JeffN Posted October 20, 2003 Posted October 20, 2003 I've been having problems lately with the 8hp Briggs on my 728. When cold it will start and run with the choke closed and even with the choke open. But when the engine gets warm it will only run with the choke close or open the slightest bit. At times it will stumble and then I close the choke it will be ok for a bit and then stumble and I open the choke a bit. If I open the choke completely it will die. I am just wondering if an adjustment will take care of this or is it time for a carb rebuild. Any idea? Thanks.
rjgoth Posted October 20, 2003 Posted October 20, 2003 I will give 2 different possilbe solutions to your problem. With the choke closed there is a greater vacuum inside yoru carb, where the fuel is pulled through tiny openings inside the carb. As the choke is opened the vacuum reduces and in your case there is not enough vacuum to adequatly pull the fuel into the carb properly. This could be the problem IF there were no adjustments done to the carb previous to this problem. To fix this I would dissassemble the carb, and clean it. The second possiblity woudl be if you were making carb adjustments or if you have made adjustments. The closed choke provides a rich fuel mixture. When the choke is opened up the engine kills as a result of "starvation" of fuel. To remedy this you will need to open the main jet up on the carb to provide a richer fuel mixture so when the choke is fully open the engine will run. Once the engine is running with the choke open you can set the main jet on the carb, by leaning the mixture till you hear the engine start to miss. I then richen it back till it runs smoooth. That should be all it takes. Good question though, Ryan
slb04786 Posted October 20, 2003 Posted October 20, 2003 Or your carb is sucking air from somewhere other than the inlet. Check for leaks around the gasket between the carb and engine block. Are the screws holding the carb onto the engine loose? You can check for vacuum leaks with a propane torch (unlit). Crack the valve open a little and move the nozzle around the outside of the carb/engine gasket. If the engine suddenly revs up you have a leak there somewhere. Stan
Salthart Posted October 20, 2003 Posted October 20, 2003 Remove the in tank fuel screen. Replace any in line filters. It is slowing down the fuel flow. Thats why it runs fine when you cold crank, the bowl is full but the fuel won't flow fast enough to keep it that way once your running. Also, make sure the air vent in the cap is open. It can do the same thing.
PatRarick Posted October 20, 2003 Posted October 20, 2003 Another possibility is that it is not the carb at all. A bad spark plug, set of points, a condenser, or igntion armature (coil), can each give the same symptoms. I would begin with a new spark plug and an inline spark tester. Watch the condition of spark as the engine warms up. Pat
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