Ford NAA that just won't start. Ran great last year, put the battery back in this spring and for a while it would only fire if the starter cranked. Now it doesn't fire at all. What I've done: new plugs correctly gapped, new carburetor, new sediment bowl, checked the intake manifold for obstructions, reground valves and reset valve clearances, check for strong spark in all four cylinders (it has an electronic ignition), checked timing best I can (no marks on flywheel - only dabs of paint), checked compression (60-80 which is what it was when it ran great), replaced the coil and relay. Any theories or ideas for what I might try next?

When ever I get stumped like that, it turns out to be water in the gas, bad coil connections, or grounded points.

6V/POS GRN or 12V/NEG GRN? FACT: 99.98% of all non-starting/non-running issues are due to incorrect wiring. EI accounts for many FUBAR setups. A weak or dead battery is the usual culprit when starter motor just cranks without turning over. Take battery to a shop and have it tested on their machine under load. You won't do nothing just be connecting a basic garage trickle charger. Next, why did you just start replacing parts willy-nilly? Guessing is never an option. True Root Cause Problem Solving Methods must be used for every problem. Part needs to be proven defective before you replace it. Timing hash marks on flywheel should be ether - look closer. Distributor tuned right? Starter Motor is a 3-WIRE UNIT that use a RELAY (SOLENOID). 6V use the 20A 2-Brush GEN and the FAG-10505-A Voltage Regulator. A 12V conversion eliminates them both and instead inserts a 12V ALTERNATOR, DELCO 10-SI 1-WIRE typical. Either one used you must have a belt tensioning bracket installed. Compression is a little low but that is not your problem. Get manuals and all wiring verified first. Report back.

Tim Daley (MI)

Water in fuel?

Gas dripping from carb while over choking?

Hold your hand over the carb inlet while cranking. ....Do you feel a strong suction?

It is possible to have a good compression reading, without pulling a vacuum at the carb inlet.

On two different tractors (NAA & 640), the manifold rusted/corroded through between the intake and exhaust portions. ...Good compression, but no vacuum at the carb.

A shot of starting fluid to see if it barks.

Tried that, too. In addition, replaced the fuel line and wiring.

If it didn't bark on ether, then either the plugs are fouled or you have no electricity.
Time to get out either the volt meter or that trouble light and go looking for a loss of juice. Key on voltage at coil? Going to the key? Out of the key?
If you have spark at all 4 and ether didn't make it bark, then your missing compression or timing.
At this point you should pull the plugs and either clean them up/dry them out or install new.

How far does the spark jump from the wire to the plug> If 1/16 to 1/4 in., bad ignition. The old points system would mean a bad condenser. I don't know anything about the electronic.