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  1. K

    1981 Mercury 7.5 2 stroke

    Sorry. Yes smaller ports on 7.5 compared to a 9.8. I did some internet searching. I found some posts where folks were claiming 100, another 165. https://forums.iboats.com/threads/compression-for-a-7-5-hp-mercury.236135/...
  2. K

    1981 Mercury 7.5 2 stroke

    My understanding is piston rings wear over time and compression slowly drops. There does not need to be any visual damage to piston or rings for compression to be low. Could just be a tired engine. Maybe 70 or 80 psi is all these 7.5 hp engines ever made. Looking to confirm. The 9.8 and the...
  3. K

    1981 Mercury 7.5 2 stroke

    The Mercury Shop Manual I ordered arrived. It covers the smaller Mercury outboards, including my 7.5 HP. I was hoping to find stock compression numbers. They don’t publish them in the book. Can anyone tell me what the compression should be on my ‘81 7.5 HP engine. I have measured my engine and...
  4. K

    Possible water intrusion or lean sneeze?

    Possibly related: When storing a two stroke; standing upright is ideal. If laying down, spark plugs are to be up. This keeps the cylinders higher than the prop. Residual water in the cooling passages can flow into the cylinders if stored incorrectly. While stored, this water will cause piston...
  5. K

    1981 Mercury 7.5 2 stroke

    Thanks. I will try those web sites. I have already pulled the lower leg measured, the shaft and ordered a water pump. Its on the way. The thermostat was removed. I also ordered one.
  6. K

    1981 Mercury 7.5 2 stroke

    I recently purchased a used 1981 7.5 hp outboard. I plan to use it with a small SIB. I am new to outboards but not new to mechanical repairs. I’ve rebuilt multiple other types of 2 and 4 stroke engines. I tend to source an OEM service manual ASAP. I’ve not found one yet but I will. Is anyone...
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