Tohatsu MFS3.5 stopped then started up fine

[Mark SF]

Tohatsu MFS3.5 4 stroke, 1 year old.

I was cruising along on a lake this weekend, at full throttle. The lake is at 7000ft and I've noticed before that it doesn't run as well at altitude as at sea level.

Anyway, the revs just began to drop and drop, until the engine had stopped. It started up again right away, and ran fine for the rest of the trip, another 30 mins.

Any idea what the issue might be?

 

[Sea Rider]

Re: Tohatsu MFS3.5 stopped then started up fine

Engines works perfectly well at altitudes of up to 800 Mt, looses about 15% each one thousand meters high, if tank vent was properly opened, probably a acclimatizing air/gas issue Use low octane fuel while at high altitudes and play with prop pitch to better engine lost speed and performance.

Happy Boating

 

[pvanv]

Re: Tohatsu MFS3.5 stopped then started up fine

What Luis said, plus... there is a high altitude jet kit available if you will be running up high for a while. If you will be changing altitudes a lot, you may want to get another carb, and have one jetted for altitude... the other jetted for sea level. Also, since this is a gravity-feed fuel system, be sure that the transom tilt doesn't cause fuel starvation when the tank gets low.

 

[TOHATSU GURU]

Re: Tohatsu MFS3.5 stopped then started up fine

That engine is drowning in fuel at that elevation. A high altitude jet kit is mandatory.

 

[Sea Rider]

Re: Tohatsu MFS3.5 stopped then started up fine

Asked high altitude issues to Tohatsu Japan sometime ago, seems have very little experince with engines working at high altitudes, recommended me to check with 3.5 Mercury/Mariner brands as they are more experienced on this subjetc. I know there are kits available to match different altitudes, can pick best in terms of a given number/code (part number changes every one thousand meters high)

If using engine that often in coast and lakes what recommends Pvany is the way to go, if impossible to find those kits, low octane gasoline and prop pitch change is a must to peform better, not optimum, at least much better than rowing

Happy Boating

 

[TOHATSU GURU]

Re: Tohatsu MFS3.5 stopped then started up fine

http://internetoutboards.com/partdetail.asp?id=1039

 

[Mark SF]

Re: Tohatsu MFS3.5 stopped then started up fine

Thank you for the info. I think what I would like to do is keep it optimised for sea level, where sometimes my life depends on it, but have it work a bit better than it does right now at altitude.

If I can do that by switching to lower octane fuel and swapping the prop to a lower pitched one, I would be happy. I will try 87 gas and the next lower pitch prop next time I go to the lake. It actually has enough power for me at altitude, it's just a little temperamental in terms of stalling etc.

Should I be using 87 all the time anyway? It's on 91 right now.

Asked high altitude issues to Tohatsu Japan sometime ago, seems have very little experince with engines working at high altitudes, recommended me to check with 3.5 Mercury/Mariner brands as they are more experienced on this subjetc. I know there are kits available to match different altitudes, can pick best in terms of a given number/code (part number changes every one thousand meters high)

If using engine that often in coast and lakes what recommends Pvany is the way to go, if impossible to find those kits, low octane gasoline and prop pitch change is a must to peform better, not optimum, at least much better than rowing

Happy Boating

 

[Sea Rider]

Re: Tohatsu MFS3.5 stopped then started up fine

Pvany and TG has given wise clues to go for, but as you state just looking for bettering the engine performance without swapping carb parts, don't have information on 3.5 4T engines, only work with 2 strokes same engines 2T has 6 & 7 pitch props, plastic and alum ones, probably same for 4T engines Go for the one that gives best push rather than speed as you already loosing a lot rpm's at high altitude.

About gasoline octanes, being a low compression engine lowest one asume will work perfect for both applications, would be an issue to have 91 for coast and change leftovers for 87 for lake use. If you haven't tried 87 at sea level before, experiment and test for yourself if you lost some performance. If not, use 87 octane and swap props for both applications accordingly.

Happy Boating