Carburetor Adjustment and Timing Adjustment

I have a Farmall A that has been retrofitted with a distributor. It still has points. Anyway here are my issues:

The tractor was running a little rough, I have had issues with sticky valves and I got that freed up. The issue improved considerably, but the tractor still sounds like the RPM wavers a little and it just doesn't sound smooth like I think it should.

So...I attempted to adjust the carb. There is no power jet adjustment. Just Idle adjustment. No amount of idle screw adjustment makes any appreciable change in the way it idles. Screw it in all the way, runs OK, screw it out 5 turns...same. So, I rebuilt the carb. It was in pretty good shape anyway, but I cleaned it all out and got new seals in and a brand new idle needle. Still, the needle makes ZERO difference in the way it idles.

What is the deal with that??


Also, Timing adjustment. How do you do it? I have read a post here about turning the distributor 30 degrees CC and checking for spark, but no matter how many times I read the post, I cannot find a practical way of accomplishing this. I cannot locate any timing marks, so I am actually staring at Cyl 1 TDC through the spark plug hole. But how do you actually time it? Where is the procedure??

Any help on these issues is appreciated.

When the idle mixture screw has NO effect on how the engine runs, the carburetor is still dirty inside. Get a can of aerosol carb cleaner, and spray into every hole and orifice you can find. Don't stop until the spray comes out of a hole somewhere else.

If the idle is too high , the screw won't make much difference. Timing mark is on the
flywheel. Hard to find but it is there. When you think the piston is on TDC look on
the flywheel next to the bolt that holds the clutch pressure plate on.

I did exactly that. It's clean as a whistle.

Nevermind all of this. I cleaned the cap and rotor, and now the tractor won't fire or start at all.

Can someone please now help me diagnose what the issue is? I kind of feel like buying a new cap, rotor, coil, and wires and just knock all of that out of the question. I tried a new cap and rotor off another machine and got no response.

What do I do now?

Fold a dollar bill and drag it through the point gap. This cleans minor (non-conductive) garbage
out of the gap. Turn on the ignition (less than 3 minutes on) and use a plastic handled screw
driver to open the points. There should be a modest spark there. If you take the coil wire out of
the distributor cap, and place it 1/4 inch away from the block, and move the points as above it will
spark if things are OK. If nothing, you need a volt meter or a test light to go farther. The carb
idle ports are not clean yet. running a fine wire through them, followed by a squirt of carb
cleaner and air will get that done. Jim

OK. Your spark test succeeded. I have quite a healthy spark to the block as tested.

Uh...Now what?

OK. It started. No idea what the deal was. Maybe a wire wasn't seated?

It still sounds like it's missing. I don't know why or how, but the last person to time it did so by ear and I don't know how to make sure that was right. I did test my carburetor, I get some response if I force the idle really low and back it out about 4 turns. Otherwise, she runs fine with the seated. LOL.

How do I diagnose a miss on this thing?

If it missing you can pull each plug wire off one at a time (and then putting each back before moving to the next) to see if one cylinder doesn't cause a difference in how it is running. If you remove a plug wire and the sound of the engine doesn't change then you have found the cylinder with the miss. Try swapping plug, wire, etc, to a different cylinder to see if the miss stays with that cylinder.

Also, check for leaks in the intake manifold by passing an unlit propane torch around the flange. while the engine is idling. The idle will change if the propane is drawn in through a leak in the gasket.

Sounds like you may just have a "rolling idle", try slightly rotating the top of the distributor away from the block until the rpms just slight pull down and then ease it back just a little and see if it doesn't run smoother there.

OK. I'll test this out tomorrow.

As for the idle circuit on the carb, I took it apart again and got cleaner through every orifice in the idle circuit. It comes out somewhere else now. Still, you can literally seat the idle needle and it idles pretty good, in fact, I'd say it idles BEST with it seated. Not sure what that tells me.


How do you 'rotate the distributor'? The last one I worked on was 20 years ago on a 455 Olds. Here is a pic of the distributor with one of two nuts highlighted. Are these the ones I loosen in order to make adjustment to the distributor?

