Strange Motor Behaviour.-

[Sea Rider]

With a 2 stroke motor motor sufficiently warmed up revving strong from idle to say 4-5K at neutral is it possible for any electrical component to fail ( motor will not rev up) when geared forward but run strong at max wot range once motor has passed this condition issue ? It's not a fuel related issue as everything is in excellent shape, seems pure electrical .

Happy Boating​

 

[pvanv]

Possible, but difficult to isolate unless you have spares to swap in and test. A weak spark might not show up in neutral.

 

[MattFL]

On a 2 stroke a weak spark can behave very similar to being excessively lean. If you're sure the fuel delivery side of things is OK then replace the spark plugs and start working your way back from there.

Just food for thought; as teenagers my buddy had a 150 HP mercury V6 2-stroke (back in the early 1990's, so it was probably a late 1980's motor) that behaved exactly as you describe, but it was due to the carburetors being all plugged up from sitting with old fuel. In neutral it sounded fine. In the water it felt to have almost no power until you could get the RPM's up over a couple thousand, then it would pull harder and run what felt to be more normal. We were stupid teenagers so for a while we would just trim the motor until the prop slipped, allowing the RPM's to climb at which time we would trim back down and take off. Eventually the carburetors got a rebuild and it was a whole different motor and ran great bottom to top, and we realized that what felt to be normal up top with the dirty carburetors was really less than 50%. It was a 16' bass boat with 150HP that we took everywhere including the ocean, because we were stupid kids. That boat would fly, it was a miracle we survived it. We did find out that the marine patrol does not consider 65+mph with "no wake" to be the proper way to handle a no wake zone. That was a different era, kids today wouldn't be able to get away with half the things we did back then. One day we went to use the boat and it was gone, his dad had sold it without warning. Probably because he figured out what we were up to.

 

[Sea Rider]

Ohm and DVA testing while pulling the rope won't say much when having repetitive erratic electrical component failures during operation under load. Swapping new electrical components one at a time it's the fastest way to troubleshoot, luckily have all 3 of them, will start with a new Ignition Coil and check what happens...

Happy Boating​

 

[Faztbullet]

What kind and HP engine?

 

[Sea Rider]

What kind and HP engine?

2 stroke Tohatsu 30 HP with over 700 metered worked hours...​

 

[dwco5051]

Not to hijack you question but I have a 1987 30a3 right now with a similar problem. Idles well, runs great flat out, but surges back and forth a couple of hundred rpms in between. What I have done so far this Winter.
Checked link and sync, it is spot on.
Installed a tach so when the ice is out I can check things on the water.
Went over every wire connection for loose connections.

This motor is very low hour and had not been run for 3 or 4 years but looks like in came from the showroom. The gas tank was disconnected was dry and clean. I was told by the previous owner (deceased) neighbors he was almost a fanatic about his boat. I did forget to check the float bowl when I first ran it and don't know if there was gas in it when he put it away for the last time.
I did put a wrench on the carb to engine bolts just to see how hard it was going to be to remove and discovered I could get almost a full turn to tighten them. I have no idea why that was unless the gasket dried out and shrunk. I suspect perhaps one of the jets may be clogged but am putting off rebuilding the carb until a water test with an accurate tach and playing with different trim positions.
I will let you know if I find the solution.

 

[Sea Rider]

Don't worry Dwco, tear the carb and clean all the jets, nozzles, float's valve seat, micropolish it if too dirty. Spray carb clean spray in all air and fuel passages, don't need a carb kit everything inside its cleanable to perfection so save the money.

The strange motor behavior with this 30 points out to a faulty Ignition Coil, the motor lost 250/300 wot rpm on last wot test when used to rev to its full 5850 wot rpm range as loaded. Have discovered through my boating years that no electrical component is eternal, will eventually fail over use and time. Sometimes boaters gives too much concern being fuel related issues to discover lately that was an electrical issue.

Happy Boating​

 

[Faztbullet]

The strange motor behavior with this 30 points out to a faulty Ignition Coil, the motor lost 250/300 wot rpm on last wot test

Explain your theory/testing on above........

 

[Sea Rider]

Explain your theory/testing on above........

