Brush Hogging with 57 420

[slongway]

About a year ago, I rescued a 57 420w from the weeds. Ive spent a fair amount of time getting in relatively mechanically sound...after I had to free up the bottom end. Rebuilt carb, new top end gaskets, radiator repair, all new wiring, functional gauges, etc. Im not at the point of making it pretty, still in the working out the bugs stage.

It starts and runs pretty amazing for its age... about one revolution and shes going. After a number of trips driving around pointlessly to give it some use, I decided it was time to load it up and see what it could do.

I hooked up to my brothers 6 brush hog, and while I know its too much mower for this machine, Im not new to tractors, I figure I can go easy and make it work. And it did, for a little while.

Short version, with no tach, Im spinning the PTO up by ear, which was essentially wide open. And it did great, until I fouled a plug. Ive since been through a number of things trying to keep it running long enough to knock down the rest of my field.

Based on some research, I realized it was really struggling to keep temperature, the cooling system was doing too good a job, and my stat probably wasnt closing. Put in a 180 stat, and now she holds temp nicely. I replaced plugs, after verifying my all new 12V ignition system was blasting really good spark, and I added a second washer on the plug, as recommended by some old timers.

For background, Ive compression tested, and am running 120/120. Todays run was the first time Ive used any oil, and based on the 90+ it was out, an the 180stat, and as long as I ran it, I dont feel bad about cooking a little oil on this old girl.

So anyways, I ran it today, and tried something different... I ran it at about 3/4 throttle, which by ear sounded a little slow for the hog, but other then having to ride the first stage of the clutch pretty frequently to keep it from getting into the governor too long and fouling a plug, it got the job most of the way done. I did eventually foul a plug trying to escape a ground wasp nest I got into.

The question finally... is my experience normal for a 420? I expect a 4 hog would probably not be require me to avoid letting the governor do its job, but Im questioning if thats just expected with this old girl. She sounds so good when loaded down and making some horsepower, I just never guessed that it would foul plugs in that scenario. And to be clear, its always the radiator side plug Im fouling. Im running about 1 turn out on the load adjuster.

Would love some criticism / insight here. Thanks in advance.

 

[Russ from MN]

A 6 foot cutter is a lot for a 420, but it depends what you are mowing. I had a 5 foot on our M, it would mow grass/weeds OK, never took it into any brush. It was too heavy for the M, I used it without the top link connected. My neighbor uses a 5 foot on their 420, but only in grass/weeds. If you were close by I could check the PTO speed with this revolution counter to see if the governor is set correctly, it should run a little over 540 at full throttle.

 

[slongway]

It’s about 2 years of growth on an old hay field... mostly just really tall grass, some small woody stalks, not actual brush, by my definition, but others may disagree. Thanks for the confirmation on the PTO speed, about full throttle sounds right, based on experience mowing with other tractors.

 

[buickanddeere]

Working the engine hard at full operating temperature should make it less likely to foul a plug vs putting around at part load and throttle .
What spark plugs ?
How did you set the carb ?

 

[Brendon-KS]

I have a 4-ft cutter that I use on my M and I've used it to mow down some pretty tall, rank growth. In really nasty conditions it makes the tractor work hard but I've never been in
anything that I couldn't make a full width cut in. Your 420 is rated for half again as much power as the M (28 hp vs 19) so in theory it should be able to handle half again as much mower.
Even if not, having too much load for the tractor will only cause it to bog down - it shouldn't cause any plug fouling or other damage. Any time you're running at full rated power the
governor will have the throttle wide open and the tractor is designed to operate at this level continuously. To be fouling a plug so readily would point to some problem with your tractor,
not to a usage condition. Worn valve guides, maybe?

 

[slongway]

(quoted from post at 04:30:25 08/24/20)
Working the engine hard at full operating temperature should make it less likely to foul a plug vs putting around at part load and throttle .
What spark plugs ?
How did you set the carb ?

