Testors pipe bomb engine won't run

I've had engines that have sat around for a long time, building up residue on the glow plug coil for years. The castor seems to coat the wire, which is still going to light up just the same when power is connected, because the resistance of the wire remains the same regardless of how dirty it is. What happens when you disconnect the battery is that the wire is insulated by old hardened castor oil and is no longer in direct contact with the methanol in the fuel, which is what causes the catalytic reaction of the platinum. The engines need some good hard lean running to burn off the coating on the coil. I had a K&B Torp Jr with a type of glow plug insert which is virtually impossible to obtain. It glowed nicely when hooked up to a battery, but did exactly as your did. Disconnect it and it just shuts down, but with each subsequent run it would struggle on a little longer once disconnected each time. Eventually, after 3-4 tanks of fuel it would continue to run when disconnected. The other possibility is that the glow heads may have used a cheaper wire that was only platinum coated. It's possible that the coating has been eroded off over the years, leaving just the base wire which doesn't react to the methanol. The heads aren't impossible to find- new ones come up all the time on ebay, even if a little pricy, or old junk or unloved engines come up in parts lots which can be robbed of the occasional good head.

Rod.