Is this possible ( spark question )

[walkingfish]

Hi,<br /><br />1975 Merc 50Hp (500) 4 cylinder<br /><br />I have an oldie that i am in the process of getting going, I've still got to unblock the water channels, but i do get water from the prop when running.<br /><br />Is this (below) possible??<br /><br />After a 3 minute run, i pulled the new sparkplugs out and this is what i found.....<br /><br />1 - Slightly oily<br />2 - Clean<br />3 - Slightly oily<br />4 - Clean<br /><br />Could this be an indicator of weak spark?<br /><br />I used new plugs<br />All plugs produce spark when tested (grounded)<br />Compression is 95 in no.2 and 116 in all others<br />This motor has sat a long time<br />It only has one coil<br />The motor wouldnt idle but would run at about 2000 rpms<br /><br />Any help??<br /><br />Thankx,<br /><br />Brad

 

[Barnacle_Bill]

Re: Is this possible ( spark question )

If it has sat for a long time, most likely the carbs need to be taken apart and cleaned.

 

[walkingfish]

Re: Is this possible ( spark question )

Thanks IBNFSHN,<br /><br />I have noticed that when pumping the primer bulb that the floats dont seem to work.<br /><br />The bulb doesnt get "solid" but fuel streams from the carb throats, so a rebuild looks needed.<br /><br />But would that give me alternating clean / dirty plugs?

 

[WillyBWright]

Re: Is this possible ( spark question )

Nah. The upper two or lower two would look like that. The floats in those are wimpy. It's fairly easy to overcome them with the primer bulb. If they dribble when the motor is running, then you need new floats and/or float valves.<br /><br />The fuel pump is driven by pulses from two different cylinders. Again I think that would affect the upper two or lower two, but rebuild the fuel pump anyhow. The parts are cheap and that motor is probably overdue.<br /><br />I'm kinda thinking that you're losing spark to those two under compression. You might have spark leaking out of the wires with the sparkplugs installed. In open air, it's easier for a sparkplug to fire. Pressure and fuel add resistance. I imagine those plug wires are due for changing too. Run the motor in the dark and remove the cowl. You might see some fireworks in there.<br /><br />Then again, it could be reeds. Hope not.

 

[walkingfish]

Re: Is this possible ( spark question )

Thanx Willy,<br /><br />You are right that the fuel only leaks out when priming, when running you dont see any dribbles.<br /><br />Good thought on most problems affecting either the top 2 or bottom 2 cylinders.<br /><br />Unfortunately i cannot run the motor at the moment, the powerhead is unbolted and awaiting seperation to clear the water blockages.<br /><br />Is there a way to test the plug wires with an Ohm Meter?<br /><br />Could it be bad points causing a weak spark, seeing as how it appears on two cylinders that are "opposed"?<br /><br />Thanx,<br /><br />Brad

 

[walkingfish]

Re: Is this possible ( spark question )

^^

 

[Chris1956]

Re: Is this possible ( spark question )

Walkingfish, The spark plug wires are usually stranded stainless steel wire. Use a standard Ohn meter, and resistance should be virtually none. They wires fail when the spark leaks through the insulation to ground. Look for cracks and run your fingers over the wire while the motor is running to feel for the leaks. On this motor it is likely the bottom cylinder of a pair that share a carb will run rich. Are the clean plugs the result of extra fuel acting as a solvent?