No theory whatsoever, the wot rpm reduction is what dual installed tachs indicated under practice and 2 can't read wrong or way off. My guess is a gradual power loss on the Ignition Coil due to extensive use. Can run the motor at neutral at any rpm range all day long with 0 issues. If being a CDI or exciter coil related the motor would definitely misbehave when running at fast idle to wot rpm range and that's not happening.

Happy Boating​

 

[racerone]

Running a motor wide open in neutral is a mistake.------And a 2 cylinder motor will sound wonderful at full throttle on just one cylinder !!----Means nothing.

 

[Sea Rider]

Running a motor wide open in neutral is a mistake.------And a 2 cylinder motor will sound wonderful at full throttle on just one cylinder !!----Means nothing.

Who said liked running that way ? It's not only a Huge mistake, it's Insane to run any motor at wot at neutral without load. A 2 stroke 2 cylinder Tohatsu motor will not run even nor sound happily when running at full throttle on just one cylinder. Such scenario will match a 3 cylinder motor running with just 2 cylinders...

Happy Boating​

 

[Faztbullet]

Your tachs are off...you have 2 cylinders connected to crankshaft. If top cylinder reads 5000 RPM the bottom cylinder is moving at 5000 RPM, there is no way a cylinder can have lower RPM than the other.

 

[ahicks]

So what is your issue, exactly? Are you saying you lost 2-300 rpm on a wide open run as compared to the last time you checked?

You said earlier you were going to change a coil to see if that helps. Have you done that yet?

And 700 hours is nothing on an outboard. Most given just decent care, will go several times that....

 

[Sea Rider]

Being this 30 HP a sinle carbed motor with a dual ignition coil you can connect an induction tach at any of both spark plug's cables, both will read the same wot rpm, sorry you're late, gun powder has been already discovered. If the tachs were way off moons back would have blown my Club's, friend's and my motors in pieces. All of them have installed tachs and runs maximized props to rev towards their respective max wot rpm ranges and slight over while pushing near fixed loads.

This is the real scenario better explained : . With fully warmed motor when the lever is put in forward operation at 1/2 throttle the motor will go br, br, br, if left at that fixed throttle position will clear itself in a few seconds and motor will rev up with no extra issues.

When goes br, br at 1/2 throttle, if applying more throtte the continued br, br will change dramatically to an eternal brrrrrrrrrrr,brrrrrrrr that motor won't clear. Have tested the motor with a new thermo installed and without it, same issues at both scenarios.

If the motor is run at full throttle for 1/2 hour and then come to a 2-3 min idle stop will begin doing that. Have retorqued the whole powerhead to specs with no avail. Tomarrow will test with a new ignition coil, hope i's the culprit and not a costly CDI. As said earlier electric components are not eternal and acccording to my experience an ignition coil will fail earlier than any other electrical component, doesn't matter if having a mint motor well cared for...

Happy Boating​

 

[pvanv]

Yes. Those CDs are very rugged, and coils are cheaper, so if swapping to test, I would also do the coil first.

 

[Faztbullet]

Take a timing light to the coil, when it br,br,br gheck to see if it double firing a cylinder or firing late. If so its either a pulser of CDI...seen this problem on Merc 4 cylinders and bad bias reference from trigger

 

[Sea Rider]

That's the worst slow testing procedure going for when you already count with all the electrical components to swap and test. Nope this M30A4 doesn't use a Pulser Coil. A CDI is the last component that would like to find shot, it's a real expensive component compared to a way cheaper Ignition Coil. Let's see what's found today...

Happy Boating​

 

[Sea Rider]

And the culprit (drumroll) wasn't the Ignition Coil, with a new one installed the br, b, br has lessened a bit more and the motor has gained + 100 wot rpm than last water test. But after a long wot run when throttling to neutral/idle will start doing immediately same. Will install a new CDI in and call a witch doctor and check...

Happy Boating​

 

[jhande]

I worked for many years as an auto tech and I must say, swapping parts until you find the culprit is a definite redneck backyard way of fixing things which can be quiet costly.

Electrical issues: follow the circuit from either end and test each component as you go along. Such as ignition, I like starting at the spark plug investigating the tell-tale signs. Following back and testing the wires, distributor (if it has one) the coil(s), etc...

Basic coil testing:

More detailed:

How to test CDI ignition: