3000 intermittent missing problem

I have a 3000 gas that has had a problem for three years now. At first it showed up plowing. It would run great with lots of power for a round or two then start to break up and miss badly. It would even backfire once in a while. Nothing I could do would change it. Then it would just clear up on it's own and run great again for a round or two. Pulling the chock would just make it start to flood, but wouldn't change the missing or power loss. I even stopped and work the throttle without any change. It just always needs a little time to clear up on its own. Then last weekend we went on a 20 mile tractor ride and it ran great again until I throttled down for a stop sign or after holding back going down a hill, it would start spitting and missing again for a short while then clear up and run great again. Once in a great while it would start missing just cruising along at 10 or 12mph without any warning. But more often after holding back or after slowing up for a stop sign. Things that have been changed over the last two or three years are the Fuel pump, all fuel filters including the tank. New better coil. New carburetor, Changed plugs points and condenser (twice). It seems electrical but just can't put my finger on it. The plug wires are about the only thing that hasn't been changed yet. I plan on changing them out next. But don't believe they could cause this condition. The charging system seems to be good. The battery is always charged and there is no warning light. There may be other electrical components that I'm missing. I've been battling this problem for three years now. The tough part is that I can't make it do it any time I want. It always seems to take quite a while of running for it to start doing it. Any suggestions or advice would be greatly appreciated.

Thanks
Joe

Definitely not a pro here but I had a similar problem with a different tractor and it was one of the plug wires was bad.

That's very interesting. I'm ordering new ones ASAP.

Being that the partial choke does not improve the condition, I am inclined to think it's an ignition problem.

Some things to check:

Worn distributor bushing causing the points to not remain set correctly. They can do some strange things, vary with RPM, temperature, etc.

Distributor cap and rotor. Have you checked the spark at the plugs? Could be loss through bad wires, rotor/cap connection, rotor or cap carbon tracked or rotor burned through.

Bad ignition switch or loose/corroded/mouse chewed/pinched/burned wire causing loss of power to the coil. Try temporarily connecting a volt meter from the + terminal on the coil to ground. Run it until the problem occurs and see if there is a voltage drop.

The quality of today's points and condensers is sometimes questionable. If there is some distributor shaft wear, or you suspect there may be a problem with the points, an electronic conversion can solve a lot of problems.

Other things to check not related to ignition problems:

Take a look at the valve train. Check the valve lash, look for a broken valve spring, sticking valve, dropped seat, bent push rod.

Is there any smoke when it misfires? Black smoke would indicate flooding carb, restricted air. White smoke, raw gas, eye burning smoke would indicate unburned fuel from lack of spark or loss of compression.

Exhaust backfire indicated erratic spark. Intake backfire usually indicates lean fuel/contaminated fuel, retarded ignition timing, valve problems.

All excellent suggestions. I have thought about converting to electronic ignition for some time now. Your so right about the quality of replacement points and especially condensers. They have been problematic for me in the past too. I'll start working my way down through your list until I hit on something.

Thank you so much for your expert insight and input.
Joe

ignition problems are usually steady.... except for heating up of ignition switches, coils or loose wires... so they seem to produce a continuous symptoms as a rule.....
So I would wiggle the ignition switch or throw cold water on the coil and see if problem goes away, if you can catch it when it happens.. I have seen wires that were broke inside the insulation and would cause the coil to cut off and kill the engine, especially where the wire fastens to the coil or ignition switch. I have installed a small bulb on the ignition side of the coil, to ground so I had a constant test light and could watch the voltage to the coil,, in some rare cases where it was a hard to find problem...

BUT.... its usually a fuel problem where something is moving around and clogging the fuel flow momentarily... something in the tank or in the carb or one of the screens

Or its getting the fuel lines hot and its vapor locking or boiling the gas in the fuel lines...


Occasionally if your running rich.. a piece of carbon can break loose and foul a plug , or cause a valve to stick and cause a cyl to misfire and back fire... check your plugs for carbon buildup.. and make sure your running an hd detergent oil to keep the valve stems clean...


the gas problem is usually first and foremost if it runs good the rest of the time.

Thank you for the input. I have checked the ignition switch during one of the bad times and it didn't seem to change things, so I think it should be ok. However I do wonder about vapor lock. With the fuel pump way in the front of the engine, there are allot of lines running along the side of the block. Even thinking of running an external line just to try for awhile. Never heard of the cold water on the coil test. But if I can get it to act up I'll give that a try too. If I can find it, I know I have a coil test light someplace to try that too. Lots a variables to consider. I hope it's not fuel. I've cleaned the tank, changed the fuel pump and lines. Changed all filters and installed a new carb last year. And after all that, nothing changed. Thank you so much for your suggestions. I appreciate all who have taken time out to help this old farm boy. Now I have lots of new things to check.

Joe