180 cutting out

My 180 started cutting out( missing on 1 cylinder)
I noticed it the other day plowing it would change the exhaust note a bit, but did not feel loos of power.
Today it was getting worse, it is not all the time and will do it at all rpm's, idle up to 2000 rpm's.
I was planting sweet corn today when it did it a lot, still don't really feel a loos of power.
I tried to loosen injector lines to see if I could find what cylinder it is, and it seem like it is 4 the from the back of engine looking forward.
What happens it will start cutting out and the rpm's will jump 100. It can last 15 sec up to several minutes, then just go away again.
Any idea if it is a injector or the pump or something else?

Thanks

No smoke. When I loosen the injector line for that cylinder when it is acting up, it don't change the sound.
It do that on all the others,reason I believe it is the 4th cylinder. What I don't understand it why it go up 100 rpm when it happens

It sounds like a fuel problem to me.

Like Shameless said, I would check all the simple things first. Check the sediment bowl for a plugged screen and adequate fuel flow. (I once had a piece of dirt plug the top of the sediment bowl and restrict flow.) If that's ok, change your fuel filter. Check to make sure your hand pump is locked in the in the in position. Pump the hand pump and check fuel flow on the inlet line of the injection pump.

If it continues to get worse and gets to the point where it quits, or won't start at all, remove the fitting on the top of the pump that goes to the return line and try to start the engine. If it starts, and seems to run ok, you have debris in the check valve and you have internal injection pump damage (which is what I suspect). If that's the problem, you will need to have it repaired by a professional.

My 185 bears the scars of ignoring a problem like you describe with the first cylinder.  The previous owner ignored that issue for a bit too long and wound up with an overhaul.  The "scars" I refer to are the changed color of the paint on the block outside the first cylinder.  The previous owner kept good notes in the operators's manual and noted that he rebuilt the injector pump and replaced injectors about the same time as the overhaul.

I believe you should contact InjPumpEd.  

While you have the glass bowl removed, turn on the pet cock and make sure you have TWO STREAMS of fuel gushing from the base. If not, the sediment bowl inlet is partially plugged up above and needs cleaning.

It was probably starving for fuel and running too lean. I hope that took care of your problem permanently.