Re: 1975 100 evinrude model100193
The intakes are on the lower unit, grooves on each side. You should see some water coming out of the exhaust ports on the exhaust housing. If you are running on a hose you wil only get water out around the prop. In the water you should get misting out of the exhaust ports.
Your engine does not have a tell-tale, water indicator, but you can install one. Just run a seach, it has been discussed in several posts.