Mercury 150hp Low Power Engine

[Themanofsteel]

I have a 1983 Mercury 150hp. I can’t get it to go faster than 10mph. The prop is fine. Not spun.

When I throttle, it revs up, it sputters a little bit, but eventually dies. It struggles to restart after it dies.

If it only runs at 10mph its fine. Starts and goes fine. If I try to go any faster I have that power issue.

Possible issues?

FYI This engine was transplanted from another boat. I never ran it on the previous boat but it has had this issue since the first time I ran it on my boat.

 

[jimmbo]

Go thru the basics, Compression, spark, fuel. Timing advancing? carbs opening fully? throttle cables properly adjusted? Fuel lines good, no air leaks? Tank venting properly, and is the fuel pump supplying enough fuel at proper pressure?

 

[Chris1956]

Those motors also have a separate high speed stator. If the compression and other tests check out, ohm out the stator winding.

 

[Themanofsteel]

Compression is good. Spark is good. Fuel flow is good. Fuel pump is fine. Throttle cables are properly adjusted. Haven’t checked carbs yet. Not sure how to test the timing.

A couple of yellow wires coming from the Stator were in pretty bad shape. The wires were completely exposed. The insulation was brittle and came off all the way up to the stator. I replaced the wires.

Chris1956 Where is the high speed stator? Can you point out in the attached diagram pic.

 

[Chris1956]

The blue wire on each switchbox, is low speed stator winding. The red wire on each switchbox is the high speed stator winding. Test them to ground.

I do not seem to have the ohm spec for the stator windings, as they want you to use a DVA..

Obviously if they are open or shorted, they are bad.

 

[Themanofsteel]

Water was dribbling out from the red circle in the pic. Is that normal?

 

[Dukedog]

no.. needs ta have new "kit" installed.. probably leaky diaphragm..

 

[Themanofsteel]

What is the part it’s leaking from?

 

[Dukedog]

usually diaphragm.. but not always.. why ya need a complete poppet kit.. not that expensive..

 

[Chris1956]

Make sure you get the correct poppit kit for your year motor. Merc changed the design a few times.

 

[Themanofsteel]

Chris1956 What does this area on the engine do? How could it affect my engine?

 

[Themanofsteel]

The reason I ask is because when I throttle, the engine eventually starts to overheat. Could this be related to the popper vavlue?

 

[Themanofsteel]

So when I was testing the sparks again I discovered that the spark on 2,3,6, ie the left side, were slightly weaker when I throttle high. They go really faint. The spark on 1,3,5 are strong consistently. See Pic. The pic doesn't show result from all three cylinders but I tested all and the results are the same on each, 2,3,6 weak, 1,3,5 strong.

I figured this is the issue I've been having with bogging.

It's either the stator or the CDI Switch Box Right?

 

[jimmbo]

Check all the connections on the switchboxes, inspect the wires going to the switchboxes for damage.

 

[Chris1956]

If the poppit is bad, the motor could overheat at higher RPM, since the poppit is designed to allow more cooling water at high RPM.

 

[Themanofsteel]

jimmbo all the connections are good.

 

[Themanofsteel]

jimmbo Wire connections are solid from the stator to the switch box. I can't speak for the integrity of the wiring inside all the wires but visually they look good. I did expose 1 wire to see, and it look really good. The insulation is thick and the wire inside is pretty thin like maybe a 20 gauge wire. There are no breaks in the wires.

How can I go about testing the switch box and wiring? Also, what’s the likelihood it’s the stator or the trigger?

 

[jimmbo]

http://www.cdielectronics.com/troubleshootingguide/

Download and save the pdf file for future reference

 

[Faztbullet]

Just swap the red/blue leads on switchboxes and see if problem swaps side. If it does its a bad stator if not it a bad capacitor in switchbox and box needs replaced

 

[Themanofsteel]

Faztbullet Don’t know why I didn’t think of that. Looks like one of the switch boxes is bad. The problem reversed when I switched the wires. Thx Faztbullet