Mac motor ID needed

[Jeffrey Sligh]

Trying to figure out which motor this Mac is, I'm thinking it is a 91, but I'm not 100% sure since I'm not fluent in Mac. Didn't see an engine area on here, so I figured I'd put this here since I know the motor was bought before 1972.

Flywheel side:

  IMG_20200203_162038.jpg (Size: 1 MB / Downloads: 19)

Dual Carbs:

  IMG_20200203_162124.jpg (Size: 1.11 MB / Downloads: 10)

Clutch side (BTW, which clutch is this? Horstman?):

  IMG_20200203_162547.jpg (Size: 1.12 MB / Downloads: 14)

Back of the motor:

  IMG_20200203_162616.jpg (Size: 1.42 MB / Downloads: 11)

[Scott Elkes]

You are in the right area (Mc-91 series). It is definitely is a 100cc McCulloch. I think I see a head gasket, that would rule out the next generation Mc-92 that used an o-ring. I'm not 100% sure, but could rule out Mc-93 due to color. (Horstman spec'd out with McCulloch 93 and 101b engines and was sole US distributor pruchasing the kart engine production run. Believe the Mc-93 was red and white).

Removal of the clutch and exhaust header with a clear picture of that side showing exhaust port and bearing seal will provide significant information for an i.d..
Mc-92 shown...

  IMG_2303.JPG (Size: 1.88 MB / Downloads: 15)

  IMG_2294.JPG (Size: 1.33 MB / Downloads: 9)