1985 Mercury, 35 hp, Cold Start

[ericick2003]

My 1985 Mercury, 2 cylinder, 35 hp OB engine is usually very hard to cold start (90%). It also sometimes stalls when idling hot(5%). It occasionally is hard to hot start (10%). BOTH plugs partially foul after 1 tank (6 gallons) of gas, correct 50:1 mix; cleaning them brite assists cold starting. I suspect the ignition system, but have not started any testing. I suspect the ignition coils... but am curious as to what the function of the "switchbox" is in the ignition system (per the schematic, it takes electrical input from the stator and trigger coil and outputs to the low voltage side of the ignition coil). Anyone know what this switchbox thing does? Have any ideas or suggestions? Thanx!

 

[Yepblaze]

Re: 1985 Mercury, 35 hp, Cold Start

Are you using the choke correctly. It needs to be held on for a few seconds after the motor initially starts then might need a couple of breif applications during that first start of the day. <br /><br />And then again if let to sit and cool down for a lenth of time.<br /><br />That could be the cold start issue.<br /><br />Then the warm running stalling and plug fouling could be carbs dumping fuel. Do they dribble gas when you prime em up using the primer bulb. That would indicate leakage past the needle/seat(s) and if that were the case the motor would have a tendency to sort of idle down and sputter out.

 

[jim dozier]

Re: 1985 Mercury, 35 hp, Cold Start

Check your manual to see if you have the right (recommended) heat range spark plug. If they are too cold a plug they will foul easily. If they are correct go on to plan B.

 

[Hooty]

Re: 1985 Mercury, 35 hp, Cold Start

Basically, what the "switch box" does is stores a charge (about 350v) generated by the altenator until it gets a signal from the timing coil. It then releases the charge to the ignition coil which steps the voltage up to 30,000 or so volts which fires the sparkplug and that lights off the fuel/air charge in the combustion chamber.<br /><br />c/6<br /><br />Hooty