2000 Tohatsu M40C compression test

[elong0916]

I have a 2000 Tohatsu M40C that still runs good but does not seem to have the same get up and go it used to. Lol

I would like to check the compression on it before I get to in depth, I know the basics;
Warm engine
WOT position
All plugs out
4-5 revolutions

But I'm not sure the correct psi for this engine, if anybody has a manual handy or knows off top of head I would appreciate it.

 

[Sea Rider]

Re: 2000 Tohatsu M40C compression test

Welcome to Iboats,

Being a 13 year oldie, make a spun hub test before making compression test, that way will know current prop is in opt state. How do you know it doesn't have the punch it used to have, did you recorded previous GPS speed and max rpm achieved at wot ? Probably it's just a feeling rather than a mechanical issue. Cylinder compression is 107 PSI. Was that engine heavily used ?

Happy Boating

 

[deejaycee_2000]

Re: 2000 Tohatsu M40C compression test

Engine doesn't need to be warm, it's more about the consistency of the readings than the actual compression .... WOT position will not make a difference ... killswitch must be off and one plug out at a time only and the swing it 4 times ...

 

[elong0916]

Re: 2000 Tohatsu M40C compression test

I did not think about the hub slipping-- will check, thanks.

You are right, maybe it is just a feeling, just seems like it takes longer to get out of water on plane that it used to, maybe I need to start eating less But I am going to replace plugs on it as it has been a while, so checking compression is an easy check.

 

[Sea Rider]

Re: 2000 Tohatsu M40C compression test

Start with prop check, if ok, go to compression check, change plugs, try higher fuel octane, eat less. Warmed engine and throttle to wot is what's stated on the Tohatsu service maual, if helps or not, it's other story. Due to environmental air conditions specially during winter and summer, engine can run with slightly +,- performance variations, but that's normal.

Happy Boating