D2 magneto popping while running

I installed a "new to me" magneto in my D2 pony motor recently. I had done this before on my D69U, so the job was pretty straigtforward.
One problem. The pony starts but it "pops" when it runs. I have to keep the choke nearly open for it to run, I might add. On a cold morning like we've been having lately, it's not unusual to have to keep playing with the choke adjustment for up to 20 minutes before it is running with adequate rpm's.

Once the diesel starts, the pony runs like a dream! Go figure. Prior to that, the pony runs in fits and jerks and drives me up a wall. I get the feeling one cylinder is not kicking in early on in the starting process. Might be wrong on this, sure sounds that way.

I have new plugs and wires, but she sounds like one side is half in and half out. It pops off right away when pressing the starter button, but runs jerky and "pops".

I think points are adjusted OK.

What is the general consensus on this problem?

thanks..

Did you check the small filter on rear flywell if he is plugg your missing air

Hi Gil,
could be the inside of the magneto cap has a carbon track burned across from one terminal to another or simply has carbon dust on its surface which can start the carbon track burning process.

When this occurs the extra load of running cold with a poor mixture puts extra load on the spark system and the spark tracks across the cap to the plug of least resistance.

Newer style Resistance plugs must not be used on magneto ignitions as they overload the coil windings and other components. Some plugs now seem to still have their old Numbers but have been upgraded by their makers to be Resistance plugs--thanks a lot.

I found the link below which shows how to modify a Resistor plug back to Non-resistor. It is a bit slow but gets you there.

https://www.youtube.com/watch?v=5FOtJUbjpoo

If you find a carbon track burn mark on your cap it can be carefully scoured out to remove the carbonised cap material and sealed with Electric Insulating Spray--CRC make one we used at The Dealer. Some people like to fill the groove, after scouring, with two part epoxy--JB Weld-- and then spray seal.

Also check the gap between the end of the rotor button and the cap terminals as the end of the rotor button gets eroded away by the spark jumping across. In the past when the gap is deemed too wide I have soldered a suitable piece of brass on to the top of the brass strip of the rotor button--I think I went for around 0.020" gap from memory.

I also run my plugs at around 0.018-0.020" to help preserve the magneto coil windings.
On some really weak magneto's on my old farm engines I have been known to successfully run plug gaps down to around 0.010-0.012" without fouling etc.

Hope this helps,
Cheers,
Eddie B.

I will beat my favorite dead horse once again.......my somewhat limited experience with ponies that require the choke to be on to run with any power are either
1...experiencing fuel starvation because it isn't getting into the bowl (tank full of ???, valve clogged, line clogged, Float needle problem etc) and choking it really doesn't help much but you choke it and it recovers some after starving out.

2....have a clogged fuel passage or other problem in the carb itself. The first one that must work in the TU4C Zenith carbs used on the horizontal ponies (D2, D4, D6) is a passage drilled across the bottom of the fuel bowl connecting the main jet (the high speed mixture screw sits in it) and the high speed metering well (a passage in the bowl that is plugged with a hex head threaded plug and angles up from the corner of the bowl toward the "bulls eye" gasket where the bowl seals against the cast iron carb body). The hex plug screws out and a brass orifice tube comes out of the vertical/diagonal passage. The horizontal passage across the bottom of the bowl tends to collect debris since the inlet from the high speed jet is DOWN into it and the outlet is UP through the high speed metering well. Drilling one soft plug will allow you to run a drill bit through the passage by hand and clean it out completely. I had sprayed various cleaners through mine and blown through with compressed air, but until I drilled the plug and reamed it out clean, my pony was a weak, temperamental little b******.

Other ponies won't idle which usually requires cleaning the inlet jet in the venturi as described by Eddie B several times on this forum. Mine would idle OK, it just wouldn't pull the diesel without a lot of choke and was temperamental to say the least. I had previously cleaned and relined the tank and installed an inline filter to stop the rust problem, but I had reluctantly come to the conclusion that my pony was worn out(IT IS! it has little compression on one cylinder and rust pitting in that bore) and I was going to have to overhaul it to get it to perform. Cleaned the one passage as described and it does very well now!

I replaced the soft plug with a blob melted off a piece of electrical type rosin core wire solder. Just tamped it into the hole with a small punch and it has stayed put just fine. Others have used lead shot, steel B's coated with shellac type sealer or even tapped the holes
for short machine screws. However you do it, I think it is a good idea to clean the carb passages before you go down too many other trails if you have one that you have to run with the choke on all the time.