Chug, chug, chug like a John Deere
 

When under load, my car makes a distinct chug, chug, chug sound like a John Deere Model A. It's the sharp sound of compression or exhaust -- like a two-cylinder tractor. It's most noticeable from 25 - 40 mph when coming up to speed. I think the sound is becoming more distinct and more noticable -- enough to alarm me. Retarding the spark significantly or reducing throttle lessens the sound, but then there's little power for acceleration. Changing manifold gasket didn't help. Reducing spark gap may have helped slightly, but not much. I don't like the sound, so I reduce throttle or spark to avoid it, and it seems like I'm having to do that a lot more than I used to.

Compression at 7,600' elevation: 70, 48, 62, 40.
Compression with four shots of motor oil in each cylinder: 80, 60, 75, 50

Car has lots of power, clears every hill, 60 mph top speed at 7,000' elevation, never burns oil, light tan 3X plugs after 3,000 miles, no obvious manifold cracks.

But what is that chug sound?

Re: Chug, chug, chug like a John Deere
 

Seems like quite a variation in compression readings between cylinders ? Head Gasket . other things to think of re noise would Timing incorrect or alternatively manifold leak but you have looked at that -Karl

Re: Chug, chug, chug like a John Deere
 

In my opinion, your compression differences are way to big. I would start with figuring out why your compression is not right. I'm not saying this will be the fix to your noise, but it way help

Re: Chug, chug, chug like a John Deere
 

I had a very similar problem with my newly "restored" '29 roadster. Found the valves way out of ajustment.

Bob-A

Re: Chug, chug, chug like a John Deere
 

Where do you regularly position the spark lever for highway driving? Do you just advance to the bottom and leave it there? Do you have a high(er) compression head? When I lived in Parker it took me a while to learn proper spark adjustment on those Colorado hills (beautiful!) Not saying you are doing anything wrong, just wondering if you pull back on the spark advance when negotiating a long hill, that sort of thing. I beat the hell out of an A engine with too much advance and detonation that I was not smart enough to listen to. I sure know that sound now!

Re: Chug, chug, chug like a John Deere
 

Snyder 5.5 HC head.

I drive with spark advance at 1/2 quadrant most of the time, and rarely go full. The points open at 1-2 clicks down. Big hills require full retard.

Re: Chug, chug, chug like a John Deere
 

If you have slow closing valves Sea-Foam in the oil and in the gas should help. First I'd bring each piston to TDC on the firing sroke and apply air pressure, then see if it's coming out the car, oil filler, or tail pipe. If it hold air pressure OK, then it's probably slow to close valves and that should show up by using a vcuum guage on the intake.