1979 Mercury V-200 "Surging" While On Plane

[tdwelch]

I have a 1979 Mercury V-200 on a 20' Bass Boat. It had been sitting for a couple years when I got it. I had to rebuild carbs, fuel pump, replace stator and a few other things. It starts, idles and runs great for the most part. There is one thing I cannot seem to figure out. It seems to "surge" 100-200 rpms while on plane. It does this at various rpm settings. It will just jump up 100-200 rpms from where you have it set and run like that for a few seconds and return to the original setting. It doesn't sound or feel like it is missing, just a temporary surge up in rpms. I have racked my brain trying to figure out what is causing this. Any suggestions would be appreciated.

 

[CharlieB]

Re: 1979 Mercury V-200 "Surging" While On Plane

Does this motor have an 'idle stabilizer' on it? A little black box connected to the white Bias wires of the switchboxes. If so remove it, drop it over the side to see if it floats.

Check WOT timing cranking, reset to 23 degrees.

An idle stabilizer is 'supposed' to add or take out a couple degrees timing to help 'stabilize' idle speed. When it goes bad, it starts adding or taking out timing whenever it wants, often advancing too much at WOT and destroying the motor. Get rid of it.

 

[tdwelch]

Re: 1979 Mercury V-200 "Surging" While On Plane

The idle stabilizer has already been removed. Could there be something wrong with the trigger assembly, causing the timing to fluctuate when its not supposed to? I have also noticed that there is a few seconds hesitation when I try to come out of the hole. Hesitation may not be the right word. It seems like it takes a couple seconds to "wind up", maybe the timing is not being advanced immediately.

 

[j_martin]

Re: 1979 Mercury V-200 "Surging" While On Plane

If you suspect timing, check the trigger for mechanical freedom. I've seen some goofy things happen when the harness from it is strapped down anywhere but one strap on the side hold of the switchbox mounting plate. Harness from trigger has to be on the top of the heap so it's free to move also.

Sounds to me like you're dropping a cylinder intermittently.

First thing I would do is detail clean and check all the connections to the switchboxes, including the ground straps.

By check, I mean tug on the terminals gently to be sure they aren't loose.

After that it's DVA time.