MF-135 Unusual Engine Noise Under Load

I have a MF-135 with the gas Perkins engine that makes a strange noise when I’m working the tractor. The tractor starts right up and runs fine it’s just that this is a new sound it’s making and I’m starting to get concerned. The sound seems to be coming from the left side (distributor and exhaust side) of the engine. It’s not a constant sound and it doesn’t sound like engine knock The sound has an “airy” quality to it and the best way I can describe it is the sound an air compressor makes when you turn the pump by hand, almost like a chugging/chuffing sound. The sound speeds up with increasing rpm when the tractor is moving or under load but the sound disappears completely when the tractor is just sitting. I’ve revved the engine to the same rpm while sitting and haven’t been able to duplicate the noise.

My first thought was that there was a hole in the exhaust manifold that gases were blowing through as the valves opened and closed but I’ve had no luck in finding anything wrong with the manifold. Does anyone have any thoughts on what I can check next? I did run the tractor for about a month without lead additive in the gasoline - could this have something to do with it?

I have a 165 gas that I run on unleaded gas with no problem. My suggestion is to check the valve adjustments. If that is good, do a compression test.

From what you are describing ,it sounds like an exhaust leak somewhere.I had that very thing happen to an older dodge truck when I first bought it.I would start it up and heard a very slight tick-tick-tick that got louder when accelerated.At that point I figured it was an exhaust leak and crawled under and,Lo and behold the manifold flange gasket was leaking.In order to quickly test for a leak,GENTLY place your hand over the exaust and you should hear the leak if there is one.Another one of my trucks has a couple pinholes in the main pipe,that also makes the same noise,so be sure to thoroughly check it out.Either way you can't go wrong adjusting the valves if it comes to that.

Rock