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Figuring It Out What's Wrong

How to Troubleshoot Your Small Engine

With the simple design of small engines, repairing them is often very easy. However, figuring out what to repair usually takes the most time.

What's Wrong With My Engine?

Small engine mechanics generally rely on the maxim, "It's gotta be spark, gas, or air". To be more exact, there's a few other reasons that your engine won't run, but these are the first to check. Luckily, it's not difficult.

Fuel and Air Checks

First, check if you have gas. We've all made this mistake, and we've all kicked ourselves later.

Next, pull the air cleaner off. Inspect it to see if it's clogged with dirt, and if so, try starting the engine with it off.

If you're still hunting, grab a can of starting fluid and give the carb a squirt. This is a highly combustible material that gives the engine a short shot of fuel, even if the carb is plugged up and not delivering gas.

When the engine starts with the starting fluid, but dies quickly you'll know that you've got a fuel delivery problem, or a fuel/air mix problem.

Carb Problems

For delivery problems, pull the carb off and disassemble, looking for problems and clearing all passages. Most often the problem is just "gunk", but their could be a diaphragm problem, seal problem, etc. Check with a dealer or good book for your carb if you clean it and still have problems.

For the fuel/air mix, pull the needle valve screw out and inspect. Careful not to wrench these down, be gentle. B&S usually call for 1.5 turns out from the seated position.

Use good gaskets on the carb to tank and carb to block connections, otherwise a vacuum leak could be getting you.

Spark Check

If the engine doesn't start after checking the fuel/air mix, then head over to the ignition system.

Start by pulling the plug wire off the plug, and position the wire so that there is a small gap between the wire and the top of the plug. Give the engine a few pulls. A visible spark should jump between the wire and plug. You may have trouble seeing it in a very bright area, so if you don't see one, make sure that the gap is not too large and try in a shady area.

If you don't get a spark, then there's an ignition problem. Start by changing your small engine points.

If you do get spark, then your ignition is probably working OK. Remove the plug and inspect.

It will be helpful if you start to learn what a normal plug looks like, what a lean/rich plug looks like, etc. There's pictures in repair manuals.

If the plug is very dirty and sooty, you've probably got your carb's adjustments wrong. Clean the plug by spraying with carb cleaner and using a wire brush to remove the deposits.

Reinstall the plug and try again using starting fluid. If you're still not getting the engine started, then replace the plug.

Coil and Magneto Check

If you're getting a spark and replaced the points and still can't get it running, check the compression, and the coil and magneto, if equipped.

Use a feeler gauge to check if the coil to flywheel gap. For most Briggs it should be .006" (call your dealer/check the book for other models). If that's OK, ensure that the flywheel magnet is still magnetized. A screwdriver should be strongly attracted to it. Then move to check the coil. They rarely die, but can be tested at a lawn mower shop (or just swap another on it to check).


There's no listed compression check for Briggs engines, but the dealers say that when the plug is installed, the engine should pop forward when spun backward. We understand that many engines quickly leak down due to the valves, so a normal automotive compression check won't work. Call you local dealer to see what their ideas are.

If you've reached this point without getting it started, then you're in bad shape, and probably cussing up a storm. Pull the head and check the valves, they could be stuck.

That should get you going — Good luck!