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.
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.
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.
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.
Replace Carburetor Diaphragm
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.
This Briggs 270026 diaphragm fits just about all Briggs engines between 3 and 5 horsepower.
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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.
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.
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Replace Rubber Grommets
These rubber grommets are a common source of vacuum leaks. Replace them if they're old.
Shop: Briggs&Stratton Breather Tube Grommet Kit
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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.
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.
Shop: Carburetor Cleaner Brushes
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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.
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.
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.
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Replacement Carburetor
If you can't or don't want to repair your old carburetor, replacements are inexpensive.
Shop: Replacement Carburetor For Briggs 5hp Engine
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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.
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Briggs Air Filter
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.
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Related Articles:
Vintage Briggs &Stratton Engine Identification
Briggs 3.5 HP Flathead Engine
