1973 18 hp Fouling plug

[w2much]

New points condensers all coils,rebuilt carb. Plugs keep fouling. If the plug comes out completely clean and white is this water intrusion?Will run and start then drop a cylinder , backfire, then not start.

 

[racerone]

Re: 1973 18 hp Fouling plug

Is there a thermostat installed ?-----------Compression test is required to see if gasket is blown.----Check to see if spark will indeed jump a gap of 5/16" or more.-------Clean plug may mean bad plug / no spark / no fuel to that cylinder.

 

[Bosunsmate]

Re: 1973 18 hp Fouling plug

if the plug rusts overnight its water.
If your piston looks cleanish its water too

 

[OptsyEagle]

Re: 1973 18 hp Fouling plug

The first question I have is: are you using the correct spark plugs. They should be Champion J4C. The second question is: how do you know they are fouling. If they are coming out shinny clean then I would suspect water contamination, but I would doubt that they would foul. Are the plugs coming out shinny clean? Do you see any water drops on them?

 

[w2much]

Re: 1973 18 hp Fouling plug

Sometimes they are just blackened with soot, sometimes half way to shiny clean. Yes J4j although J6j seems to run better. No, no rust.Yes there is a functioning thermostat.It seems that sometimes the top cylinder other times the bottom cylinder fouls out. Can not figure it out.

 

[mla2ofus]

Re: 1973 18 hp Fouling plug

Do a compression test.
Mike

 

[Tim Frank]

Re: 1973 18 hp Fouling plug

Sometimes they are just blackened with soot, sometimes half way to shiny clean. Yes J4j although J6j seems to run better. No, no rust.Yes there is a functioning thermostat.It seems that sometimes the top cylinder other times the bottom cylinder fouls out. Can not figure it out.

What are you using for fuel mix?

 

[w2much]

Re: 1973 18 hp Fouling plug

50 to 1 a bit richer than that actually, with sea foam mixed in. Just switched out the fuel pump also and the same symptoms.
How many turns out should the lean mixture knob be? I need at least three turns open(rich). Keeps running on 1 then 2 cylinders with backfire. Really has me stumped.

 

[geoffwga1]

Re: 1973 18 hp Fouling plug

I suspect your plugs.J4js have not been around for quite a while so they are pretty old.Superceded by J4c.Slow running jet out 1 1/2 turns from lightly seated for starters.Bit richer is good,I usually run mine @ 35-40 to 1,extra oil doesn't hurt.Make sure your points are good and clean and correctly gapped( 20 thou),clean with acetone or starter fluid.(don't use to start engine).I often come across this intermittent firing problem and it nearly always turns out to be some thing simple and silly.Good luck.Everything else as advised previously.

 

[w2much]

Re: 1973 18 hp Fouling plug

So this thing has had me baffled for a while . Let it sit and give myself time to think. The issue I found is that the top seal under the ignition plate is bad. It must be forcing an oily vapor out to be trapped under the flywheel and therefore coating the points with residue..I removed the flywheel and there was a puddle of oil near the driver coil. Cleaned everything up replaced the flywheel and started the motor.Ran great on two cylinders for about 15 minutes then started to backfire and then dropped the top cylinder , running only on the bottom cylinder. Anyway I ordered the seal and look forward to replacing it and getting this motor up and running. Hopefully removing and replacing the seal will go easy. Any suggestions on pulling the old one out without damaging the surface in which it is seated. I saw a special OMC tool for the procedure but do not have the luxury of having one.

 

[racerone]

Re: 1973 18 hp Fouling plug

Call your local dealer, they can pull the seal in minutes if flywheel is off.

 

[AlTn]

Re: 1973 18 hp Fouling plug

I've done as race suggests with both the f/w and armature plate removed and the local dealer pulled and installed the seal for $10/labor...the motor was on it's side in a minivan and the mechanic did it in place...as an alternative...google leslie tool 58430 as I believe this would work well also

 

[w2much]

Re: 1973 18 hp Fouling plug

Thanks for the replies. Looking forward to getting this one done.

 

[w2much]

Re: 1973 18 hp Fouling plug

So here we go again. Seal has been replaced(wood screw method, Hope I did not damage the O ring beneath). All new ignition parts, carb rebuild even a new pull cord(wore the old one out). Still not running correctly. Will start up and run fine for quite a while the drop the upper cylinder. I noticed that when the upper cylinder stops the bottom cylinder plug wire will show spark coming from the boot past the porcelain to ground out. New wires boots ect. When top cylinder drops there is still fire to the plug. When the engine is running on both cylinders I can touch the outside of the spark plug boot with a long screw driver and ground it out and of course it will drop that cylinder. These are new wires and boots this should not happen? should it?
Looking at the engine from the back (rear) which set of points are the top and which set is for the bottom.