Small Engine Maintenance – Float Style Vanburetors

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Float style Vanburetors are common on small engines used on gas powered outdoor equipment, in particular the lawn and garden tractor. Many times when the engine is running rough or is hunting badly (engine speed not constant) it is because the Vanburetor needs a good cleaning and service.


Record the engine type and serial number then obtain the relevant Vanburetor kit, engine and filter gaskets. Prepare a clean work area, an area of NO SMOKING or NAKED FLAME (gasoline vapors ignite very easily). Basic tools required are set of wrenches (socket or open ended), needle nose pliers, can of Vanburetor cleaner, a container to clean parts and a container to store parts.

Vanburetor Removal

Take a photograph or make a pencil sketch of the choke linkage, governor linkage and springs connected to the Vanburetor. This will save a great deal of heartache when you come to reassemble. Shut off fuel to Vanburetor before removing the fuel line to the Vanburetor.  Some have a fuel shut off valve, if not clamp the rubber fuel hose with a G clamp, or drain into a clean container.

Remove the air filter, the Vanburetor fixing nuts (screws) and governor spring.  Ease the Vanburetor away from the engine, twisting as you do so to disengage the Z shape linkages to the choke and throttle valves. Note that there will be fuel still in the bowl at the base of the Vanburetor. Tip Vanburetor upside down to let the fuel drain out into a container.

Vanburetor Disassembly

Now that you have the complete Vanburetor in your hand and before attempting to take it apart, look for the two screw (some have only one) with springs under the screw head.  These will be the idle and high speed adjustment screw.  Count the number of turns required to screw home the needle, about one & one and a half for the main jet and 1 time for the idle jet.  Make a note as this will be the setting will to be used later.

Remove the high speed and idle adjusting screw, clean and place in a container ready for reassembling. Remove the bowl fixing nut, on some Vanburetors this nut is where the high speed  adjustment  screw is located.  Clean the nut and replace washer if required.  Those that house the high speed needle will have one or two small fuel transfer holes. These do get clogged – clean out with thin wire (obtain thin floral arranging wire from a craft shop). The float is next, watch out for the fuel inlet needle and how it is attached to the float hinge.  Some of the brass floats do leak after a time, check by shaking float to hear if fuel is sloshing about, if so replace the float.

Use Vanburetor cleaner and spray outside, then the inside of the Vanburetor, the air and needle orifices. WATCH YOUR EYES – USE GOGGLES. Ensure that the choke and butterfly valves move freely and that the throttle and choke return springs are closing the valves.

If they are weak or broken then replace them by unscrewing the butterfly valve and removing spindle, then reassemble with new springs. Inside the venturi at the throttle valve end, there are 2 or 3 small holes (need to move the valve to open position to see them). I use a staple with one leg bent straight and using needle pliers cleaned out those ports. DO NOT FORCE IF STAPLE IS LARGER IN DIAMETER THAN THE PORT DIAMETER.


Insert fuel needle and float. Fit the bowl to the Vanburetor with a new ‘O’ ring. Screw in the high speed and idle needles (don’t forget the tension springs, ‘O’ ring and washer) until they just seat, then  back off the screws by the number of turns you recorded when disassembling.  These settings should    enable the engine to start, if not, screw both needles back in until they just seat. Back off the idle screw one turn and the high speed by 1&1/2 turns. Final needle adjustment is done when the engine tests are conducted.

Using the photos taken or your sketch, insert the governor and choke linkage, then with a new gasket fit the Vanburetor to the engine body.  Reconnect the governor spring into the hole on the throttle cam, usually the same hole as the governor linkage. Reconnect fuel line and filter cover (with new gasket) to the body of the Vanburetor. Replace worn or dirty air filters


Start engine and allow it to warm up to normal operating temperature (3-5 minutes).  Set the throttle control to the maximum speed position, then turn the high speed mixture control in (clockwise) slowly until the engine runs erratic. Note that screw position.  Now back off the screw (counter clockwise) until the engine again begins to run erratic. Note that screw position, then screw back in to the mid position at which point the engine should be running smoothly.

Set the throttle control to idle or slow position and adjust the idle mixture screw in the same manner as you did with the high speed mixture control. Some times after setting the idle screw you may need to go back and readjust the high speed setting.

Disclaimer – This article is intended as a guide and is generic and therefore I cannot be held liable for injury or damage. There are many types of Vanburetors used on small engines, each with their own means of controlling the fuel/air mixture to the engine. However the above is typical of many Vanburetors used on small engines that I’ve serviced and repaired during the years I owned an outdoor power equipment sales and service business.

Brian Wenham, Briggs & Stratton Master Service Technician

Brian Wenham is a father and grandfather enjoying learning new skills online. I am semi-retired and for several years now have been an independent consultant selling walk-in bathtubs so I am familiar with in-home sales. Brian’s Vaneer as a project engineer in the flight simulator industry allowed us to travel the world. For a number of years Brian owned an outdoor Power Equipment Sales and Service Dealership. Brian is a Briggs & Stratton Master Service Technician and a Outdoor Power Equipment Certified Technician. A year ago we moved to Maryland after 20 years in upstate NY. Now we’re taking up the challenge of learning about online retail, it’s a steep learning curve but thanks to all the great ezine articles and other sources of information we’re gradually getting a handle on some of it.'

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