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by Joe
(N. Arlington ,NJ)

Grimmer schmidt 125 cfm tow behind compressor Ford 302 gasoline Monoblock.

Grimmer Schmidt Mono Compressor
Grimmer Schmidt Mono Compressor

Engine runs great, just did complete tune up.

When I put a demand for air on the machine it begins to accelerate from idle but then falters and stalls. It acts as though the compressor isn’t warmed up.

It will run and make air with the service valve opened only part way.


by: Doug in s.d.ca.

Choke working OK? Timing?

Whatever, sounds like some engine problem, rather than the compressor.

What was the reason for the tune-up?


Grimmer Schmidt 125
by: Joe

Hi Doug.
Timing is set to 10 degrees BTC @ 100RPMs as per factory service manual.

The reason for the tune up was due to the machine stalling and running rough intermittently. Changed plugs, cap, rotor and wires. Motor still had issues. It would either run fine or start missing and stall. Found the problem to be a bad Ignition Control Unit. After I replaced that the motor runs great.

The choke is a manual cable operated, works fine. After my original post I tinkered more with the compressor and I was able to get full air from the machine but had to run it with the choke cable pulled out part way. But then the machine idles at 1500 RPM, too high.

So now I think it’s a fuel/carb issue. I thought it may have been an adjustment with the pace air control. The compressor valves and unloaders are all working correctly, unless I’m missing something.


Ford idle
by: Doug in s.d.ca.

Sounds like my truck…cold-blooded Chevy.

Can you readjust the idle with the choke on?

Maybe until you can get new/rebuilt carb?


125 mono block
by: Grimmerguru

You can’t open service valve all the way. When you do you lose all control pressure, due to the fact that a 3/4″ ball valve will pass more air than the machine can make.


Grimmer Schmidt 125
by: Joe

Cleaned and adjusted the carb. Added an in line fuel filter. There were no fuel filters on the machine. Re-checked timing and adjusted the idle.

Compressor runs like a champ now. Back in business!

THANK YOU to all who replied and helped with this issue, and to Bill for running this site and allowing me to post on it.


THANK YOU to all who replied..
by: Bill

Most welcome, for sure! 🙂

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