Diagnosing a Small 4 Stroke Engine

This video shows the systematic method of diagnosing a small 4-stroke engine, like a lawn mower or go cart engine. Thanks to subscriber Rein Ciarfella for the easy to remember acronym FACTS that stands for Fuel Air Compression Timing and Spark. Use that as a checklist in any order to go about diagnosing and fixing the problem.

For this engine, I truly did not know what the problem was. But compression was the culprit, so I had to figure out why a new engine had none. The fix was simple after eliminating other possibilities.

Watch as I go through the steps and get this one back up and running!

[michiganmagneto]

I love working on small engines. So much fun and relaxing. Quite the opposite of driving a semi truck.

[mikea]

Very straightforward! Thanks for doing this! Save me alot of money doing my own repair.

[aaronmauro]

Thanks fella, had the same issue on a log splitter. Stored it with the engine sitting at an angle, cylinder head was dry. No compression. Little dab of oil and off she went.

[thercracer]

That one tip of dropping some oil into the cylinder really helped. I can get it started but it doesn’t idle

[samdean]

Thankyou for the great content. I've used all kinds of equipment but never learned how they work or how to fix them. Keep up the great work.

[brentmcknight]

Cheers for the video. I just bought a old quad bike that’s been sitting for a couple of years. It’s got spark and fuel and I was worried about compression. I will give your little trick a try. Fingers crossed

[xx]

Hi, i have a 24.5cc 4 stroke yarkking and how about 50psi and with oil put in about 60 psi. Too low? and its eating oil so i guessing last owner wore it out a bit. engine is 2 1/2 years old. Already stipped it and ring gaps are only .25mm at top where gap should be widest so not too bad. No leaks and some oil from breather with air exiting. but shes eating about a teaspoon every 10-20 mins!!

[MaxGunter]

Curious if the oil trick is more of a temporary fix? Once burned up wouldn’t the lack of compression persist? Then i believe youd have to replace the compression rings because sometimes those can wear or their the gaps become aligned or a groove or ridge was present in the cylinder wall? What are your thoughts?