How to compression check Honda BF40?

[T.R. Bauer]

What I said was oversimplified, but basically accurate. I built my share of fast engines....lol....I think it's fun. I'd love to build a 557 Ford, but it's hard for me to pull a perfectly good engine to put another perfectly good engine in...just kills me! And so would the 7 mpg

There just so many variable with compression. One thing I have found is that carbon build up can cause low compression too, when you think the opposite should happen. It's because the carbon is keeping the rings from sealing or the valves from closing. No way you have that with all six slugs. If you've been running them hard, have good power, and are not blowing clouds of blue smoke out the back of your boat at full throttle, things are likely just fine in that area. It does sound like your carbs are dirty though from your description. Taking them apart and cleaning them up is not too terrible and there are good videos on youtube that show it. Also, adjusting your valve clearances can help with compression too, but only if the clearance is too tight. I wouldn't not touch it if you have good strong power - things are likely fine. Honda 40s and 50s are one of the best outboards made in my opinion.

[Barry Rietz]

Any time you are evaluating the condition of a high hour four stroke engine, doing a cylinder leakage test (warm) will provide a better overall assessment of the combustion chambers condition.