F4 Magneto

Impulse trips too soon. Any adjustment? Does the small spring at the top behind the cam control the trip?

What do you mean by trips too soon? Does it make a good spark? If it trips before TDC you have to change the little bolts to a different position in the coupler.

The impulse trips before the spring on the coupling is wound tight, resulting in not enough momentun to create a strong spark when it trips.

The trip is done by a cam action that lifts the latch, so it is pretty hard to have it go wrong. It the latch damaged? Is the little spring still connected?

Copy and paste this link to the IH Blue Ribbon Mag Manual into your browser.

(This site won't allow a direct clickable link to post.)

http://www.cleancomputes.com/Cub/Blue%20Ribbon%20Service%20Manuals/GSS-5035%20Service%20Manual%20Magnetos/index.html

The cam appears to not be damaged. The little spring is intact. I can hold the cam down until the impulse is wound tight then let go and get a good spark. Is the little spring supposed to hold the cam down instead of me using my finger to hold the cam down until the impulse is wound tight?
Thanks to everyone. Bob

Kinda hard to describe this without a picture, and pictures here are a miserable thing, so...

The impulse rotor is a split piece, having a front half and a rear half. Above the rear part is a locking pawl that falls down and stops it. The front part continues to turn, and has a ramp on it that comes around and lifts the pawl and releases the rear part, letting it snap forward. Very simple so far.

The pawl also has a little latch that holds it up when running. It's that weird looking little piece that the little spring in the back attaches to. A pair of flyweights behind the impulse keep the latch in place when at speed, disengaging the impulse.

If the pawl or rotor edges are rounded off, the pawl won't hold without some additional down pressure. On a good mag the engagement edges actually go beyond vertical, guaranteeing a positive lock.

If the pawl hinge is dirty it can't fall easily/completely and it may not be completely engage.

The latch may be sticking a bit. It kinda helps push down on the pawl a small amount.

The flyweights may be stuck, causing the latch to not release, but that would cause the pawl to not engage at all.

If the edges are NOT rounded off, it just needs a cleaning and lube.

My two bits.

you may also want to check to see that the rotor gear and the magneto shaft are timed correctly. the gear on the mag shaft has 2 teeth with a small bevel ground into the front face of the teeth. the rotor gear has 1 tooth with a dot on it. when timed properly, the dot should engage between the 2 bevelled teeth.

Thanks for the info. What I called a cam because of it's shape is better described as a pawl because of it's function. I have cleaned and lubed, but it still does not hold. A work in progress.