This problem can occur if the carburetor fuel-pump diaphragm is worn or damaged. As with all carburetors, it is especially important to use fresh, clean fuel with Pulsa-Prime carburetors. The use of stale fuel or fuel that does not meet Briggs & Stratton's recommendations can cause rapid deterioration of the diaphragm material. In most cases, this older fuel can be added to your car's fuel tank with no harmful effects.
For a typical example of how an engine sounds while hunting and surging, please listen to the following:
NOTE: Briggs & Stratton engines are not designed to run on E85 fuel. E85 is a blend of 85% ethanol (alcohol) and 15% gasoline, which is not compatible with most engines intended to run on regular gasoline. While alcohol is an excellent octane booster, it delivers less power, having an energy value of only about 77,000 Btu per gallon versus 114,000 Btu for regular gasoline. E85 also demands a different fuel-to-air ratio to burn efficiently, requiring specially calibrated carburetors. Further, specially designed fuel system components are required to withstand the high alcohol concentration found in E85.
The use of Briggs & Stratton Advanced Formula Fuel Treatment & Stabilizer is recommended, as well as purchasing the gasoline "in season" (gasoline is mixed differently in the Fall than in the Summer).
This stabilizer can be added to the fuel when filling the engine with gas, or it can be mixed with the proper amount of fuel in a gas container for future use. Keeping stabilized fuel in the engine during storage will also prolong the pump diaphragm’s life by keeping it moist.
If the diaphragm needs to be replaced, the new diaphragm must be positioned on the fuel tank and the gasket must be placed on top of the diaphragm correctly (straight/flat). The carburetor mounting bolts should be then tightened in correct sequence to 17-20 inch lbs. (see diagram
Complete repair/servicing information for this model engine is located in the Single Cylinder "L" Head Repair Manual(Part Number-270962).
By viewing your engine model's Illustrated Parts List you can obtain any engine part numbers you may require. Simply enter your engine Model and Type numbers into the search fields located near the top of the Illustrated Parts List look-up page.
Engines used in lawnmower applications usually have these numbers stamped into the blower housing or a few inches above the spark plug. Depending on the type of engine shroud used with your mower, the engine numbers may be covered. It may be necessary to remove this shroud in order to locate the Model, Type and Code. Please visit the Identify Your Model Number
for help in finding the engine’s numbers.
If the above does not improve engine performance, or you are not sure how to perform this maintenance, please consult a Briggs & Stratton Authorized Dealer located in your area. Your Briggs & Stratton Authorized Dealer has all the information relating to Briggs & Stratton warranty information, replacement engines, short blocks, parts, pricing, service/repair, specifications, etc.
NOTE: Please read and abide by any applicable Safety Information (PDF) before performing any engine work. This information is not meant to take the place of work performed by a Briggs & Stratton Authorized Dealer. Terms and Conditions apply to all of our information provided on this website. Always be sure to read and understand your engine Operator's Manual.