Tohatsu 50D - Problem not fixed yet

[hvaldezz]

I wanted to make sure this got read so I started a new thread. The parts for the fuel pump and the new fuel filter came in and were installed. Backed the boat back into the water and it idled perfectly, put it under load (prop in the water) and it died....sooner than before.

When the Tohatsu mechanic started troubleshooting and after adjusting the carbs, he could cover up the carb throat on the top one and the engine would begin to sputter, then the 2nd carb and almost no change, the 3rd carb did the same, not much change.

He now suspects that it may be a coil problem as there is one coil per cylinder....could 2 be bad?

Daylight left us and we had to pull it out of the water to try and ohm out some of the assemblies tomorrow. I'm pretty sure that it's not a couple of weak cylinders because the all measured about 135 lbs compression.

This has been a tough one and he's been in touch with the Tohatsu people in Dallas, TX and they're working the problem.

Wow, I thought I would be done by late this afternoon but Murphy's Law has come into play.

Anyone see anything wrong with his approach?

As always, any help is appreciated.

[kmclemore]

Sounds to me like you're on the right track.... let's see what the Dallas folks say.

Of course, I expect you've checked that the choke is working properly, right?

[Newell]

I wouldn't think 2 coils would fail. Besides covering the carb. it would also follow to put a timing light on each spark wire. It doesn't seem like ignition, but fuel supply to me.

Newell

[Craig LaForce]

sounds like the choke is still engaged.

It chokes 2 of the carbs IIRC.

I apologize if the following is basic stuff you already know. But in the interest of being complete...

The choke is activated 2 ways.
There is a manual choke lever on the engine itself. should be pushed in.
If you remove the plastic carb cover you can visually confirm it as open.

Also, the ignition key activates the choke electrically if you push the key in while cranking the engine. I believe this is a separate preset amount of choke. On mine it is much less than full choke with the manual lever.

I suspect the manual choke lever is either pulled out or unhooked.

The other thing to check is that all of the throttles are being moved about the same.

[Don T]

Hello,
I have to say this, your "mechanic" should know if it is a coil or not. Checking that stuff is very basic trouble shooting skill. Hey, just pull off one of the plug wires, stick a spare spark plug in it, ground it and see if it is arcing.

You can get the same effect of covering carbs = no change when they are slightly out of sync. It can mean one cylinder is pulling harder than the others so the coasting ones load up with fuel & oil.
You can squirt a bit of gas in one carb to see if the lower cylinders fire off because of fuel starvation.
Check for "pulse back" while cranking to see if the reed valves are closing.

Heck maybe you have a broken wire under the flywheel that opens the ground when the timing is advanced. It idles fine and quits when the timing plate moves.

None of these test require any special tools. Basically you are looking to verify the big three (FUEL, FIRE & COMPRESSION). That of course means Fuel in the proper ratio, fire at the proper time and functioning valves / pistons / rings. If these things are present, it runs. It's not black magic.

[BKAFER1]

How about a crack in a manifold. The carbs are set so that it idles ok.
PLace your hand over the carb with out the crack and it dies out. No air.
Place your hand over the two where the crack is, and it draws air thru the crack and still keeps running.

I'm not a boat mechanic, I used to repair lawnmowers for 6 years. Before electronic ignition. ( the good old days)

[Hardcrab]

First of all, let me say I have never worked on your type engine . But I have been paid to work on many other types, from lawn motors to military aircraft piston engines, and the basic theory is all the same, regardless.

Three carbs. Do they feed one common intake manifold or is it one carb per cylinder?
I assume it's a three cyl engine.

If one carb feeds directly for one cyl, that's the equilivent of three independent "engines" driving one crankshaft. That would mean the carbs are out of sync. A "tube style" mercury vaccum gage set, much like the one used for motorcycles, is nice to get each carb/cyl combo to pull equal weight, if you can adjust the metering jets. If not adjustable, those carbs have to come apart to find out why they are not contributing their equal weight.

If it's common manifold to all cylinders, two of the carbs are not metering fuel very well. Maybe junk stuck in the main jet or some fuel passages are clogged. Badly set float levels could do it too. They need to come apart. The one good carb can supply enough fuel for the minor idle requirements, but not enough fuel to feed everybody for much above idle.

