4hp outboard runs inconsistantly

Hi all,

I have a 2007 4hp 4-stroke Tohatsu (I think it's a MFS4B) that I use to motor my 25' Coronado sailboat out to the lake that's a mile away.

It starts on the first or second pull when it's cold, every time, and runs great! Then, I motor a mile out to the lake, kill the motor, and sail for a few hours. The outboard sounds great - no issues.

The last two of times I've sailed the boat, I've had problems when I'm motoring back from the lake. The outboard starts after 1 or 2 pulls, but sounds different. Instead of the sharp tatata sound you'd expect from the outboard, it's a duller and quieter-sounding dadada. And when I try to run the outboard at low throttle (as apposed to medium), it dies after a couple of seconds and won't start. I try everything - a combination of high and low throttle, choke in and out - but nothing.

Then, I get a tow back to the marina, and try to start the outboard the next day, and it's back to normal.

I've already cleaned the carburetor with carb cleaner, and the fuel filter looks ok (there is a pretty big air bubble in it, but I read that this is normal). I'm at my wit's end - most problems with motors like this seem like they should be all-or-nothing, not intermittent!

One thing that could be affecting it is that the boat tips when I sail, maybe 30 degrees either direction, which also tips the outboard. Could this be enough of of an angle to mess up the outboard?

I would go through all the basics. Verify the oil is not a drop over full. It must be between the hash marks on the stick. Do you turn off the fuel valve when sailing? You could flood the carb otherwise. When you say that you cleaned the carb, did you do a complete disassembly, including jets and emulsion tube nozzle, and a 4-hour soak of all non-rubber parts, and then a thorough blow-out of all passages?

Hi Paul,

Thanks for the reply. I'm new to outboard motor maintenance (and carburetors!), and I'm realizing that they are a bit more picky than, say, a fuel-injected car engine. A few notes:

- My oil level is indeed a bit too high (I'm used to working on car engines that don't care too much if there's a bit of extra oil).
- I haven't been turning off the fuel valve when sailing. I had thought that the valve just switched between internal and external fuel tanks, but it sounds like I am confused. I took my outboard off of my boat today for 30 minutes, and leaned it at a 30-degree angle (with the carb side facing down) to see if it would cause carb flooding problems, but the outboard started up, first pull, and sounded great! So it seems unlikely that the carb flooding while sailing is the issue. (I'll start turning the fuel knob off while sailing, regardless!)
- I cleaned the carb with carb cleaner recently (doing a complete disassembly, including jets and the emulsion tube nozzle (I think!). I'll do a bit more research about cleaning procedures and go back through and do a more thorough cleaning with a 4-hour soak. (Also, I had similar symptoms before cleaning the carb, so I don't think I messed anything up with the disassembly/reassembly procedures).

I'll have time to do some work on this (carb cleaning and oil draining) on Monday, and I'll report back. Thanks!

The fuel valve allows flow from the integral tank. If it is horizontal (should be if not running for a few days, or the gas will sit and varnish the carb. When dowm, it allows flow from the integral tank. If running from external tank, it should be OFF.