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Merc 150 2 stroke carb - Possible control box issue?

L

Luc Perreau

Member
Hi, i am having this problem with my 150HP 2 stroke Mercury carburetor engine.

The serial number is: 0D167071

The engine starts and all 6 cylinders have sparks when tested, however, when the boat starts to accelerate and gets over 2000rpm, the engine cuts off. I don't have a DVA adapter so if possible, i would need other ways to troubleshoot.

I checked all ground connections and re-wired the switch box properly. Carburetors have been cleaned. I checked fuel pump visually and it looks good, but i am still not confident with it. I may need to buy a kit and see what happens.

May i have some assistance on how to fix this issue?

Thanks.
 
"engine cuts off"

So it completely dies (stalls right out, quits running) or it starts to hitch, slow down?

Is it you think it's losing spark above 2000 or do you figure it's possibly a fuel issue??

I have an idea or two but need a better description of exactly what is happening.
 
The engine quits running and i have to start it again, if i floor it and pull back quickly before it turns off, it stays on but under 2000 rpm. I cannot confirm if it loses spark or has fuel....that the problem. I think i am going to buy a fuel pump rebuild kit tomorrow just to make sure this is OK.
 
Yes, could be a fuel issue - a fuel pump rebuild and cleaning the carbs is never a waste. Take it from there...
 
Been there myself (messed with timing that is for a band-aid fix while on the water).

You may have a fuel issue, so like I mentioned, it's never bad to clean the carbs (maybe some new gaskets and jets/needle valves if they look bad) - plus do the fuel pump. These things get worn out and if it's original or been "many years" since they were done it's never a waste.

Along with that the motor should be timed. It normally won't go out of sync on it's own, but if any adjustment has been messed with it certainly is worth checking and correcting if necessary.

Once you have ruled out a fuel issue, if the problem persists, then you move on to other trouble shooting.

Normally, if I get a motor that is "not running right" I check the following, roughly in this order:

Compression test
Spark check
Inspect the sparkplugs
Fuel flow test
Resistance checks of various ignition components
DVA tests if resistance tests show potential issue
 
Compression test-Done (100psi on all 6 cylinders)
Spark check-Done
Inspect the sparkplugs-Done, Brand new ones being used
Fuel flow test-?
Resistance checks of various ignition components-Not done yet
DVA tests if resistance tests show potential issue-Not done yet

I will give feedback tomorrow.

Thanks.
 
Fuel flow -

in the case of a carb model you can do a vacuum test at idle speed to see if it's pulling enough fuel.

On EFI models you can measure the fuel flow from the VST on "key up".
 
Hi guys. The boat is running well now :D

I saw that the timing adjustment screw still was clean in the area where i moved it as opposed to the accumulated dirt on the other bits where the timing was set before.

However, even if i did this, the engine still shut down when i opened throttle. I then disconnected the ground of the control box and i was able to plane but i did not apply full throttle as advised by my mechanic. He said if i disconnect this box, i will need to change my timing? What timing should i use without this box and is it advisable to run my engine without this box? What will i be losing out? The box i am referring to is below.

control box.jpg
 
That would be the " idle speed stabilyzer " used to obtain smoother idle.------The dealer would have a service bulletin on what to do when it is removed.
 
You may just be running lean on the low speed jets.-----Have you tried opening low speed jets ( if equipped ) about 1/8 turn at a time to see if bogging goes away ?
 
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