Yamaha 40, 4stoke spark plug fouling?

Neils Fry · 05-25-2009, 03:02 PM

I troll using my 4 stroke Yamaha 40 with an EZ Troller plate down at about 1 to 1.5 mph or just above idle. Engine has less than 50 hours. After 10-20 minutes, engine begins operating roughly. If I don't increase speed/rpm significantly, the engine eventually stalls. Engine runs great the rest of the time. I suspect plug fouling. Anyone experienced similar problem with a 4 stroke outboard? Perhaps go to a hotter plug?

Bloom · 05-25-2009, 06:05 PM

It could be running a tad lean at that rpm. Have you pulled the plugs to see how they read?

smalldog · 05-26-2009, 08:59 PM

You say it only has 50 hours..did you do the 10 hour service and change the plugs at that time?
They put alot of prelube and stuff in new motors.
Trolling with a new motor that hasnt really been broke in may be contibuting as well.

Lead Bouncer · 05-30-2009, 12:20 AM

I thought plug fouling is oil related. If a four stroke runs bad, its either bad gas, too lien or too rich. Check the book and find out if you have the correct plug.

TundraIII · 06-01-2009, 02:42 PM

I have this exact same problem with my 115 hp yammie 4 stroke. At low idle it's really rough and dies constantly...high idle it runs great. Plugs are "dry fouling". So I'm thinking motor isnt getting hot enough or maybe fuel mixture is wrong. I'm already running a hotter plug. Let me know if you figure something out and I will do the same!