9N tractor cannot get it to stay running, need ideas

I just purchased a house and it came with what I believe to be a Ford 9 N tractor. The tractor has been converted to 12v. When I go to start it fires and runs for about 5 seconds but never gets up to speed. I have checked the gas, installed new plugs, and just finished a carb rebuild. No change. I am new to this and I hope I am missing something simple. Any ideas on what I should do next?

Most common problem with these tractors is weak spark.
I would check that first myself, but to verify the fuel flow,
pull the plug out of the bottom of the carb, put a can under
it and turn the gas on. It should run a steady stream for a
minute or more. About a pint in a minute and a half.
Make sure you have at least 2 or 3 gallons of fuel in the tank,
and only open the shutoff about 2 full turns.
Opening it all the way gets you into the "reserve" which is
usually full of rust and sediment if the tank hasn't been cleaned.

If it doesn't, there are three screens in an N tractor to clean.
One in the elbow going into the carb, one above the glass sediment
bowl and one in the tank, accessed by unscrewing the whole sediment
bowl/fuel shutoff assembly. I leave it for last.
Check the gas you caught for dirt or water.

If fuel flows Ok, check for spark at the plugs.
Should be good blue/white spark, not weak orange/yellow spark.
Most common cause of weak spark is old/dirty/bad points.
They're not hard to replace/adjust. Search the 9N/2N/8N forum
on this site for instructions or help.
Don't be cheap. Buy quality points if you need them.

had the same priblem with a 8N...did the points, carb, plugs, timing...ended up to be weak springs on the distributor fly weights