Problem with 150 HP merc Black max v-6

[Lew]

My friend has a black max 150 that recently burn't out the switch boxes and rectifier. All was replaced with new parts. Good strong spark (1/2 inch or more on spark testor) and timing is correct. Rebuilt the fuel pump (why not we were bored) and all seems well with the carbs. Motor will idle OK then at about 3000 RPM underload it breaks down and runs rough.

Our next direction is to go into the carbs and check for problems.

Did check the bowls and the jets are clean.

Compression is 120 PSI and even.

[Lew]

I forgot to add tha tthis is a 1986 motor

[KURAN]

get new trigger sir, that most probably the matter because engine learnt performed well below 3000 rpm

[Lew]

Thanks Kuran for your reply.

My friend did check the resistance on the coils of the trigger. There was no sign of trouble but this does not mean that under performance it may be breaking down.
Thanks Lew

[Lew]

We have replaced the switch boxes, rectifier, triggers, rebuilt the carbs, the fuel filter, checked the compression (120 and even) and we still cannot get this engine to go over about 1800 RPM without bogging down under load.Timing is good excellant spark and all seems correct.

Anyone have any ideas?

[Lew]

I talked with a Mercury service department and he told me that in our area (Boston)That MTBE a gas additive was recently replaced with ethanol.
This has been causing problems with many (new and old) engines due to water and reacction to any MTBE left in the system. There is a product called Startron which will cure this problem. Startron is flying off the shelfs here and is in short supply.

What happens is the high speed jet gets cloggged with the water/ethanol mix which floats in the gas rather than sinks. Dry gas will not work.
We will try it and see what happens.

[Lew]

Success !

Turned out to be the stator was bad.

We have surmised that the rectifier failed sending AC power into all of the areas working on DC power and cause a total failure of all of the connected electrical components.

Boat is skimming along at full speed of 50 MPH.

Total cost about $500.00.

We figure if you see your tachometer failing suspect the stator. Also check the voltage going to the switch boxes from the stator. The fastor your engine turns the voltage should go up.