Opti 150 Issue – Any thoughts?

I was pulling the kids tubing today and came off the throttle as I came into the dock and my 150 Opti shut down. I could not get it started.

I got it back to the dock and the only way I can get it to run/start is in neutral at half throttle. When it is running it sounds like it’s knocking bad. If I back off throttle it dies.

I have not had a chance to dig into it yet, but wanted to see if anyone had any thoughts on where to start. I am thinking I have a speedy repair bill coming.

– Fuses are good
– Compressor belt is good
– oil in reserve reservoir and regular reservoir is good
– No alarms
– engine is still pissing normally
– I have not replaced the fuel filter this year.
– plenty of gas. I just put 20 gallons of non-oxy in it yesterday, and have only run non-oxy in it. I have put fuel in it earlier this year, but it’s not run a ton.

Hoping it’s not a rod or bearing, but thinking this might be the case. Boats still in the water so I have not had a chance to check compression yet.

relieve the tension on the compressor belt and remove the belt.
try to spin the compressor by hand,if it is good you should be able to feel it trying to make pressure as the piston in it nears the top of the stroke.

if it feels rough or is binding when you try to turn it,it has most likely shucked its rod bearing, broke the rod or crank pin.
that motor is hard to start and wont hardly run at all if the compressor isnt working correctly.

if the compressor shucked its cookies there are filters in line with its oil drain hoses that should protect the motor,make sure you change all of them if the compressor did fail.

that compressor has been through many updates and the newer ones route the upper bearing oil supply hose differently.
I hope for your sake its that simple,good luck and post back on what is found.

I did pull the belt last night after I posted this and the compressor seems to be good. I didn’t feel any binding/grinding….it felt smooth.

Could it be battery voltage related? Doesn’t seem like it, but I don’t know if it would start at all if there was a battery issue. I read somewhere that they need more power than they generate at low RPM’s, but that doesn’t really make much sense to me.

I had alarms go off when I had voltage issues with my 150 optimax. Ended up getting a new battery and then had to switch out the alternator as well.

A quick update. I check compression (cold) and it appears I have lost cylinder #1 (plug was light as well). Not sure what caused the lean condition at this point.

Is Lyback’s still a go to service center for Mercs?

I wouldn’t go anywhere BUT Lyback’s for Merc service.

Well, the results are in. Cylinder 1 air injector tip broke off and stuck itself into the top of the piston. Lyback’s said it’s the first time they have seen that happen. They replaced the injector, removed the piece from the top of the piston and the engine runs great.

I believe he said they did a leak down test on the cylinder #1 showed it to be good. It sounds like they don’t rely on basic compression tests….he gave me an explanation but I can’t recall the rationale. So, not sure what I was seeing low compression on that cylinder….I will ask more about it when I pick the boat up.

So, this is good new to me…..I was figuring for far worse repair.

good to hear you are getting out cheaper than you thought !!

most likely the reason you were seeing low compression when you tested it is because that cylinder may have been flooded due to the bad injector allowing too much fuel into it.
the extra fuel washed the oil off of the cylinder walls and the rings couldnt seal properly.
once a flooded cylinder is firing again the compression will come back as oil is now helping the rings seal up the way they should.

leak down test,one of the most misunderstood tests on motors,I will try to explain it so that all will understand.
it is done with what is called a differential tester that has two gauges,one is regulated,the other one that has a hose with an adapter screwed into the spark plug hole “reads” what is happening in the cylinder at top dead center with the ports closed on a two stroke,or the valves closed on a four stroke.

the second gauge is telling you how much of a seal is being provided by the rings and valves and it will reflect that seal in the form of a pressure reading and you compare that with the regulated gauge.
look at this way,the first gauge is regulated at 100 psi,read this as one hundred percent.
in a perfect world,the second gauge should also read one hundred but that never happens,in a good running engine you will see anywhere from a seventy eight to ninety percent ( pounds ) reading.
purpose built race engines using gapless rings will read very close to one hundred percent.

while the cylinder is under pressure and if the second gauge is not reading very high,you listen for where the air is escaping out of the engine,ie,
air leaking into the crankcase indicates bad rings of whatever fashion or a worn bore.
air leaking out of an intake port on a four stroke indicates a faulty seal between the intake valve and its seat.
air leaking into the exhaust indicates its valve or seat is worn,more to this but you should get the jest of it.
similar air leaks on a two stroke indicate ring failure most often as they are the only seal between the piston and the ports.
to sum it up,a leak down test can tell a technician much more about the engines health than a simple compression test can.

as far as worrying about the ding in the piston,if Lyback’s says its good,then its good to go or they wouldnt risk taking the chance of having to warrant their work.