Here is my album. It's the only photo with a yellow circle.


https://photos.app.goo.gl/cTXoArQGjR9J4XXGA

Oh, one more thing, the 'miss' or hiccups seem to be somewhat random. It almost sounds like a lope, but not really. They also are sometimes accompanied by faint puffs of smoke.

Slightly loosen the two distributor hold-down bolts with a 1/2" wrench at the base of the distributor. They are located below where the coil wire connects, straight down, one in the front and one in the back.

Do you have your float height set correctly?

The random hiccup is probably not a miss and is probably just timing and fuel set incorrectly.

I just looked at your pictures and noticed that you have one of the hold-down bolts circled in yellow. There is another on the backside of the distributor.

Thanks! I m just really frustrated. The carb idle screw has me stumped. There is not other adjustment available on the carb in terms of power jets. It s fixed and has a plug on the outside. The idle mix screw, when seated, should stall the motor out and it doesn t. That bothers me and I don t know. What could cause it.

Tomorrow I ll play with timing and check for intake gasket leaks. Other than that, I know the circuit in the carb is clear so I m baffled and discouraged.

Sure appreciate the help, everyone.

Float is set "level" when viewed upside down. I don t have any leaks or flooding that I am aware of.

I time by ear most of the time, run engine full throttle, rotate distributor for maximum RPM. You will want to back it off a a little if it kicks back on starter or lopes at idle.

I bought a 1963 404 gas tractor that sat for some years. The gas tank was dry inside but smelled of rancid gas, no surprise there. I added fresh gas, removed the drain plug from the carb and let fresh fuel run out of the bowl. I started the tractor,drove it on the trailer and brought it home. The engine would run on all four but was not reliable or consistent in starting easily. There was valve lash noise but not terrible. The idle mixture screw was ineffective at adjusting the fuel mix lean or fat. I went through the carb first (marvel scheibler) and found the removable venturi was damaged and unable to seal against the upper and lower halves of the carb. I believe that allowed engine vacuum to draw air from the carb bowl / atmosphere. I rebuilt the carb with a new venturi and she starts and runs like it should and the idle mixture adjustment is effective.
Then I checked valve adjustment and found a bent pushrod on # 3 cylinder intake valve. The valve was opening but very little.
I don't know if the rod bent when I started the tractor or it was bent prior to my involvement, but I know that old rotten gas will cause valves to "stick" open or closed while engine is running or stopped.
Before I corrected those two problems the idle quality was poor and smelly with irregular "poots"out the exhaust. Now the poots are gone, the tractor starts easily without choke and idles low and smooth.
The small things are easily missed but have to be corrected.
Paul

Adjustment of the timing seems to have smoothed it out quite a bit to where I am satisfied. Carb still has an ineffective idle screw. I mean, It DOES kinda work, but it will run with it fully seated...not great, but it will run. From there you can back it out 2-5 turns and very little change is had. Doesn't really matter, It can and will idle so low that I don't know how it even stays running.

Anyway, the bad news is that I THINK I heard a knock now that everything is smooth and timed out right. Not going to worry about it, it has a long season of hard work ahead and when it gives up the ghost, we'll do a full rebuild on the whole shebang. I can't be sure about the knock as it is not all the time. I have only heard a rod knock on a car motor and it was nothing short of spectacularly obvious.

Is there a way to check for this and/or repair without removing the entire motor?

I must say I do not suspect 'rod knock'. Oil level is exactly where it should be and I tend to hear 'knocks' on a few of my machines....all of which have hundreds of hours since I decided they had a knock. LOL. It's probably just the way the motor sounds.

You may need to adjust the valves.
How does the oil pressure look?

I will just throw this out there, but you may have a leaking manifold gasket/hole in your manifold. Quick way to check is spray a little carb/brake cleaner on the intake portion of the manifold where the gasket seats. If the carb is clean and the idle screw isn't making a different an air leak would be where I'd look next.

Valves are adjusted to spec.

Oil pressure? Well, the gauge has it right in the middle.

I DO need to check for manifold leaks....that's the next step.

It seems to be running pretty well now. I do have a 'blip' occasionally as it is idling or running open, but otherwise, it seems to be firing on all cylinders and the timing is about right.