1940 B Wilco C 477B

I inherited my brother?s 1940 ?B? and it wasn?t running to good. The head was rebuilt and the carburetor was rebuilt/restored. It still didn?t run very well. Hard to start and a lot of back fire. Searching this web forum I learned a lot about the WILCO ?C? 477B magneto. Investigating I found the impulse ?snap? was 180 degree out but the spark wires were previously switch in the cap, so I think this would still permit the ?B? to run. Then I found that the LH IMPULSE occurred about 12 fly wheel teeth AFTER TDC. Searching I found a wealth of information about magnetos and successfully got the timing correct and the 180 degree corrected. Now the ?B? starts easier and actually runs pretty good. I did notice on the rear of the magneto, 11 index marks stamped into the housing. I mentally number these 1-11 with #1 being the far left and #11 being the far right with #6 in the center. I also notice a single index mark on the center core which is held stationary by 4 screws. Releasing these 4 screws, the core will move across the 11 stationary index marks.

What are these index marks?

At this time the single index mark on the center core is position to the left of #1, fully to the left (CCW).

Is this good or bad?

Thank you in advance for you insight and guidance.

When you loosen those 4 screws and rotate the plate, you are adjusting the LAG ANGLE which represents how many degrees START IMPULSE timing LAGS the run time advance timing. Its supposed to be set TO MATCH WHICHEVER DRIVE CUP YOU ARE USING. If you use a 35 degree advance drive cup, you adjust the lag angle to 35 and start her at TDC then at 250 RPM when the impulse stops functioning, your run time advance is 35 BTDC.........If you use a 25 degree advance cup, then you adjust the lag angle to 25. If all was well and new and timed right and no slop or wear if shes start timed right at TDC and if the lag angle is correct at 250 RPM when the impulse stops winding and tripping she will fire at 25 BTDC and the mag will be pretty much straight up n down in the center of its adjustment window.

The top center hash mark represents 12 1/2 degrees of lag for a 35 degree cup or a non 6274 25 degree cup and each mark = 5 degrees. Therefore if you have a 35 cup you loosen the screws and rotate the mark 4 1/2 marks to the left. 12 1/2 + 5 + 5 +5 + + 2 1/2 degress = 35 degress of lag.......If you have a non 6274 25 degree drive cup, you set the lag angle to 25 which is 2 1/2 marks to the left, since 12 1/2 + 5 + 5 + 2 1/2 = 25 degress of lag. HOWEVER if you have a 6274 drive cup its a 25 degree cup BUT when using that cup the top center has mark represents 2 1/2 NOT 12 1/2. It would set 4 1/2 marks to left since 2 1/2 + 5 + 5 + 5 + 5 + 2 1/2 = 25 degrees of lag.

They can still start and run if the lag angle is off but this is how it was from the factory and if all is well.

NOTE Yearsssssssssssss ago I gave Wico Mag Seminar Workshops at Gathering of the Green and Two Cylinder Expos but I may have forgot some of it and I did NOT look at my notes, I just winged this from memory and it may be wrong as rain so dont anyone have a calf or bet the farm on this NO FREAKING WARRANTY

John T

How do I determine what cup I have?
I assume the "cup" is the device on the rear with the two dog ears that match to the govenor drive. I did not see any markings or numbers on this.

Usually right on the back of the coupling by the ears it says 25 or 35 stamped in it ??? Now I'm betting yours is the long lug one. That might not be marked ? I think they were all only one type but I forget which one. I worked on way more with the short lugs.

And John that is how I remember them being. Roughly 3 and 1/2 marks from center for a 35* and 2 and 1/2 marks from center for the 25*

Its 4&1/2 marks for the 35%