1950 wd misses when warmed up.

Hey everybody, I need some help with a 1950 Wd. When it warms up it begins to misfire badly and if you shut it off it will not start until it cools of again. It has the six volt system with a distibutor. I have replaced the coil, plugs, wires, points, codensor, cap and rotor. Also ran a wire directly from battery to coil no change. This is a tractor I pickup about a year ago and has been rode hard, it came from a local apple orchard and put in many years of service. I am doing a preservation rather than a restoration to show the hard work she has done over the years. Any suggestion are greatly appreciated.

Believe I'd do a redo on the coil and condenser. Also check the compression hot and cold. See if the head gasket is blown between two cylinders or more. Start with the simple stuff first. Has it been converted to 12V? Check your volt-a-drop.

Thanks for the suggestion, still a 6 volt system. It may have had a mag originally, it still has the mag kill switch that is disconnected, a toggle switch was added. What will happen with the wd40?

What would be an acceptable range for compression?

Compression would depend on how worn the engine is. I would check for a difference in one or more cylinders. For example- 3 cylinders at 85 and 1 at 35 indicating a problem with that cylinder. What happens if you choke it or put a load on it when it misses?

The fact that it doesn't start when warm leads me to think it may be an ignition problem-maybe coil? Had one do that once. Could you put the old coil back on and try that? I assume you have checked the fuel system thoroughly-especially when it's warm and won't start?

I would take the good Doctor's advice!

Well you may have one or more issues. I am sure not a expert. But I do know that these will run when a lot of things are out of whack. (that's a technical term too):)
I think I would check for spark and gas both, when it wont start next time.
Regards,
 Chris

Thanks for all the great info and suggestions. It has good voltage and spark at the points when it won't start. The cap rotor and points all look like they are burning clean, no residue or odd looking burn marks. I am pretty sure it is not fuel related, when it starts to miss it seams like your turning the ignition switch on and off. It will almost completely die and then backfire. I could try the old coil again but the new one made no difference. I am going to get a compression gauge and check the cylinders, like I said this tractor is well used. I am going to try a new set of points and codensor. Any suggestions on reliable manufacturer? What exactly does the codensor do?

The condenser makes a resonant circuit with the coil primary so the current interrupted by the points oscillates and that is what makes a fat blue spark. In air that blue spark should be more than 3/8 long. In the process the condenser keeps the points from arcing and wearing asymmetrically as the condenser keeps to voltage down while the circuit is oscillating.

Some condensers are temperature sensitive and some can't handle the voltage and they get shorted by the high voltage. They tend to recover poorly but I have heard of them recovering when cooled for a while, like 15 or 20 minutes.

Gerald J.

I'll try and do a compression check tomorrow, if they are close when it is cold I'll check it again when it is warm and starts missing. It doesn't smoke or burn oil, the plugs are clean and look like they are burning clean. Thanks for the condenser explication, I never was sure how it worked

Just to throw it out there a few years ago I put new points and condenser in my B (wouldn't even start anymore with the old ones) and with the new tune up it ran great for the first probably 30 minutes of run time and progressively got worse and worse to where I could barely get it to fire anymore. Returned the points and condenser and got another new set and put it in and that was 3 years ago. It is a crap shoot sometimes with the quality of these replacement points and condensers and even coils depending on where you got it so just because you just replaced it don't totally rule it out in your mind if you don't find any other issues.