Diaphragm Carburetor Service

Learn how to service a diaphragm type carburetor, which are commonly found on many Briggs and Stratton Lawn mowers like the 3.5Hp Classsic and Sprint.

Tools/Parts Required 

  • Phillips Head Screwdriver
  • Socket Wrench - 13mm & 11mm
  • Flat Head Screwdriver

Step 1.

Begin by removing the air filter, then the petrol tank as shown in the video.

Step 2

Once free check your fuel tank for dirt and clean if necessary.

Step 3

Once removed clean thoroughly. Be careful when removing the gasket and diapharm not to lose the small spring and filter.

Step 4

Once the top is clean grab the tank and make sure any chunks of dirt or metal are gone. Carefully place your new diaphragm and gasket on the top piece and then reassemble.


  1. My victor law keeper engine 450series, 148cc, model 9T502’Type 2091 B1, Code08090952. The engine cuts out after about a half hour operation. The coil and spark plugwere replaced about a month ago and was working ok. Now it will run for about a half hour then cuts out. It will start again after priming the petrol again but only runs for a short time. I can start it again after priming it again but cuts out quickly. Prime start stop. I have stripped and cleaned the Carby but no change. Can you help please.

  2. Your series of tutorials are most helpful. Especially on “how” to do the particular tasks. The how is often more important than the what and written instructions are not always that clear. A picture is worth a thousand words!

  3. These tutorials are awesome. Getting an oood Classic 35 up and running, wouldn’t have had a hope in hell without your vids. Thank You!

  4. I seem to have to replace the diaphragm on my mower every year. Is this normal ? I use unleaded fuel with 10% ethanol (E10 fuel in Europe). Could the ethanol be causing the diaphragm to deteriorate ? Changing the old one (comes out “baggy” unlike a taut new one) cures the problem of running rich, using too much petrol, sooting up the spark plug and causing the engine to cut out after a few minutes running.

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