#13 - Carburetor and Manifold Power
We know that IH put their small carburetor on the 154, and, upgraded to the larger, more powerful Zenith carburetor for the 185 and 184. This larger Zenith carburetor picked up about 2HP over the IH carburetor. While 2HP may not seem like a lot, an increase in power from 12HP to 14HP is quite noticeable.
It is interesting that the IH and Zenith carburetors will use the same manifold, so they can be easily swapped out. I have always wondered why IH made a slightly different manifold for the Zenith carburetor. This "different" manifold had a slightly larger flange, but, the exact same bolt pattern and inflow port size. So, the 2 manifolds function identically to each other, even though one looks slightly different due to the flange size.
I once had a customer tell me that he used a 1" bore bit to enlarge the port hole from 7/8", and noticed even slightly greater power pickup