1980'ish black max 150 losing all power after running for 30 minutes

[cmw1]

Hi all,
I have a 1980'ish black max 150 that runs decent at idle and runs very well at high speed, for about 25-30 minutes (sometimes less). When it goes to die it acts like the fuel is being slowly cut off and it Boggs its self out. I can squeeze the bulb and it will start back up after a few seconds and will run rough until I let it sit for a while. Any suggestions or help would be great...I can take anything apart and work on it but I have a very rough understanding of boat motors

 

[jimmbo]

I suspect an Ignition Issue, due to Heat, possibly Corrosion. Verify that all Connections are clean, and secure. Switchboxes in the 80s Engines were Prone to Failure from Heat.
However, a Fuel Starvation can produce similar Action. A collapsed Primer Bulb happens when the Tank isn't venting. Try running with the Fuel Cap loose/off.

 

[cmw1]

I suspect an Ignition Issue, due to Heat, possibly Corrosion. Verify that all Connections are clean, and secure. Switchboxes in the 80s Engines were Prone to Failure from Heat.
However, a Fuel Starvation can produce similar Action. A collapsed Primer Bulb happens when the Tank isn't venting. Try running with the Fuel Cap loose/off.

So I took a look at the switch box and it seemed to be fine. I've read that these motors were notorious for having the stator go out after heating up. Not sure how to check that without just replacing it (which i dont want to do if it isn't necessary). I took the cap off the fuel tank when the bulb collapsed and it didn't seem to make a difference so I am leaning towards an electric issue....do you know a good place to find a wiring diagram. Stamp on motor claims its a 1981 mercury black max 150, serial number 5904448.

 

[flashback]

Are you getting good water flow, might be water pump failure.

 

[Chris1956]

If the primer bulb collapses, it will starve the engine of fuel, which can damage the engine.

Put a hair dryer's hot air on the switchboxes and run her on a flusher. See if it dies. If not, the switchboxes are good.

Just so you know, that motor will continue to run even if overheat is detected.

Maybe you could run the motor with the cowling off and connect a voltmeter to the stator wires at the switchboxes. Read the voltage and then run her until she dies, monitoring the voltages.

 

[jimmbo]

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[cyclops222]

Squeezing the primer bulb affected the running engine. Go after a dying fuel pump. Ignition is O K.

 

[Dukedog]

Squeezing the primer bulb affected the running engine. Go after a dying fuel pump. Ignition is O K.

 

[cmw1]

Just an update...ran rhe motor again this weekend and had much better luck as long as i drove mostly in a straight line....forgot to mention this happens mostly when pulling a tube and making sharp turns

 

[cyclops222]

Fuel pump test.

 

[flashback]

Fuel pump test.

or it ain't got no gas.

 

[cyclops222]

Mine took me a while to figure out. Car had same symptoms 68 years ago.

 

[jimmbo]

Check the Float Levels, and Volume of Fuel Delivery

 

[Chris1956]

Loses power when you turn? Sounds electrical. What shape is the wiring in? Are there any wires rubbing on metal, when you turn?

 

[jimmbo]

I guess the main Electrical Harness could be flexing/twisting when Motor is being steered

 

[Mc Tool]

Blockage between tank outlet (filter?) and primer bulb ? . Is there a filter at the tank outlet ?

 

[racerone]

Test run with a portable tank and a good hose !

 

[cyclops222]

I really dislike black rubber or plastic fuel lines.
And buildup of GOOK is unnoticed. Especially small diameter sizes. Under 3/8" size. I replace them at about 5 years.