tohatsu m50d misfires at cruise

[nautiquetroy]

I have a 50 hp tohatsu mid 90's and the engine has 120 lbs compression in all 3 cylinders and idles and runs out fine, problem is that at 3/4 throttle the engine runs good for about 5 mins and then drops a cylinder until I back down to 1/4 throttle and then runs fine back at 3/4 throttle for another 4 or 5 minutes with the same result of one cyclinder dropping off. I cleaned the fuel line connection to the engine. I assume this sounds like fuel, haven't checked the fuel pump or screen (if there is one). its running off a portable tank, vent is open, pretty sure theres no water in the tank. Any ideas on problem?

 

[TOHATSU GURU]

Re: tohatsu m50d misfires at cruise

You need to check and see if you are losing fire to one of the plugs when the engine drops RPM.

 

[nautiquetroy]

Re: tohatsu m50d misfires at cruise

what is the best way to do this under way?

 

[TOHATSU GURU]

Re: tohatsu m50d misfires at cruise

There are two methods:

1) Get someone you don't like to hang over the engine and manually pull the spark plug wires off while underway and having the malfunction. The benefit to this method is the potential injury to that person and then you can claim that you didn't know any better.

2) Inline spark indicators available from any auto parts store. I use this method myself as I have elimated enough people in my life as it is and don't need those pesky survivor lawsuits.

 

[nautiquetroy]

Re: tohatsu m50d misfires at cruise

Excellent!! I will either get my brother inlaw to help or stop by the auto parts store and pick up 3 of these jewels. thanks so much for your help. lets say there is one cylinder that looses spark, what then might that problem be as it recovers the spark quickly and easily by just backing down on the throttle for 5 to 10 seconds?

 

[TOHATSU GURU]

Re: tohatsu m50d misfires at cruise

It could be A N Y T H I N G, but the two most likely would be an ignition coil or a trigger assembly. You can backyard mechanic the coil test by just swapping a coil off of another cylinder. The trigger would require you to have a ten dollar ohm meter, the knowledge to use it and a service manual to give you the test procedure. The CD module could also be fail on one cylinder and not another, but that kind of failure is rare.

 

[26x]

Re: tohatsu m50d misfires at cruise

So Troy did you ever find the problem? I think I have the same thing happening..

I'm going to take the boat to the mechanic today but he says he can't get Tohatsu parts so doesn't really work on these motors and is very limited as to what he can repair.

Aside: Elvin do you know where I can buy parts for my Tohatsu M50DEPTO in the Western United States region, or anywhere for that matter? My biggest fear is I may have possibly threw a rod (as thats what it sounds like at high rpm) and will need parts for my mechanic to repair? At teh very least will need a coil right? :redface:

TIA

 

[TOHATSU GURU]

Re: tohatsu m50d misfires at cruise

Anyone of the 300 plus dealers in the western U.S...Or one of the additional 700 in the rest of the U.S. You can use the dealer locater at tohatsu.com to find the closest one to you. Throwing a rod is so rare as to not be a possibility. A coil failure is possible, but you have to troubleshoot the engine and eliminate each possible cause before you start replacing parts.

 

[26x]

Re: tohatsu m50d misfires at cruise

Thanks TG.

Now I'm wondering about my mechanic? Parts come from the DC in Texas. No big deal....

I bought the service manual and I was trying to time the ignition on my D50 but the book does not say what exactly the timing mark is.

Do you have any idea? Is it the leading edge of the magnet on the flywheel?
I looked at that and it is 90 degrees off so i was thinking that cannot be it. I spent all day reading the entire manual and am frustrated with this. I did learn alot but there still are some things not showing like what the timing mark is. Any ideas?

Also I need to check a couple coils with a voltage "peak meter" Don't know what this is and they don't sell it at the auto store.....

Thanks for any help you can give me.

 

[TOHATSU GURU]

Re: tohatsu m50d misfires at cruise

The engine is timed by measuring the link adjustment arms and adjusting as necessary. A "peak voltage meter" is meter that measures "peak voltage". Try a bigger auto parts store...NAPA or just do a search on the net.

 

[26x]

Re: tohatsu m50d misfires at cruise

The engine is timed by measuring the link adjustment arms and adjusting as necessary.

TG, I've done that. Doesn't that just get me in the ball park?

How do I fine tune the timing? I thought I would use an automotive timing light. At least it showed one at the beginning of the chapter. Then it went on to say "make sure the timing mark is at 3 degrees. Only problem is it doesn't say exactly what the timing mark is.....

In revving the motor up a bit it seems to be missing and sounds slightly retarded.

 

[TOHATSU GURU]

Re: tohatsu m50d misfires at cruise

You don't need or use a timing light on this model. It's measurement only. If you have the measurements right then the engine is timed. One warning though. There is a 50 D and a 50 D 2. Different measurements. Make sure you use the right one for your model. If you are using a doorstop manual it might not have the one for your model in it.

 

[Sea Rider]

Re: tohatsu m50d misfires at cruise

TG, I've done that. Doesn't that just get me in the ball park?

How do I fine tune the timing? I thought I would use an automotive timing light. At least it showed one at the beginning of the chapter. Then it went on to say "make sure the timing mark is at 3 degrees. Only problem is it doesn't say exactly what the timing mark is.....

In revving the motor up a bit it seems to be missing and sounds slightly retarded.

Does your engine have timing marks like these ? Have a pic look. Look under the flywheel.

 

[26x]

Re: tohatsu m50d misfires at cruise

Does your engine have timing marks like these ? Have a pic look. Look under the flywheel.

Yes.