CONTINUOUSWAVE

I may buy a Yamaha 75c. Is this engine good for a 1976 15-footer?

The [peak cylinder pressure reading] on all cylinders is 100-PSI; is that a problem?
Down the road will [these pressure readings be a] problem?

For advice on how to evaluate readings of cylinder pressure see

Assessing Used Outboard Engines
http://continuouswave.com/whaler/refere ... Check.html

I don’t know how to predict future problems that could occur with the engine under discussion based on the information you provided.

Read more about the Yamaha 75c model at

https://global.yamaha-motor.com/busines ... index.html

My biggest concern [in selecting an outboard engine for a 15-foot Boston Whaler] is engine weight. [Some engine only identified as a] current four-stroke-power-cycle engine weighs 353-lbs, which is more weight than I would want on a classic 15-footer.

If worried about the weight, consider the Yamaha F70 which is 253-lbs. An increase of 100-lbs is a lot for only an additional 5-HP.

Caseycjones wrote:I may buy a Yamaha 75c.

Are you trying to refer to a Yamaha F75C?

Or to the classic two-stroke-power-cycle engine the 75c that weighs about 265-lbs?

Unless you clearly identify the engine, readers can only guess which engine you are asking for advice about.