Sisson Choke

[Niel Hoback]

Just to clarify, heat does not turn off the power to the coil. Power stops when the starter stops.

[Joe Flanagan]

So I'm going to replace the insulation on my two apparently burned up Sisson chokes and test them in this way. Who knows? Maybe they're still good.

"Prestodigitorium?" How the heck did I make it through nine years of this project without that word?

[woodie49]

I have two that both seem to have their troubles, so I'll try the repair. What I still am confused about is whether it is possible for the sisson to short after you stop cranking. The more I think about it, I have to beleive that it is not. It should simply be connected to a non-charged circuit as the wire to the starter should not be charged because the solenoid is off to that wire. I guess if that were not the case, I would hear the starter trying to engage - a sound we would all recognize immediately.

So, I am back to how can hooking this up cause me to be frying insulation several minutes after starting? I am guessing that once started, even if I grounded the sisson wire, there is no negative charge available for it to short to.

Any input is very much appreciated.

[Joe Flanagan]

Suppose the electromagnet in the Sisson choke shorted out and fused into the closed position? I was thinking that might keep power going to it when it wasn't supposed to, but then once you let go of the key and stop cranking, the power is discontinued, so that would kill that theory.

[Young Ed]

Could it be that the wire just can't take the heat of the engine? Its possible its not an electrical issue and the wire is just melting from engine heat.

[woodie49]

Could it be that the wire just can't take the heat of the engine? Its possible its not an electrical issue and the wire is just melting from engine heat.

Well, I did not pull it off the starter, figuring I would repair the sisson and re-try it (or maybe re-fry it?). But. since it is still connected, I should still smell it melting. The sisson connection does not look like it got at all hot and I am pretty sure I insulated the terminal enough not to short.

I should just re-connect it and see what happens, but I am afraid of shorting the charger or something. And really seeing what happens could be fairly disasterous.

[woodie49]

The solenoid is only about 6 months old, but, would it be possible that the soenoid is allowing just a small amount of voltage to charge the cable to the starter? Not enough to actually engage it, but enough to slowly heat the 12 gauge wire to the sisson?

[Joe Flanagan]

You should be using 16 gauge wire to the Sisson choke. I don't know that a bigger wire would harm anything, but that's what the wiring diagram calls for.

[woodie49]

I took the sisson apart as discussed earlier in this thread. The insulation pretty much just crumbled when I pulled the top off. That leaves a circular part that forms the terminal connection on the outside. My question is that underneath this part there is a small peice of material that seperates this from the coil or other inner workings. On mine, you can see where it is torn or broken. It is a very thin peice of material. Any idea if this is also an insulating peice? I am wondering if, after I put this back together, this mightl still cause a short.

Sorry, the pictures are from my phone and not great quality.

[Joe Flanagan]

In the interest of science and the hobby, I tried the repair described above to one of my non-functioning Sisson chokes. The insulating material was dried up and in pieces as shown below:

I cut a new piece using gasket material of the same thickness, put the choke back together, installed it, and tried it out. Result: Failure. Fried the lead from the starter to the choke instantly. Tom Skinner has posted that he has done this repair successfully, so I know it's possible. When I get time I'm going to take it apart again to see where I might have gone wrong, but I suppose it is possible that they can short out and then be permanently damaged.

[woodie49]

I have one apart that I am going to try to fix as well. But, in the meanwhile, I have a second (bad) one that I simply hooked up and adjusted without wiring it up.

When it is cold, the choke is in the full-closed position, and once the engine heats up, it is full open. It is actually working quite well this way.

The only think I guess I am missing is when it is heated or partially heated, the Sisson would close the choke while cranking, subject to override by the pedal. MAYBE this would help in starting when hot. But for now, it works a lot better than the manual arrangement I was using.

It is actually behaving nicely now.

[Joe Flanagan]

Well, I've got one more that I haven't tried yet and I hope it works. I'm getting tired of trouble with Sisson chokes. It's a nice little job taking one of these things apart, cutting the gasket, and then putting it all back together. To be honest with you, I don't know if I have the patience to try it again. I have no idea why the one I tried to repair shorted out. I paid close attention to the length of the screw at the terminal.

[Jim Yergin]

To be honest with you, I don't know if I have the patience to try it again.

I find that very hard to believe. Joe, if there is one thing you have shown you have in abundance, it is patience.

Jim Yergin