Merc v-6 150 blackmax (electrical?)

[LaGaviota]

I tried to solve this issue last summer by myself and failed. my engine some times runs at 5200rpm and then drops to much lower rpm at WOT. it will drop to various lower rpms...sometimes 3000rpm and sometimes 2200rpm and even lower. it ran for a while at 4000rpm...its all over the place. the master merc mechanic at Port Harbor Marine in Raymond, Maine couldn't figure it out last fall and he will get one more try as soon as the ice melts (3weeks). he replaced the trigger already. he said that it looks like there is a hairline crack in a magnet on the flywheel...could this be the issue? it is NOT the carbs and jets...they are as clean as a whistle and the mechanic set the floats. any thoughts?

 

[Laddies]

Re: Merc v-6 150 blackmax (electrical?)

There are a few thing that could cause the problem, all easily tested by a competent mechanic with a DVA meter, a shorted rectifier will cause the stator to heat and break down, of course a bad stator can lose one side and the engine will run on one bank, the bios in the switch boxes can short causing a problem and of course a switch box. To test for the type of problem you have you need a serviceman that understands the system alway ask the man doing the repairs to explain how the system works if he can't or trys to baffle you with BS find another service place. He also needs to have a DVA type meter and know how to use it, you usually can't find intermittent problems with a OHM meter and the systems parts are expensive, you don't need a parts changer telling you this part that I just change was bad but I think it burned out this other part which in turn must have burned this other one out maybe we should put ever thing new on so it will be reliable again.

 

[jims3000]

Re: Merc v-6 150 blackmax (electrical?)

i had a simular problem and i was useing alot of gas never seen any fuel leaks while running.it would run fine one minute and then it would fall on its face.i ckd everything electrical then the last thing i done was removed the carbs and the top one had the needle seat come loose and the cylinder would flood out sometime and then run fine the next.tightend it up and took it back out ran just fine.

 

[j_martin]

Re: Merc v-6 150 blackmax (electrical?)

I'm with Laddies. First thing you need to do is determine for sure if it's electrical or fuel.

Then you have to figure out where it's weak, thus the DVA. The cost of a DVA will be paid back with only one typical service call, so it's worth while to get one or make one.

Swapping parts is costly, unless you have a lot of used parts laying around to play with.

hope it helps
John