Replacing the fuel lines or primer bulb on your string trimmer, chainsaw, or blower can look simple — until you see those two little nipples on the primer bulb and wonder: “Which line goes where?”

Image Credit Youtube Channel Chickanic

Don’t worry — you’re not alone. Whether you’re working with a Zama or Walbro carburetor, this guide will help you understand exactly how to connect your fuel lines to the primer bulb the correct way and what happens if they’re reversed.

What the Primer Bulb Actually Does

The primer bulb’s job is not to pump fuel directly into the engine.

Instead, it:

Pulls fresh fuel from the tank through the carburetor, and

Pushes the excess fuel and air back into the tank.

So when you press the bulb, it’s actually creating suction to draw fuel through the carburetor, filling it with fresh fuel for an easier start.

This setup ensures:

 Quicker cold starts

Consistent fuel delivery

Less wear on the recoil starter

Understanding Each Connection

1. Fuel Tank 

Inside your tank, there are usually two lines:

Fuel supply line: the one with the filter on the end.

Return line: an open line that sends excess fuel back to the tank.

2.Carburetor

Most small-engine carburetors (Zama, Walbro, etc.) have:

A fuel inlet port (connects to the filtered line from the tank).

A fuel outlet port (connects to the primer bulb’s suction port).

Here’s the important part — the direction of flow.

In short:

Tank (with filter) → Carburetor inlet → Carburetor outlet → Primer bulb suction → Primer bulb output → Tank return

What Happens If You Connect the Lines Backward

 Hooking up the fuel lines incorrectly is one of the most common mistakes people make — and it causes some frustrating symptoms:

Essentially, your engine will act fuel-starved — hard to start or won’t start at all.

Quick Test After Installation

After routing your lines:

Add a little fuel to the tank.

Press the primer bulb several times.

You should see:

Fuel moving from the tank → through the carburetor → into the bulb → back to the tank.

The bulb filling with fuel and springing back easily after each press.

If fuel doesn’t move or air bubbles stay trapped, check your routing again.

Hipa Pro Tip

When replacing both the fuel lines and primer bulb, take a photo before removing anything — it saves time and confusion later.

And for the best results, use a Hipa fuel line and primer bulb kit. Each kit includes high-quality, ethanol-resistant fuel lines, filters, and bulbs that fit most Zama C1U, C1Q, and Walbro WT carburetors — so you can restore your small engine’s fuel system quickly and confidently.

Final Thoughts

Connecting fuel lines to the primer bulb correctly makes all the difference between a frustrating no-start and a smooth first pull.

Remember:

Short nipple → to carburetor

Long nipple → to tank return

Get that right, and your small engine will prime and start like new.

Need replacement parts?

Explore Hipa’s fuel line and primer bulb kits

 — reliable, affordable parts trusted by DIY repairers and outdoor power enthusiasts.