why do the lettered series john deeres have lazy cylinders

Just for my own personal knowledge because I like to know why, but can anyone explain why a lot of John Deere 2 cylinder letter series tractors have lazy cylinders. Some of them you here them always firing on both cylinders just pop pop pop popping along and other you here pop chug chug pop chug pop when idling, then you put them under load and the lazy cylinder goes away..

It's a matter of the carb placement. #1 is lined up with and gets most of the mixture from the carb, esp at idle when each cylinder is gasping for air/fuel. The #2 offset to the right is farther from the carb with sharper bends in the flow so it tends to get less later. This is aggravated by the fact that 2 fires right after 1 and then there's a lot of rotation before 1 comes up again to breath in and fire. At speed the flow is effectively continuous. The numbered ones have a duplex carb centered between the cylinders. Each cylinder has its "own" carb, through they share a common float bowl.

Interesting. Thanks for the explaination, but then why do some of them like the D on coke bottles fire on both cylinders at all times, bigger carb or are there other thingd involved

If I understand you correctly, I think you?re saying you hear some tractors with a non-regular, uneven idle ? something like ?pop, pop, ---, --- , pop,---, pop, ---, ---,---,pop,---, ---,---, pop, pop? etc. That?s really a result of a lack of tuning (bad carburetor, etc.) If they?re tuned properly and in good shape, they will idle very evenly and regularly throughout the RPM range, with or without a load. But as susandiane stated, the single-barrel carburetor on the letter-series tractors definitely starves the #2 cylinder at low loads/low throttle. You can really hear the difference at idle when you short out the #1 plug, then short out the #2 plug ? there?s not much difference when shorting out #2, but there?s a big difference in sound when you short out #1. But again, if the tractor?s in good shape and tuned properly, you will always hear a good, constant-rhythm ?pop, pop, pop, pop, pop?. And keep in mind that each ?pop? you hear is actually the combined ?pops? of both cylinders firing very closely together and since the opening of exhaust valves on both cylinders overlap each other a little, each ?pop? is actually a ?popop?. On the big ?D?s?, and especially ?G?s? at exceptionally low idle speeds, you can hear the individual ?pops? very close together, but at higher RPM?s it?s almost impossible to detect the individual cylinders.

As I understand, the letter series two cylinder tractors used a single barrel carburetor to feed two cylinders that were timed 180 degrees and 540 degrees apart. The number series used duplex (two barrel) carburetors that dedicated one barrel exclusively to each cylinder.

Sloppy governor linkage will result in erratic firing and unsteady rpm

Ben

because they are tuned up good. the D'S I had were the same it was pop pop pop pop no hesitation or pst pop pst pop. it was a nice rythem you could listen too. I even thought about using the idling john deere as drums in a band as that guy on u tube with that European tractor. was before his video came out. the D was my favorite john deere.

Like Rustred said below...a well tuned tractor with a properly built and adjusted carb will sit and bang as even and slow as you want. What you are witnessing is the fact that 50 % + or - a few, are NOT right and you wouldn't believe how many JD owners are falsely led to believe that they are running normal and have heard at the coffee shop "that's how they all run". LOL The two cyl JD's are their own worst enemy as they will "run" and operate and do their job , in very poor state of tune so that's how many remember them all their life. Yes' the letter series with single throat carb aren't quite as smooth at very slow idle as the two throat number series, BUY most will never hear the difference. Done right and tight...they all will idle down to about 250-300 rpm and even beat as you could ask for. I've tested hundreds of re-built carbs on my test tractor and they don't go out until they run like this. You are just seeing/hearing the "bad ones".

ONLY when they idle...the "Lead" cylinder sucks all the inlet fuel/air charge and the trailing cylinder gets very little...

Under LOAD, they even out..