8hp starts but runs only at high rpms

[Sea Rider]

An old motor should not overheat whatsoever if the impeller, thermostat are doing their homework right and all the water passages are immaculate clean, but nobody cleans them thinking erroneously that flushing the salt with fresh water will take well care of that situation which it's a fallacy. A severe overheat will positively warp the cylinder head, been there twice due to kelp water intake's blockage at full hammer down while the motor was smoking worse than a gang of poker players smoking in a close room...

Happy Boating​

 

[Plandeck]

An old motor should not overheat whatsoever if the impeller, thermostat are doing their homework right and all the water passages are immaculate clean, but nobody cleans them thinking erroneously that flushing the salt with fresh water will take well care of that situation which it's a fallacy. A severe overheat will positively warp the cylinder head, been there twice due to kelp water intake's blockage at full hammer down while the motor was smoking worse than a gang of poker players smoking in a close room...

Happy Boating​

Its a fair point about the over heating. The tell tale was always less than impressive and after the overhaul is now much stronger. I noticed corrosion around the thermostat and now regret that i didn't change it.

 

[km1125]

Well, I guess I'll be the one to call BS on this adventure. Low compression would not cause an engine to run OK at 4000, but not at 3000 or 2000. I could understand if the problems were only at VERY low RPMs, such as the 2-stoke idle problems noted by one poster, but that's just not the case here. Either shaving the head fixed THE problem and now the compression is OK, or shaving the head did NOTHING and the low compression readings were because the OP never bothered to actually check or disable the 'compression-release' mechanism and the low readings he is getting are actually spec (factory manual 'spec', not SELOC manual 'spec'!!). As noted earlier in this thread, the decompression mechanism can allow 'in-spec' compression measurements as low as 42 PSI on similar motors.

The only reason I'm posting this is so that future readers don't go off into some 'wild goose chase' trying to fix something that's not really a problem and hopefully will do more thorough troubleshooting to fix their issue.

 

[Sea Rider]

Its a fair point about the over heating. The tell tale was always less than impressive and after the overhaul is now much stronger. I noticed corrosion around the thermostat and now regret that i didn't change it.

If all the water passages were manually cleaned will surely see a peeing improvement throught the peeing port. If it's still possible to install a new thermostat go for it, motor will cool much better...

Happy Boating​

 

[pvanv]

Well, I guess I'll be the one to call BS on this adventure. Low compression would not cause an engine to run OK at 4000, but not at 3000 or 2000. I could understand if the problems were only at VERY low RPMs, such as the 2-stoke idle problems noted by one poster, but that's just not the case here. Either shaving the head fixed THE problem and now the compression is OK, or shaving the head did NOTHING and the low compression readings were because the OP never bothered to actually check or disable the 'compression-release' mechanism and the low readings he is getting are actually spec (factory manual 'spec', not SELOC manual 'spec'!!). As noted earlier in this thread, the decompression mechanism can allow 'in-spec' compression measurements as low as 42 PSI on similar motors.

The only reason I'm posting this is so that future readers don't go off into some 'wild goose chase' trying to fix something that's not really a problem and hopefully will do more thorough troubleshooting to fix their issue.

That model does not have decompression.