as long as the piston or valves don't come in contact with the spark plug it should be good but the rj19lm is very commonly used on Tecumseh engines. i don't think i have ever seen a different plug in one of these engines unless someone else put a different plug in.

 

The RN4C spark plug is for a (OHV) overhead valve motor and I'm guessing you have a flathead which does use a RJ19LM or J19LM plug. The RJ19LM plug, being shorter, will put the spark closer to the incoming fuel mix and probably make starting easier. I don't know the distance between the head and piston, but I'm surprised the spark plug didn't hit the piston. Page 62 lists the plugs used for different engines.


http://www.barrettsmallengine.com/manual/tecumsehreference.pdf

 

Do you have the Tecumseh OHV engine as that would take the longer plug, the short plug goes into the flathead engine.

 

Sorry for this question - how do I confirm if it is the OHV engine?

 

you will have a valve cover somewhere if you got OHV engine. if the area around the spark plug looks like this it is not a OHV engine

 

If you have a OHV engine you will see a small cover projecting from the engine on the side, probably 1 1/2" w x 3"-4" l x 1"-1 1/2" h. Out can also be a 4"x4" hex box sticking out.

 

Here is a pic of a 11.5hp with heater box taken off, you can see the L shaped tank and the small black valve cover right in the middle.

 

If purchased in 2007, I'd bet it's an OHV engine. Most significant difference is on most (if not all) the cylinder is angled while on something like the older Tecumseh flathead engines, the cylinder is vertical.
The picture is of a Tecumseh 10 HP I redid the other year, that's a flathead engine.

 

It is a OHV thus using the RN4C plug - thanks to all for your help - maybe the carb needs to be cleaned

 

hard staring is usually related to fuel/air mix, yes, cleaning the carb is the first thing to do especially if fuel was left in it for a prolonged period of time and make sure all passage ways and holes are cleared and also check everything between fuel cap and intake manifold

 

Can someone confirm the gap on the Champion RN4C plug ? Thanks

 

.030 "