The Ford Barn

macdonge · 11-11-2020, 05:13 PM

I'm trying, without much luck so far, to get a sensible tachometer reading on a '39 Merc 239 running on a test stand. It has a Bubba-built crab distributor with points and a Bosch blue (internal resistor) coil. The plug wires are solid core.

Am on my second tach - currently an Equus Performance and, prior to that, an el-cheapo (Trisco) - but neither one has been able to give me rational readings. I've tried the Equus in every possible configuration of inductive vs. hardwire hookup but still no joy. The reading keeps jumping all over the place. Sometimes it looks good but the next second can be two or three times what the expected rpm's should be.

Do you suppose the issue is that these new-tech tachs can't handle the 'noise' from the solid core plug wires (or the generator) ?

Thoughts?

11-11-2020, 05:13 PM	#1
macdonge Senior Member Join Date: May 2015 Location: Frelighsburg, QC Posts: 167	Crazy Tachometer Behaviour I'm trying, without much luck so far, to get a sensible tachometer reading on a '39 Merc 239 running on a test stand. It has a Bubba-built crab distributor with points and a Bosch blue (internal resistor) coil. The plug wires are solid core. Am on my second tach - currently an Equus Performance and, prior to that, an el-cheapo (Trisco) - but neither one has been able to give me rational readings. I've tried the Equus in every possible configuration of inductive vs. hardwire hookup but still no joy. The reading keeps jumping all over the place. Sometimes it looks good but the next second can be two or three times what the expected rpm's should be. Do you suppose the issue is that these new-tech tachs can't handle the 'noise' from the solid core plug wires (or the generator) ? Thoughts?