Tohatsu 50D - Problem not fixed yet

[hvaldezz]

Gentlemen: Thank you for all the inputs. The Tohatsu mechanic ordered new kits for the carbs. The mechanic who did the initial cleaning did not install kits. Kits are in today, Monday May 12.

Kits are to be put in today and will try again tomorrow afternoon. Tohatsu says the problem is not electrical based on the inputs the mechanic has passed on.

Several of you are pointing at fuel problems (starvation) as the culprit although cracked manifold, bad plug wires, etc. are good inputs.

At this point, the consensus says: Fuel problems and I guess I will have to go along with that. I did kinda' like the start it up at night in the darkest dark to see if any sparking occurs.....but best of all, I liked the 3:02 p.m. suggestion. Am I going batty because of this problem? A resounding yes as I would have thought all the collective minds would have solved this problem a long time ago. This engine problem is cutting into my sailing time, work time, sleep time, and who knows what else.

Will advise on our findings. Don't know what else to do right now, I thought this was going to be easy......

Henry

[pokerrick1]

I did kinda' like the start it up at night in the darkest dark to see if any sparking occurs.....but best of all, I liked the 3:02 p.m. suggestion.
Henry

You're welcome

And you other guys thought I just post friviously (sic?)

Rick

[RickJ]

Hello,
That would be my first thought too but the mechanic said he serviced the carbs. Maybe he put a couple of floats in upside down.

Yes, even experienced mechanics can get it wrong.

My X that I bought last year came with a Suzuki 55 2-stroke 3-cyl that hadn't been run for over a year. I asked the local agent to service it, they stripped and cleaned the carbs and got it running, but very rough. They told me they could spend loads more hours on it, but it might end up costing me more than it was worth, or I could take it home and sort it out myself - I did the latter.

I took the carbs off, and meticulously stripped and checked each one, soaked the parts, etc. I realised the main jet in one was completely blocked - to look at it you would have thought it was a plug not a jet! I only knew it was supposed to have a hole in it by comparison to the others. The "expert" mechanic had completely missed this.

After clearing this and getting everything else scrupulously clean, all float levels correct, carbs back on and linkage aligned, etc. it ran like a dream.

I'm afraid I don't trust experts just because they say that's what they are. I'll take their advice and poach their experience, but IME if you want a job done well you usually have to do it yourself.

Cheers, Rick

[Craig LaForce]

I've been thinking some more and even resorted to reading the service manual a bit.

It warns that the CD unit needs to be unhooked to prevent damage if doing a compression test with the plugs all removed. I think you mentioned a compression test was done. So might be worth checking the CD unit. There is a table of resistances that can be checked across the 4 CD terminals

Red+ to black - 80 ohms
Red+ to white- 16 ohms
Red+ to yellow- 16 ohms
WHite + to black- 16 ohms
yellow + to black - 16 ohms

All other combinations should read non conductive (infinite resistance)

I would definitely get a test light and check each plug to see if they are all firing nicely during engine loading.

A fuel problem doesn't seem to fit the symptom of running normally at low speed and then totally shutting down when load is applied.

If fuel were the problem, wouldn't the engine stumble and sputter rather than totally quitting?

However, when the engine is loaded, the inlet pressure goes up as the throttle plate is opened. the pressure at the time for the plug to fire will go up, and if there is a weakness in the CD unit, it might fail to fire at that point (higher air pressure increases spark resistance).



Would be neat if a video of the malfunction could be put on the message board somehow.

[Hardcrab]

Craig, your "weak" CD unit can be easily checked for with a simple test.

FOR TEST ONLY, close the spark plug gap to about half of required, then observe the running results. If, in fact, the engine runs "better", then more effort is called for, as you allude to.
If there is no change in performance, then one can take ignition off of the table as possible causes.

This closer spark plug gap will be seen by the coil as an easier electrical "load", and it's voltage will not have to climb as high before the gap is jumped. With this test, a "weak" ignition source can be exposed.
("Weak" is a poor descriptor, imho)

Remember, the spark plug voltage from the coil only needs to rise until the gap is jumped. Then, voltage will remain at that level until the coil is discharged. Typical voltages for new, well gapped plugs fed by good wires, is in the 3-4000 volt range. (As per a Champion seminar years ago). As the gap wears towards more open, and the electrode tip wears to a more rounded shape, the required voltage has to climb higher and higher to bridge the gap.

To me, a very lean fuel mixture is textbook perfect for the reported symptoms. Text books call it "Lean Burn Misfire"

My money is still on the fuel path.

On Edit: The CD warning refers to not allowing the coil to discharge at all. For the compression tests or any other spark test, just make sure that a spark gap will be jumped or the plug wire is shorted directly to ground with a jumper clip, and all will be well.

[Kelly Hanson East]

EFI blows, but carbs SUCK!!

[Craig LaForce]

Mr. Crab,

You might be right. Just need to test each avenue until it is diagnosed.

Fuel is a much more common problem, but I assume there was a problem before the carb. job was done, or else why do it? Seems like they have gone over the fuel system rather thoroughly, and the problem seems unaffected.

Another test would be to visually inspect the spark plugs . Are they dry looking (supporting lean burn) or all oily and gunky (supporting misfire)?

And where are those test-light results?

Number 13, your fired. (obscure House humor reference).

[kmclemore]

EFI blows, but carbs SUCK!!

I thought it was turbochargers that blow, carbs that suck, and injectors that drip?