Small Engine Fuel Pump Testing (pulse pump)

Disclaimer: This video is based on my experience and does NOT reflect the position of Kohler Company. This is NOT an official approved, recommended, or documented Kohler service procedure and is not present in any service literature.

You replaced the pulse pump multiple times and it still doesn't work...what next? This is advanced level pulse pump testing using a manometer.

Full Disclosure: In small engine repair, a manometer is intended for testing crankcase vacuum, not pulse pumps.
Crankcase vacuum can tell more about engine health in less time than it takes to find your leakdown gauge.
Learn more here:    • WHY Perform a Crankcase Vacuum Test  
And here:    • How to Perform a Crankcase Vacuum Test  

The digital manometer seen here can be purchased from Kohler: #25 455 22-S or DTI/Tiny Tach at https://tinytach.com/manometer
At the time of this writing (May 2023), they're about $100

For pulse pump testing, the manometer is best used for identifying if a pulse signal is present in the crankcase, and confirming this signal is nearly identical at the pulse hose. I think this is easier done with an analog manometer, but they've been discontinued and I can't locate a generic one online that indicates both vacuum and pressure.

As indicated in the video, there is no specification of "normal" crankcase pulses during cranking. Crankcase vacuum from a running engine will NOT be the same as what's observed during cranking either. The engine seen in this video makes about 10 inches of water vacuum running, yet the digital gauge peaks at nearly twice that during cranking. The analog gauge is again more useful here because it's not as fast to record peak values like the digital: it shows a peak closer to 15 during cranking.

I've only encountered one engine so worn that it no longer operated the pulse pump during cranking...and this was something ancient with a compression release mechanism to further reduce the compression of an already well-worn engine. The same thing could happen on a newer engine with a compression release mechanism (ACR)...it doesn't take much wear to drop compression to zero measurable when there's an ACR present.

Losing the pulse signal between the crankcase and the hose is quite common for any number of reasons as indicated in the video...and this is probably a more common reason for pulse pump misdiagnosis. Competing closely is poor flow from the fuel tank. A fuel tank should be able to siphon and gravity feed with strong flow as seen in the video. If it cannot, there's a problem between the tank and the pump.

Lastly, be careful to not confuse "fuel is present" during cranking with strong flow being present during cranking. This is (again) very subjective, and there's no way to precisely measure what normal fuel output is from the pump is during cranking, other than from mistakes and experience. I do know that increasing the lift height, increasing the pull length, increasing the resistance to flow (too small/restrictive filter); all reduces the volume of fuel that can be provided. Weaken the pulse signal or pump suction and this problem magnifies.