I've been trying different plugs, and unfortunately nothing has been very scientific with this process. Started with Autolite 216, and those fouled (after I learned I wasn't charging and the spark was likely getting weak). Resolved charging issue, and start over. I switched them out to Champion H10C, as I had a couple of them handy, even though I'm not a fan of champs. That was before I put in a 180 thermostat. Yesterday's run was with an NGK cross (what I was able to grab at a parts store), N4L I believe.

Carb setting wasn't real scientific either, I think I'm about 1-1/4 to 1-1/2 out on the idle screw, and adjusted the idle speed to make it lope along nicely. I'm about 1 out on the main load adjuster. I have never messed with the governor, and I see no signs that it has ever been messed with in the past.

I have noticed that the load adjuster has about just about zero impact on how it runs, which would normally tell me my main jet passage was partially plugged, but the plugs don't tell that story, they certainly don't look to be burning lean. It also really doesn't smoke, or use any oil to speak of. I don't know, maybe I'm misreading oil soaked plugs for gas soaked, and I'm starving it for gas?

 

[slongway]

Starting to think the same thing (valves leaking oil into the chamber)... I probably should have had the head re-done when it was off, but that was early in the revival process, and I didn't want to sink a bunch of money in it until I knew it was going to run.

 

[buickanddeere]

Autolite 437 have the longer reach required to put the spark plug tip into the combustion chamber .
The 437 is also non resistor .
Is the entire air intake system from snorkel to carb clear of mud, manure and bugs ?
Idle should be set as lean as possible without bogging , stalling or idling rough .
Main should be set as lean as possible without loosing power .

 

[M-MAN]

Dubuques don't foul plugs when working unless something is way off. Your compression numbers say your valves are good but if the lash is set too tight when it gets hot
from working they won't seat properly. An overfilled oil bath will allow oil to be pulled into the engine while working. With a good properly timed ignition system you ca
move back to the carb. If adjusting the load needle doesn't get a good response in both directions you definitely have blockages left in the carburetor that need to be
addressed. There are three tiny holes in the throat that must be cleaned out along with the ones in the nozzle itself. Load nozzle and idle jet and economizer jet has to
come out to clean. Carb linkage is set 1 & 1/2 rounds short while the governor linkage is set 1 & 1/2 rounds long.

 

[slongway]

Air intake system is clean. I did learn after the first go-round with fouling that the oil bath was slightly overfilled, so I dropped that back down to the line to limit the possibility that oil was wicking up through the breather mesh.

 

[slongway]

Sounds like I gotta drop the carb back off it and clean the main nozzle area again. Guessing the port where the load adjuster drops into the nozzle is the culprit, if everyone normally expects that to have some real impact on the tuning (it has almost zero impact now).

Curious - has anyone ever tried dropping just the bottom half of the carb off? Thats where all the action has to take place. Maybe I'm thinking too lazy here.

 

[buickanddeere]

The intake manifold has no hidden cracks or holes ?

 

[slongway]

I had the intake manifold off when I pulled the head, and it looked good. I suppose I could spray the manifold with some ether while its cold and idling and see if it affects the idle, but I'm don't believe I'll find anything. Worth a look again thought, thank you.

 

[slongway]

Just to close the loop here, I did finally get to the bottom of this... I had a fuel delivery issue. When I took the sediment bowl off to clean the screen, I checked to make sure I had good fuel flow from the tank, and it was a dribble with the valve fully open. Cleaned that out, and no more issues. Obviously I was misreading oily plugs for gas soaked plugs.

In the process leading up to this, I also pulled the carb back off, removed and cleaned out the main jet area (which wasn't blocked, but it wasn't great either, it was a good move to clean it), and realized I had my main load jet improperly installed, meaning what I was reading as bottoming out was me bumping against the packing. Just another humbling example of me learning that 63 year old mechanicals have some nuance to them.

The 6' brush hog is still ALOT for this old girl, but it did the job well, especially considering how tall the brush was getting to be.

Thanks everyone for the help, greatly appreciated.