Briggs Tank-Mounted Carb Repair

Article by Mark Trotta

All Briggs flathead engines with tank-mounted carburetors use a rubber diaphragm to pull gas up from the gas tank. A common problem is, the diaphragm dries out over time and needs to be replaced.

Briggs flathead carburetor repair

Another cause of non-starting is clogged internal passages. This is due to gasoline sitting in the carburetor for several months or longer.

Different Types Of Briggs Tank-Mounted Carbs

There are several styles of Briggs & Stratton tank-mounted carburetors. Some have fixed jets, others have replaceable jets. Vertical-shaft engines use a slightly different carb then horizontal crankshaft engines.

Pulsa-Jet vs Vacu-Jet

Pulsa-Jet carbs have two fuel tubes (a long and short) that stick out of the bottom of the carb. Vacu-Jet carbs have a single fuel tube.

If your Briggs tank-mounted carb has a primer bulb, it's a Pulsa-Prime carb.

Briggs flathead engine won't start

Some models have an automatic choke, which is internal and activated by a bimetallic spring. Many Pulsa-Jet carbs have a manual choke, operated by either a small lever (pictured) or a push/pull slide.

Carburetor Removal

The carb/tank assembly can be removed together as a unit. Older models built before 1993 had three mounting screws holding the carb to the tank.

Briggs PulsaJet carburetor repair

In 1993, a fourth screw was added for additional strength at the mounting surface. These were seen on 8 series, 9 series, and 13 series Briggs engines.

CAUTION: Make sure you have all the screws out before prying the carb from the gas tank!

NOTE: You can interchange a three-screw carb with a four-screw carb. Just remember to cap off the unused screw hole to keep out dirt and dust.

Diaphragm covers are often held down with slotted screws. The diaphragm cover on this Briggs 3.5hp motor was held on by four small Torx screws. To remove these, you'll need a T15 Torx screwdriver.

Briggs flathead tank mount carb

Replace Carburetor Diaphragm

Briggs 3.5 hp flathead engine

Although the old diaphragm may look OK, it may have gotten stiff with age or from lack of use. It's best to install a new diaphragm while you have the carb apart for cleaning.

Briggs flathead carburetor repair

This Briggs 270026 diaphragm fits just about all Briggs engines between 3 and 5 horsepower.


Carb Rebuild Kit

An aftermarket carb kit will cost much less than an original equipment kit. Have the engine model and serial number handy while ordering.

Briggs tank mount carb rebuild

Shop: Briggs Carburetor Rebuild Kit

The carburetor overhaul kit will fit most Briggs & Stratton 3hp to 5hp engines. There's about 20 parts in it, and you'll probably have most of them left over when you're done.


Replace Rubber Grommets

These rubber grommets are a common source of vacuum leaks. Replace them if they're old.

Briggs grommets 692187 692189

Shop: Briggs&Stratton Breather Tube Grommet Kit


Carburetor Cleaning

The majority of carburetor rebuilding is cleaning. Gumout carb cleaning spray is a good product to use for both inside and outside the carb.

Internal Cleaning

Carb cleaning should include the internal passages. If they are not clear and clean, the engine will not run right. To clean out the small passages, you can use carburetor cleaning brushes, or a welding torch tip cleaner, but an old guitar string will work just as well.

NOTE: Take care when cleaning the passages, as the carb body is made of soft aluminum alloy.

Soak the Carburetor

If the carburetor is really old and dirty, invest in a gallon can of Berryman's Chem-Dip. A dunk basket is included.

rebuild Pulsajet carb 3.5 Briggs

This stuff will dissolve sludge and dried-up remnants of fuel, but it will also eat rubber and plastics. When done cleaning, you can rinse the carburetor with water, then dry with compressed air.

After soaking, use a soft nylon brush (or an old toothbrush) to clean the outside of the carb. When done, blow through all passages with compressed air.

After soaking, you'll need to run something through the small passages again to remove any stubborn debris that has softened and loosened.

carburetor cleaning brushes

Shop: Carburetor Cleaner Brushes


Remove/Replace Pickup Tube

The fuel pickup tube(s) that extend down into the gas tank can usually be cleaned and reused. Regardless, they should be removed so you can clean the internal parts of the carb.

Briggs Pulsajet carb rebuild

Some tubes have a hex-shaped "foot", and you can use a socket to remove it. If not, grab the plastic part of the tube with pliers and twist it off.

Caution: The brass portion of the pickup tube stays in the carb. It is press-fit into the carb casting.

Briggs flathead carburetor rebuild

Install the tube with the retainer ring on it, then push it down onto the brass tube. It can be stubborn going back on, so here's a few different ways to do it:

Put a few drops of oil on the brass tube before sliding on the plastic tube.

Heat the tube in hot water before pressing it onto the brass tube.

Heat the tube with a hair dryer before pressing on.


Replacement Carburetor

If you can't or don't want to repair your old carburetor, replacements are inexpensive.

Briggs flathead engine repair

Shop: Replacement Carburetor For Briggs 5hp Engine


Misc Notes

If you break the tank to carb gasket, make sure to replace it, as it needs to seal tightly for the carb to work correctly.

Do not use RTV gasket sealer on any of the carb gaskets, it's unnecessary and can clog up necessary passages for the engine to run. Lightly coating gaskets with oil will help them stay in place during reassembly.

The pre-set for the needle valve is 1-1/2 turns out from lightly seated.


Briggs Air Filter

Briggs flathead air filter 491588

If you're replacing the 5-1/4" x 4-1/2" panel air filter, it's part # 491588 or 491588s. You can buy one here.


Related Articles:

Vintage Briggs &Stratton Engine Identification
Briggs 3.5 HP Flathead Engine
vintage Briggs engine

Read: Briggs 5HP Flathead Engine