Re: 20HP Mercury "Surging"
As a last resort......you might have a high voltage leak in one of the coils or leads. This will occur as the engine speeds up and the coil voltage increases, thus the intermittant sputtering at high speed when the voltage is the highest. To check exposed hightension wires, run the engine at nite in total darknes and look for fire flies with the cover off the engine. For the coils themselves, you have to check under load in the water by pulling one of the wires off when running WOT as soon as it starts to sputter....careful, this is a acrobatic manuver of the body when doing this, use insulated pliers..........from there you can determine if you have a weak coil. In addition, I think the motor you have might use points. I don't remember for sure, you have the old weed angle 20 HP with the early "Thunder Bolt" ignition as I recall. If it does have points, I would check the gap and condition, and if it uses a condensor this problem will occure if you have a weak condensor. If you have no points, then it is most likely a coil problem if the fuel system has been gone thrue.<br />Aside from that, the particular engine you have was one of the best made by Merc. It will idle smoothly for hours without loading up if properly adjusted. I had one for 5 years and ran the crap out of it 3 times a week with never a problem till I sold it.....
