Proper sparkplug for 11.5HP B&S tractor engine

Hello folks,

I mowed with my MTD tractor the other day, and I realized that it became kind of... lazy in the last time. So I thought that I should replace the spark plug, never actually looked at it ever since I own it. And I realized that the spark plug isn't the one that should be in it. It's short, short for a OHV engine. AFAIK, OHV engines require slightly larger spark plugs (as my ripoff Honda OHV uses a extremly long one, also my Honda OHV bike does too).

After looking for info about the engine's OEM spark plug, I found it's correct name. There was a picture that measured around ~1.56cm thread lenght (from the start of the thread, to the end of it - not counting the electrodes).. is that correct? My car's spark plugs are the same lenght. I could order one from the internet, but the time it arrives, and do they even send it here, and if they do, + the delievery costs.. I could just buy a indentical one, with the needed lenght ofcourse.

The current spark plug is like the half shorter than 1.56cm thread length.

Anyways, do you guys think it's the correct lenght for it? I really wouldn't like the cylinder to hit the spark plug .
Also, with the current spark plug, the motor CAN NOT start without the choke on - but only when the MOTOR is cold, not the weather. When the motor gets warm, starts right up.

Engine model name (B&S, 11.5HP, OHV, I/C): 217807 0426
Spark plug model (according to the engine diagrams): 491055S
Tractor: MTD tractor, 2007-8 model, stock engine

Thanks in advance!

The standard plug for most briggs OHV engines is the Champion RC12YC or the NGK BKR5E

ILENGINE said:

The standard plug for most briggs OHV engines is the Champion RC12YC or the NGK BKR5E

Click to expand...

Thanks! Very helpful indeed. I'll look into the NGK one, the thread size is 14mm which sounds about perfect!
Thanks a lot!

Just one question.. did I lose a lot perfomance with the small spark plug?

It is possible that you were not getting full power. I would also be concerned about carbon build up in the threads if the threads on the removed plug were shorter than the required plug. May need to look into a spark plug thread chaser if the new plug doesn't screw in easily.

Just replace the Champion plug, and move on....

And the lazyness of the engine could very well be valves being out of adjustment.
Side valve engine tend go tight on the exhaust over time preventing full compression where as OHV engine tend to go loose.

Alright, thanks folks. I'll look into getting one and see if it gets it's full perfomance back.
Thanks!