Cracked intake manifold/ poor gasket/ vacuum line leak is possible. Any air sucked directly into the manifold is air not drawn throught the carbs, therefore has no fuel mixed with it and is a very lean mixture. Again, idle is usually not affected much, but not good results above idle. I can't imagine a vacuum line going anywhere on this engine, but check.
A good check for a crack/gasket is with a spray can of starting fluid ether. Be careful to not spray into the carb throats, just all around the manifold. The ether will be drawn into the crack, raising the idle rpms revealing any crack/gasket issue. Any ether drawn into the carb throats will give an invalid rise in rpm's.

For the coil check, I think a better, more conclusive check, would be to pull each plug wire, one at a time, while running, and see the results. Without this one cylinder now "known" not to be firing, you can better gage the effectiveness of that cylinders/ spark plug contribution. (Remember, the wire only bites you while you hold it. )
I also would bet against two coils bad.

Coils either work or they don't, much like light bulbs. I'd be more concerned for the "color" (voltage) of the spark, witnessed at a pulled spark plug and grounded to see the spark. A hot blue "snap" is required (high voltage). If it's a dull yellow color, (lower voltage) the condenser is at fault for that coil. This will cause the plug not to fire under compression. Once again, idle is not affected too much.
Of course, any pulled spark plug should not be "wet" looking, indicating not firing in the cylinder. I have seen bad spark plugs that will fire outside of the cylinder, but not once installed in the cylinder. Strange but true.

I'd do the quick "pull the plug wires one at a time" check first to eliminate, once and for all, ignition from the answer. Pre-loosen them before you start. You want to see the idle to be affected equally "badly" with each pulled wire.
Then, the only thing left to cause your problem is the carb/fuel circut.
My money is on the fuel path.

A "one cylinder acting/running" three cylinder engine would not give you much confidence to even untie the dock lines, IMHO.

I love troubleshooting engines!

Good Luck.

[Craig LaForce]

OK. Stand back people. I will engage my mighty brain and need some room, lest you all be singed. We are entering the realm of obscure possibilities. Where the boundaries of time, distance and mass become blurred. We are entering the twilight zone.

Check , (remove,clean and tighten), the wiring connections to the battery (at the battery and at the motor). A weak spark would work fine at idle when intake pressure is low, but will not fire under higher compression pressures that one would see at load. Normally this would point to a weak coil, but since each cylinder has its own personal, private coil, highly unlikely.

I now return you to your own dimension. Where the rules of politics and skeptical debate reign supreme over the laws of nature and man.

Think I might have overheated a lobe there. Need some tropical coolant elixir.

Oh, and for the love of all that is holy, please stop making new threads on the same exact topic. It makes it harder to follow the thread. There is a view new topics button on the right that will bring your post to the top of the list each time it is updated.

Thanks

[pokerrick1]

[Kelly Hanson East]

Try running the engine at night, as black as you can find, and look for sparks from the coil wire to the head/block - unless you have already replaced the ig wires....

My gut feel is fuel circuit too.

[pokerrick1]

And try running the engine at 3:02 PM - - - cause that's a good time to go sailing if the engine doesn't work

Rick

[Don T]

Hello,
FYI
Because this engine is a 2 stoke, chances are that each cylinder will not cause an equal idle speed change. The rough sputtering idle is caused by excessive exhaust gas being sucked back into the cylinder along with insufficient scavenging of fuel / oil out of the crankcase. It is normal for it to actually idle better when one spark plug wire is disconnected. The exhaust passage is filled with unburnt fuel that improves the mixture in the other two cylinders and the running pair are now under load. Because of their position in the exhaust passage and firing order, each cylinder will act differently.

There is no common manifold, the carbs feed directly to the reed valves. There is, however, a small balancing passage between the carbs and a vacuum line that connects to the fuel pump. The crankcase pulsing actvates the pump diaphragm (just like on your lawnmower).

[Craig LaForce]

I am trying to remember if he replaced the fuel pump. This thread is scattered a bit.

Mr Valdezz, how is it going? Any luck yet?

[Kelly Hanson East]

Im sticking with crap in the carbs and plugged main jets...

[Don T]

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.