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If your Grimmer Schmidt air compressor is bogging down, and you can’t quite figure out why it can become very frustrating. Fortunately, this guide will provide you with the most common reasons why your Grimmer Schmidt air compressor bogs down, along with existing reader questions and responses.

Table of Contents

Most Common Reasons Why Grimmer Schmidt Air Compressor Bogs Down

Diagnosis of the problem may not always be so easy as there can be many things that can be the cause of the Grimmer Schmidt compressor bogging down. However, here is a summary table of some of the most common reasons why your Grimmer Schmidt air compressor bogs down and runs slow, with more details provided below:

ReasonSummary
Use of extension cordCan underpower the Grimmer Schmidt air compressor
Additional power-drawing appliancesCan underpower the Grimmer Schmidt air compressor
Faulty unloader valveWill need testing
Most Common Reasons Why Grimmer Schmidt Air Compressor Bogs Down Table

Use of Extension Cord

If an extension cord or power bar is being used, you should remove it, and plug the air compressor power cord directly into the wall socket to see if that helps. This is because the extension cord or power bar will underpower the compressor.

Additional Power-Drawing Appliances

If you have too many other power-drawing appliances on the same circuit as the feed to the compressor you could be heavily underpowering the compressor.

Ideally, an air compressor should be powered from a socket that leads directly back to a 15 amp (minimum) or a 20 amp breaker or fuse at the panel. If other appliances are in the line that feeds the compressor, you should shut them all down before you test the compressor again.

Faulty Unloader Valve

The compressor unloader valve is likely failing. To check this, you should open the tank drain and let all of the air out of the tank. This process will emulate the unloader valve function, and at the same time, remove any water buildup inside the tank.

After doing so, close the drain and power up the compressor to test it. If the compressor starts easily and runs up to cut-out pressure, it is now time to service or replace the unloader valve.

For more detailed information on this topic, visit our Air Compressor Bogs Down – Solutions & Diagnosing Problems guide!

Reader Questions & Responses

Grimmer Schmidt Air Compressor 125 Bogs Down and Stalls – Grimmer Schmidt Air Compressor Troubleshooting

Question

Grimmer Schmidt Air Compressor 125 cfm tow behind compressor Ford 302 gasoline Monoblock.

Grimmer Schmidt Mono Compressor
Grimmer Schmidt Mono Compressor

The engine runs great, just did a 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. Compressor bogs down!

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

Response

Choke working OK? Timing?

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

What was the reason for the tune-up?

Question

Hi Doug.

Timing is set to 10 degrees BTC @ 100RPMs as per the 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 and 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 partway. 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 of air control. The compressor valves and unloaders are all working correctly unless I’m missing something.

Response

Sounds like my truck…cold-blooded Chevy.

Can you readjust the idle with the choke on?

Maybe until you can get a new/rebuilt carb?

Response

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

Questioner

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.

The 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.

Response

Most welcome, for sure! 🙂


If you have any questions regarding a Sears air compressor bogging down, please leave a comment below, with a photo if applicable, so that someone can help you!