1974 Harley Fouling Plugs

fwdstuck

A couple of weeks ago I bought a 74 Harley with steering wheel. It ran ok but had to choke it all the time (running lean). It had a mid 80s Columbia engine installed but with a Harley carburetor set up. Well done a check through the engine and the crank seal where shot, one of the crank bearings were wore and the piston was a little loose and run about 65 psi. So I done a complete rebuild of the engine, new crank seals and bearings, piston and rings with a good cylinder honing. Somebody has installed an plastic gas tank to replace the original metal front tank with a bottom gravity feed. Well after the first start up after the rebuild it ran great until it started dry fouling plugs. It will only about a day on a plug before it fouls. Carb is set a 3/4 turns open, points is set at .20, replaced the coil. What could it be doing?

BGW

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73eldo

What are you running for an oil mix? It ran great? New plug and it runs great for a while? How long does it run good?

fwdstuck

1.5 oz. supertech oil to a gallon. The plug I use is a new NGK BP4HS. Columbia engines use the shorter reach plug. I runs great, starts right up until it starts to foul the plug. It will run on a day or two before it fouls the plug. The will be covered in dry carbon.

Shepard

Your mixing 2 different technologies -- an old school engine with new tech oil. The plug your running is most likely what the book says to install in 1974 using 1974 2 cycle oils. IMO from what your explaining is the plug isn't getting hot enough to clean itself. I would go with a #2 plug instead of a #4. NGK plugs -- as the number goes down the hotter the plug.

fwdstuck

Well the body is a 1974, but the engine is a mid 80s Columbia (but pretty much same as a Harley engine) Harley engines use a longer reach plug, I think a BP4ES. Will a number 2 burn a hole in the piston?

Shepard

Your only going one heat range hotter in an effort to self clean the plug as it should.

backyard

I show 71-81 models use an NGK BP5ES gapped at 0.025". Are you sure it's not an 81 model or earlier?

fwdstuck

It has the later columbia (probably mid 80s) engine installed, it has the plastic shroud and flat top head. They take the shorter HS plug 1/2" reach instead of the ES plug 3/4" reach.

fwdstuck

Another thing is the carb floods too and drips fuel after the engine shuts off. I bought a new carb and it did the same thing so i put the original one back on. Runs fine when you put in a new spark plug but it doesn't take before it's covered with carbon and start making flooding symptoms and then won't start until a new spark plug is replaced.

backyard

Ok just making sure you had the right plug.

Having your low idle speed screw open too far will also foul out the plugs.

What carb are you using? Tillotson type or Walbro regular type?
If its the Walbro regular float bowl type, it sounds like the float needle is sticking open if gas runs out into the intake when the engine is off. It shouldn't be doing that and the float needle is the only thing that will cause that. That sounds odd because 2 carbs would be doing it.

I rebuilt a carb one time and put a little oil on the float needle rubber. Installed the carb and the oil cause the float needle not to seal for some reason. Flooded the intake instantly. I won't do that again. Are you positive your running 1.5oz oil to 1 gallon of gas?