ORIGINAL: proptop
I had a feeling you just might be using a weak plug battery...
A typical glow plug will pull 2-3 amps...maybe a little more? (depends on the plug, and if it's flooded or not, etc.)
You really should get a good Nicad rechargable glow battery, because those dry batteries just don't have the amperage delivery capability, and will croak very quickly...(IMO they're not worth bothering with )
I have always used the alkaline batteries because I figured that 1.5 v was better than 1.2 v. I don't pretend to have tested this, but I guess that the internal resistance of the alkaline battery is enough to reduce the voltage on the glow plug side of the circuit so much that it's less effective. Makes sense to me, but I may try doing the measurements. I have a bunch of NiMH C-cells that I could charge up . . .
Thanks