g741.org

Last fall, my saga to completely rebuild my motor started with deciding to do a compression test on my newly purchased '37. Sort of just curious, as it seemed to run fine to me. So had my wife crank the motor, and found 1-4 were a bit low, high 80's, but 5 and 6 were 70 and 40. Nine months and hundreds of hours and thousands of dollars later, my truck starts instantly, idles fine, and has great power, and smooth acceleration and cruise. It should after being static and rotationally balanced.

But reading since that it you need to hold the throttle plate open to get an accurate compression reading, which I did not do, how do you do so with a carb that does not directly connect the throttle pedal to the throttle plate, but rather operates via the governor, not something I fully understand. So, how do you actually hold the throttle blade open on these vintage systems?

NV

Remove the side plate of the governor and hold it open there.

The governor defaults to WOT, not idle. The throttle return springs work to return the throttle to the closed position. If you want WOT press the pedal or pull the throttle cable handle. Loose the throttle connection and off it goes!

Having WOT during the test does not make much difference in the readings of the M37, but it will keep you from washing down the bores w/ gas. Cranking speed does have a significant effect.

Good information. I think I will close my gas line valve, and run the carb dry, then have less gas washing the cylinder walls, not a good thing.

always good to hear from those who "have been there."

NV

That really isn't necessary. With the throttle held wide open, cranking speed produces no vacuum and so does not put fuel through the carb. Choke closed is a different matter, don't do that

Forgot it defaults to open. Surely not enough velocity cranking to move it much.