Using the primer bulb is key to successfully starting some mower engines. Sometimes just finding the primer bulb is the hardest part. You are in the right place, five minutes from now you’ll be mowing the yard.
A lawn mower primer bulb is located on the side of the carburetor, close to or on the air filter. The air filter is positioned on the opposite side to the engine muffler.
In this post you’ll learn how to find your lawnmower primer bulb, you’ll also learn how and when you should use it. Check out “How to start a lawn mower”.
Finding The Primer Bulb
Primer Bulb – Located on the air filter cover, close to the carburetor which is located opposite the muffler.
Primer Bulb – Located on the air filter housing.
Primer On Carburetor – Older mower primer bulbs are often located on the carburetor itself.
Primer Remotely Located – located close to the carb. Most modern mower primer bulbs are located on the air filter housing.
What Does Primer Bulb Look Like?
The primer bulb on a lawn mower is often brightly colored, red is common but black is pretty common too.
Primer bulbs are made from a durable rubber, however they are usually recessed into the air filter housing to protect them from damage.
The primer bulb is held in place using a plastic keeper ring.
Black Primer Bulb
Auto Or Manual Choke
Still can’t find the primer bulb? You might not have one. Not all mowers are fitted with a primer bulb. But all mowers will employ some type of system that adds extra gas on cold starts. If you can’t locate the primer, it is likely your mower doesn’t have one.
Instead, your mower may have auto or manual choke system fitted.
As auto choke is a selling feature, manufacturers usually proudly display a badge “Auto Choke”.
Otherwise look out for the choke symbol on your control lever panel.
How To Use The Primer Bulb?
Press and release the primer bulbs three times, that’s usually plenty of extra gas to start a cold mower engine. Primer bulbs are basic bits of kit, they commonly suffer from wear and tear. They become perished, mice find them irresistible. If a hole develops in the rubber bulb, it won’t syphon gas and distribute it to the engine.
Replacement bulbs are available are are easy to replace. Remove the keeper ring and remove the bulb. I cover the whole repair in this video here.
When To Use The Primer Bulb
Mower engines run at their best when the air to fuel is 14.7 to one – that’s 14.7 parts air to one part gas.
It’s referred to as the air fuel ratio or AFR. It’s important to add extra gas when the engine is cold, as cold air is denser and therefor is richer in oxygen.
The increased oxygen upsets the fuel ratio, and the fix is to add extra gas. Three basic types of fuel enrichment systems are common, the primer bulb, manual choke plate and auto choke. the primer bulb will be a prominent feature on the air filter housing. The primer bulb is only needed to start a cold engine. Warm engines don’t usually require extra gas to start.