This problem is usually common with Briggs and Stratton Vacu-Jet and Pulsa-Jet diaphragm style carburetors.
A.The diaphragm is stiff and must be replaced. This top information is for carburetors installed on Sprint, Classic and Quattro 3.0 to 4.0 hp engines.
1. Remove the two bolts holding the gas tank to the engine.
2. Tilt the carburetor and gas tank as a whole towards the engine to free the governor linkage from the throttle shaft.
3. Dump the gas from the tank into a container suitable to contain gasoline. Set the tank on a work bench.
4. Remove the 5 machine screws holding the carburetor to the tank. NOTE: **ON SOME MODEL SERIES 110900, 1119000, 113900 AND 114900 THERE WILL BE ANOTHER LONGER SCREW INSIDE OF THE AIR HORN UNDER THE CHOKE PLATE. BE SURE TO REMOVE IT SO YOU DO NOT DAMAGE THE CARBURETOR.**
5. Pull up on the carburetor to remove it from the tank. Make sure the springs do not jump onto the floor. If you notice a pool of gasoline in the large, shallow well in the gas tank top, then the tank must be "trued". Gas in this area affects the pumping action of the fuel pump. If a local Briggs and Stratton authorized shop cannot true the tank, then the tank must be replaced.
6. On automatic choke engines, you will have to remove the access cover on the air horn (located on opposite side of the breather grommet) to remove the link connected to the diaphragm to remove the diaphragm.
7. Check for debris clogging in intake straw. Clean the screen with a tooth brush if necessary.
8. Install the spring to the bottom side of the choke link. No more than two coils should be in the holder. Make sure you do not damage the spring when installing.
9. Hold the carburetor upside down in your hand and place the wide, short spring in the correct well (caburetors needing the 391681 diaphragm use this short, wide spring). Then place its cup overtop the spring. Pulsa-Prime carburetors will use a gasket and diaphragm and a spring. The diaphragm will go ontop of the tank, then the gasket. The spring fits on a boss on the bottom of the carburetor.
10. While holding the carburetor upside down, place the tank over the carburetor. Put the carburetor and tank assembly right side up on your bench and start the 5 screws. Do not tighten them yet. Connect the choke link to the choke shaft. Close the cover.
11. Put a screw driver or something in the air horn to hold the choke plate open, past halfway. Jiggle the carburetor to set the choke spring. With the screw driver still holding the choke open, tighten down the screws in a staggered seqence. Then install the longer screw inside the air horn, if equiped.
12. Reinstall the carburetor to the engine in reverse order as stated above.
IF YOU HAVE A 3.0, 3.5 OR 5.0 HP HORIZONTAL SHAFT ENGINE, THEN...
1. Remove the muffler and the breather tube. If it is easier to remove the whole fuel tank and carburetor assembly, then remove the bolt at the bottom of the support bracket and the two bolts holding the carburetor to the block.
2. Remove the four screws holding the diaphragm cover on.
3. Take the diaphragm and a Model, Type and Code number to a local Briggs and Stratton dealer and have them identify the diaphragm as New Style (P/N 272538) or Old Style (P/N 270026).
4. Hook the hole of the diaphragm to the pin located on the carburetor near the block. Then insert the spring first into its dish and then put the cap on top of the spring. Hold the diaphragm in place while installing the diaphragm cover.
5. Tighten the screws tight and reinstall the breather tube from the breather on the block to the carburetor. Reinstall the muffler or the whole fuel tank assembly.
B. High speed nozzle or jet is partialy clogged.
On all Tecumseh float style carburetors, remove the bowl nut and clean out the holes in it. On adjustable high speed engines, make sure you find the tiny hole on the top of the first set of threads. It can only be cleaned with a piece of tag wire.
On Briggs and Stratton, All Max and Quantum engines (3.5,4.0-6.5 hp) will have holes in the bowl nut. Clean these out. On all other Briggs engines, there will be a removable nozzle. Take this out. NOTE: **DO NOT DAMAGE THE THREADS WHEN REMOVING OR INSTALLING THE NOZZLE. PURCHASE BRIGGS PART NUMBER 19062 TO GET A SPECIAL SCREW DRIVER TO REMOVE THE NOZZLE.** Remove the nozzle and clean out all the holes. Reinstall. Opposed Twin Cylinder Briggs engines will not have nozzle. Remove the top half of the caburetor and clean the 3 holes in the front of the carburetor base. One of the holes will be the fuel pump hole and the other two will be metering holes. Clean these out with a piece of tag wire. Reinstall the top half of the carburetor.
C. High speed adjustment is not correct.
This is for float style carburetors only.
1. Screw in the adjustment screw until finger tight. Now back it out 1 1/2 turns. This should be sufficient enough for the engine to run properly. This adjustment if for all Briggs float style carburetors and all Tecumseh float style carburetors. If the engine does not run correctly, let engine warm up for about 5 minutes. Screw the screw in until the engine runs erattic (lean). Then back it out until the engine runs erratic again (rich). Now turn the screw half way between and this should be good enough.