2003 Mercury 150hp 2 stroke. Idles fine until rough shake/bounce at 2800rpm

[AnthonyVig]

Hello All,

I have a 2003 Mercury 150hp 2 stroke outboard that has approximately 210 hours on it. It has been meticulously maintained ever since 2003 with its last tune up in June of 2019 where we replaced:

water pump kit impeller
primer bulb
in line fuel filter
thermostat kit (2)
fuel pump kit
spark plugs
water separator
lower gear lube
poppet valve
fuel engine filter

After this maintenance the boat was fogged for storage and sat in our lift. Fast forward to June 2020, we started the boat right up and she ran great for about 5-8 hours worth of running.

Now the boat idles properly and is smooth up until about 2800 rpm when the motor begins to shake/bounce and I don't seem to have a whole lot of power. If I push through 3000-4000 rpm where most of the shaking happens I can get the boat up to about 5100 rpm ~30mph planed off but it still has some roughness.

So far since this issue I have changed the spark plugs and ran SeaFoam shock treatment through a separate 3 gallon gas tank. Also sprayed SeaFoam into the carb throats. The coils appear to be ok as well.

Up until this year, the boat was really not ran that often and is often ran at a low rpm just putting around. I understand now that thats a big no no for 2 strokes and there might be some carbon buildup.

Anyone else have this issue? Thank you!

 

[Ogerjohn]

I am having a similar issue with the same engine as you. My rpms bounce somewhere between 2800 to 4600 but seems to run fine at WOT and gets to 5200 rpm. Which is about 200 lower than I remember getting to, but seems to make my top speed on the water. I changed the plugs. I ran it for a time at my cruise speed of 4400 rpms where it was surging and shut the engine off.I pulled the plugs and found that a few plugs were a little carboned up, primarily #1 was the worst. The last time I ran the boat I idled and ran at non surging RPMs and all the plugs were clean. It’s seems to be getting good fuel, so I am leaning toward an ignition is an issue. I checked the resistance of the stator and was in spec. But I did find that the resistance of One of the trigger coils is low, out of spec. It is the one that I believe is for the #1 CDM, as long as mercury follows the same color from the trigger through the module to the CDM. Right now I have a trigger on order and won’t know if it works until next weekend. I did have a bad filter a few years ago that was a result of the ethanol eating the liner of my fuel line and clogged the fuel filter.

 

[AnthonyVig]

My mechanic believes this issue lies with my control module (857185t1 / 857185a1). I just got a new one today and am going to try it out tomorrow. Did you solve your issue with a new trigger?

 

[QBhoy]

If this is an optimax, it’s not a great idea to run fogging oil through it really.

 

[Texasmark]

Hello All,

I have a 2003 Mercury 150hp 2 stroke outboard that has approximately 210 hours on it. It has been meticulously maintained ever since 2003 with its last tune up in June of 2019 where we replaced:

water pump kit impeller
primer bulb
in line fuel filter
thermostat kit (2)
fuel pump kit
spark plugs
water separator
lower gear lube
poppet valve
fuel engine filter

After this maintenance the boat was fogged for storage and sat in our lift. Fast forward to June 2020, we started the boat right up and she ran great for about 5-8 hours worth of running.

Now the boat idles properly and is smooth up until about 2800 rpm when the motor begins to shake/bounce and I don't seem to have a whole lot of power. If I push through 3000-4000 rpm where most of the shaking happens I can get the boat up to about 5100 rpm ~30mph planed off but it still has some roughness.

So far since this issue I have changed the spark plugs and ran SeaFoam shock treatment through a separate 3 gallon gas tank. Also sprayed SeaFoam into the carb throats. The coils appear to be ok as well.

Up until this year, the boat was really not ran that often and is often ran at a low rpm just putting around. I understand now that thats a big no no for 2 strokes and there might be some carbon buildup.

Anyone else have this issue? Thank you!

Was going to help till I saw the word Optimax. I accidentally obtained a manual on one and I have no business answering questions on that engine. Compared to my same year carb engines, way out of my ball park.

 

[AnthonyVig]

Hey all, the motor is not an optimax. Installed the new control module and she’s still having the issue. Going to use a timing light on the plugs this tuesday and do some more troubleshooting.

 

[Texasmark]

Hey all, the motor is not an optimax. Installed the new control module and she’s still having the issue. Going to use a timing light on the plugs this tuesday and do some more troubleshooting.

Okayeeeee back in the game. The "Decarb" procedure recommends replacing the plugs AFTER the treatment and the engine has quit smoking. Pull your plugs and check for fouling, or just replace them...not that big of an expense.

With what you said, before you spend a lot of money chasing possibly a ghost, I'd (what I would do if it were my engine) would be to add 2 oz per gallon vs the recommended 1 oz per gallon (on the can) for a couple of tanks of fuel....assume 20+ total gallons of fuel...at least, and give the SF time to clean up any carbon and give your engine time to wear in a little better. Then if things aren't running right come back and tell us how it went.....ask more questions if not happy.

 

[AnthonyVig]

Will do. Thank you!

 

[Ogerjohn]

The Trigger did fix my issue. I never realized that my engine had not been right for a while. The out of spec coil in the trigger must have just been timing it off. It runs much smoother now through the upper RPM and sounds the same at idle.

 

[AnthonyVig]

Alright problem resolved. I had 3 issues all at once.

1st issue While under load we one by one tested each cylinder by pulling the coils off at different RPMs and found that I had a bad coil on the top left cylinder (if you are viewing motor from rear). Replaced coil all is well.

2nd issues was the primer ball was soft and faulty which is odd because it had less than 10 hours of use but had been sitting for 12-13 months.

3rd issue was that when you picked primer ball up to prime engine a kink developed on the fuel line coming out of the water separator mount.

By all means, I am NO mechanic but learned a **** ton these past couple weeks. Thanks all for the help.