Strange Tohatsu M40D2 problem - WOT shutdown

[Troutboy NZ]

40hp, 2006. Engine well maintained. Just latley after running WOT for 20-30 mins or so the engine will suddenly shudder and die. Starts back up fine, accelerates perfect, no vibration, then will stumble quickly and die again, sometimes after 5 mins, sometimes after 20 minutes....

Now, have check all fuel lines for kinks, leaks, replaced the water separating fuel filter, eliminated the engine coupling by plumbing fuel line direct to the carbs bypassing the engine filter (have Racor instead) - problem still persists. Check primer bulb - all ok. Has me stumped.

Tried new plugs, checked for heat damage - no overheating, wires all intacts, coils tight. I'm thinking fuel-stavation related. Have an internal aluminium tank, quite new and it is permanently vented (checked vent - all clear). Fuel is fresh - no water in fuel trap.

Idles and accelerates perfect, carb cleaned within the last 6 months an was operating fine after that. Would a fulty fuel pump diaphram cause this intermitent problem? Was all fine 6 months ago when checked, but the issue comes and goes, ran 30 mins last night and all sweet - then stumble... dies, start up, go again... problem only evident at WOT.

Any suggestions welcome.

 

[pvanv]

Re: Strange Tohatsu M40D2 problem - WOT shutdown

If the motor immediately restarts (without any fuel priming), it may not be starving for fuel. Especially since the plugs did not seem to be running lean. Of course, checking/replacing the fuel pump diaphragm and valves is not expensive or complex. But I would also check to see if there is any ignition wiring with a marginal connection.

The difficulty tracking down an intermittent failure is that you need to actually diagnose while the problem is occurring, which is hard to do since it restarts so easily. Grab your trusty Factory service manual, and go through the fuel and ignition systems with a fine-toothed comb, paying particular attention to resistance readings on the ignition bits. Try to test right after it stumbles. Of course, verify that you don't have an exhaust leak from the base gasket, which might only show up (choking on its own exhaust) at WOT. You can test that by running with the cowl off, though that also makes the CD and stuff cooler, so it affects more than just the airflow. But it's still a good test to make -- just keep in mind that it (slightly) affects multiple things.

 

[deejaycee_2000]

Re: Strange Tohatsu M40D2 problem - WOT shutdown

CHeck those reeds ....

 

[380voltz]

Re: Strange Tohatsu M40D2 problem - WOT shutdown

Hi ... did u ever find the problem? I have an m40d2 2006 and today was the first time something similar happened to me.

cheers