses a Nova module to see if errant running is ignition related.

 

[motoman]

Re: Question about those devices that eliminate points on older mowers such as "D" se

There is a site catering to tractor pull which discusses the "trigger" transistor for 4 strokes , but don't recall discussion on 2 strokes. If most (?all) 4 strokers run at about 3000 rpm doesn't seem they need any advance, but the site mentioned does install auto type advance into the AC engines for more power. As you guys know the little 2 strokers make their power way higher up so I would expect advance, but have not found discussion. We need to mark TDC and provide a little window so we can hook up a lite and watch.

 

[motoman]

Re: Question about those devices that eliminate points on older mowers such as "D" se

photo, I did search this am and found a patent from 1971. Two guys working for motorola developed a system without transistors, but with diodes and capacitors that advance timing based upon rpm. The curve starts at 3 degress BTC and advances to 15 degrees at 2000 rpm, where it flattens out to about 18 degrees at 9000 rpm. It is a magneto system. The key word is "shaped" core pieces which are stationary. As flywheel rpm increases the spark occurs sooner. There are probably aftermarket solid state bolt-ins , but very sensitive to bolt-in position, and so specific to a brand. None of the vendors show how the advance occurs, but do advertise it.

To me , the Briggs magnetron magneto (my 4 stroke intek) simply produces spark at a set (?advance?) point. But the little 2 strokers need an advance curve to produce power which seems to be at around 7000 rpm.

Edit PM: OK so reread patent 3,599,615 several times. An example is given of a coil for a chainsaw. The "shaped core" is a second metal shoe (and coil)kissing the flywheel with a gap that is wider at one end (.153" ) than the other (.010"). This is like the gap on the Briggs set to e.g., business card thickness (.010"). The unequal gap produces the spark advance. I looked at my dead Ryobi 2 stroke trimmer, and it appears to be that module.

If this isn't more than you want to know we can discuss it further.:biggrin:

 

[robinb66]

Re: Question about those devices that eliminate points on older mowers such as "D" se

try this link :thumbsup::thumbsup:https://www.scribd.com/doc/3565537/Make-Your-Own-CDI