1973 18 HP Fouling Plug

[w2much]

Can not keep this thing running on two cylinders. Plugs are new. Sometimes the top cylinder plug then sometimes the bottom cylinder plug will stop firing. Always good spark from the coil to the plug but the plug fouls out. I think it is water intrusion. Compression is even at 90lbs per cylinder. Might a bad exhaust cover gasket cause this issue? Or might the head gasket? Runs good for a while then one cylinder starts to miss then dies and will continue to run on one cylinder. Plugs will come out one a bit whiter than the other, the whiter one being the fouled plug.

 

[Bosunsmate]

Re: 1973 18 HP Fouling Plug

with water its normally grey milky residue.
any rust on plugs?
are piston heads looking steam cleaned ?

 

[boobie]

Re: 1973 18 HP Fouling Plug

The spark should jump a 3/8" open air gap on a tester. Checking it with a spark plug is useless.

 

[racerone]

Re: 1973 18 HP Fouling Plug

A cold running cylinder will not keep the plug clean.-----------Is the thermostat installed ?---------Do a proper spark test as a system with good spark can easily jump a gap of 3/8" or more.-----Sparkplugs are very well made and usually they are not the problem.

 

[w2much]

Re: 1973 18 HP Fouling Plug

No milky residue, no rust on plug, piston heads not steam cleaned.Weak spark appears to be the issue. Bottom cylinder jumps 3/8" barely, .top cylinder has weaker spark. Changed out the driver coil, cleaned and regapped the points and changed the condenser . Started right up ran on two cylinders then the top cylinder started to miss. How do I get a hotter spark?Bigger gap, smaller gap. Certainly at wits end but still determined to get it right. Your answers and suggestions are appreicated

 

[Bosunsmate]

Re: 1973 18 HP Fouling Plug

Is it backfiring or just missing?

 

[w2much]

Re: 1973 18 HP Fouling Plug

A bit of both. Mostly the weak spark will kill the cylinder. What do you think?.

 

[Bosunsmate]

Re: 1973 18 HP Fouling Plug

thoughts are if you are still getting weak spark then what else is there in the system that is causing that? Only wiring corroded?

if i thought it was water getting in there, which i cant see you have enough evidence for at present i would then drop out the lower unit and run it for a little bit and see if no water helped.

backfiring normally means fuel shortage in my experience. a miss- electric