420 won't start

JD Gimpl

Member
Hello Everyone,

I need some help. My trusty 1956 420S is hard starting and now won"t start. Cleaned carb twice with no luck. Front plug looks good, back it is all black including the white insulator. I only have 6 hours on these plugs.

It started about 3 months ago where it would run normal for 30-45 minutes and then seem to be robbing of fuel. I could pull the choke and it would recover most of the time. Now I can"t even get it to fire unless my son pulls me with the SUV and I bump start it.

Also when I crank and crank with the choke on then check the
Plugs they are dry. Can"t figure this one out and I have a bunch of mowing to do.

Any help much appreciated

Gimpl
 
You might consider changing the condenser.

We have a couple of 51 MTs that have the same problem on occasion.

Hope this helps.
 
either spark or gas. I would first pull the plug on the bottom of the crb and turn the gas on. If it does not have a steady stream coming out then you need to run that gas prob down.

if that is good jump a wire from the hot cable on the starter to the side of the coil that is not hooked to the dist. Crank and see what happens.

post back
 
I'd suggest adding a pertronix electronic ignition kit and having the carburetor professionally rebuilt (I'd sugggest popin John- Mike Shelby) as he knows more tricks about those Marvel-Schebler carburetors than anyone I know.

Best of Luck
Tyler in IL
Popin John Website Link
 
No spark while cranking due low system voltage. Too small battery, undercharged battery, too small cables and high resistance connections somewhere.
What is the coil"s primary winding ohms? What is the battery and coil polarity?
 
The battery is a 6 volt that is 2 years old. I had replaced the cables then as well. It is a positive ground system.

The coil is original from when I bought the tractor 12 years ago. How do I check ohm's?

Thank Gimpl
 
What is the CCA rating of the battery?
What size of cables?
Where is the chassis return/ground bolted to?
Coil's + should be connected to the distributed and through to the points.
Using an ohm meter. A six volt coil will measure approx 1.5 to 2.0 ohms across the primary terminals. A 12V coil will measure approx 3.0 to 4.0ohms.
 
that just circumvents all the wiring in the harness and provides the voltage direct. That is where you should have 6 volts when you turn the switch on.

I ran mine like that for a while until the new switch came in.
 
Hi buickandeere

I got the 420 started by towing it and bump starting it. It runs anywere from 2 minutes to 5 minutes fine and then starts missing or choking out like it is running out of gas. I pulled the plug on the bottom of the carb and fuel pours out of it fine. If I am quick with the choke I can keep it running most of the time.

This tractor has run flawlessly for the past 8 years so I am puzzled. Seems like it could be electrical or fuel.

I took the carb apart twice and it looked perfect inside so I am really wondering where to start.

Any advice would be appreciated.

Gimpl
 
Hi Dave,

I got it started by bump starting it behind the SUV today. Runs ok for a few minutes and trys to die like it is starved of fuel. I did pull the plug and fuel came out steady for a minute I ran it.

Would the switch cause problems intermitent?

Gimpl
 

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