Farmall M running rough

Hey all. I have a 45 M that I recently bought that idles rough. I've rebuilt the carb, put in new plugs, wires, cap, rotor, points, coil, condensor. It still runs rough at high and low idle, it might be a little worse than when I got it. Under load, it smoothes out, and has plenty of power. I've also adjusted valves, but they weren't off much. I am just out of ideas, and want to get the old girl running right.
 
I would look at replacing the 3 intake gaskets (2 manifold to head, and 1 carb to manifold).

Idle is very sensitive to the right air-fuel mix and the unmetered air from a potential leak can make it rough.

One way to help diagnose would be a very light choke to see if the additional fuel helps out, you could also carefully give some shots of propane near the manifold from an unlit propane torch and see if the vacuum draws in the additional fuel and smooths out the idle.
 
I've tried opening the choke some, and I've sprayed starting fluid around the manifold and carb. It makes no difference.
 
try closing the choke as that's what the other poster meant I'm sure. Opening the choke is the wrong way as it's most likely all the way open before you start moving it to see if idle improves.
 
dont know what u mean by rough, is it missing , surging, sputtering? have you checked compression? was the timing set then the carb set?remove the other three plug wires as you check each cyl. for firing. with tractor running at idle pull off the other 3 wires and leave only #1 wire hooked to plug.do that for all 4 cyl's. easy way to tell if each cyl. is performing. tractor will run on 1 cyl., if it stops on any cyl. thats your starting point.
 

The ignition timing is too far advanced. Loosen the bolts on the distributor and slowly retard the timing while the engine is idling. When it smooths out, stop right there and tighten the bolts. Engine should still have plenty of power and run smoothly at wide open throttle.
 
I also have a '45 M that did that. When I bought it, it would run rough and miss under no load, and smooth out and run great when under a load.

I switched from the Autolite spark plugs that were in it to Champion plugs and no more problem. I don't recall why, but I installed a new set of Autolite plugs and the problem came back. Put the Champions back in and it's run great ever since.

Why? I haven't a clue.

BTW, do y'all know that Champion and AC spark plugs are named after the same man? At the turn of the last century, when the automotive industry was in its infancy, a man by the name of Albert Champion began manufacturing spark plugs named after his initials, "AC". In 1908, he sold his business to Buick. He than started another plant manufacturing spark plugs and named them after his last name, "Champion". That's also why GM still uses AC spark plugs. I was afraid some of y'all had been laying awake nights wondering about that.
 
well what did you find? be nice to know on the outcome. everyboby seams to throw new parts at machines and wonder why they still have a problem. be nice to hear some feed back. i can take an old unit file the points clean the plugs, clean the carb, adjust everything to spec. and she runs pretty dam good. you dont rebuild the carb, you clean them, rebuilt carbs you buy.
 
what did the compression check read that should have been done before throwing money away for parts that were not needed all the new parts cannot make an engine run good if it doesent have good compression
 
Here's an update: I swapped out AL 386 plugs for AL 3116. It runs better at high idle now. you can hear it miss now and then. When the throttle is about 1/2 to 2/3 open, it sounds like it misses a lot. Someone suggested compression test. Will try that soon.
 
Also, I did try running one cylinder at a time. Each cylinder will run the engine alone, and they all sound consistent. I'm going to spread some manure with it tomorrow, and I'll let you guys know if it acts up more when it's warmed up.
 
I have a 49 M and it won't start without the choke fully engaged. And it won't run smooth without the choke engaged until it has warmed up fully. Once warm, it runs very well and has no trouble pulling a two bottom plow or running a post hole auger, which are the only real jobs it ever does.

On the other hand, I have a Super A, that only needs choke on the coldest days and warms up and smooths out very fast.

I think you have the right idea, put it to work and I bet it will smooth out and do fine.

Actually, both of my tractors sometimes have an intermittent little sputter that you might call a miss when cold and idling, but doesn't seem to affect the performance under load.
 
Another UPDATE: I spread manure with it for a couple hours today. When it warmed up, there was but a miss or two at high idle, but about half throttle on down, it sounds like it misses frequently. It sounds beautiful under load! It's a nice little tractor, and this is coming from a John Deere guy!
 
I finally got around to doing a compression test. I did it on a cold engine. All cylinders read 90PSI, and they all gained pressure similarly.
 
If that is an original distillate engine, then those compression numbers are great. If it is a gas engine, then they still aren't too bad for a cold engine. I bet all that's needed is a combination of timing and carb tuning to get rid of that last bit of flutter (the missing you referred to).

Do you have the throttle and choke wide open ? If not, it will lower the numbers a bit.
 
It's a distillate engine. Don't know what work it has ever had done. I goofed and did not open the throttle up, so I will do that and see if
it makes any difference. Thanks!
 
(quoted from post at 16:03:28 06/22/18) Another UPDATE: I spread manure with it for a couple hours today. When it warmed up, there was but a miss or two at high idle, but about half throttle on down, it sounds like it misses frequently. It sounds beautiful under load! It's a nice little tractor, and this is coming from a John Deere guy!

You still need to retard the timing a bit.
 
Tried retarding time. It helped some. Runs great cold. It starts to miss some when warm. I'm thinking it could be a valve issue?
 

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