Briggs V-Twin Surging Issues

Craftsman Garage

Craftsman Garage

Well-Known Member
I'm currently working on a Briggs 40N777-0027 Vtwin, and it has a persistent surging issue. This is one with a single barrel carburetor. I initially replaced the old carb with a aftermarket one and it ran okay at low speeds but anything higher than idle it seems it would run and then die and repeat every 3 or so seconds. It would catch itself and doesn't turn off but just surges like this. I figured I would try rebuilding the old OEM carburetor and it runs even worse. What am I missing here? I cleaned the heck out of that original carburetor and all of the seals and everything were brand new. Now I've got 2 carbs and a pile of new parts. What do I do here?
 
Have you checked the fuel flow from the tank? There could be crud restricting the flow. It sounds like you'd have done that, buy you didn't say anything about it.
 
Since this is a single barrel Nikki while it is surging slowly apply the choke. It should smooth right out before it starts being too rich. If so you have a high idle circuit problem and the carburetor will need a slight modification.

I done had two carburetors with this problem this year.
 
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Mark and StarTech have some good advice for you. Little more below.


Step 1 - squirt some 2 stroke gas into the carb bore. If she fires off then dies, you just confirmed 4 things. She has air, spark AND spark at the correct time, enough compression to run and a LACK of fuel delivery. One simple test will tell you a lot about your engine health.

Read that again.

That is mower troubleshooting 101.

Step 2 - pull the fuel hose off AT the carb inlet. Should have a solid flow of fuel here. If your engine has a pulse fuel pump, CRANK the engine for this test. If you have a trickle or no gas coming out, red flag. Drain into a clear jar looking for water and trash.

IF you have a fat solid fuel flow AT the carb inlet, confirms
1.fuel tank cap IS venting
2.good flow from tank to carb inlet. Includes all hoses, filter and possible shutoff valves.
 
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Vacuum leaks and or incorrect or missing carb intake gaskets. Torn or installed backwards. Heat insulator shims missing. Some Honda's if you put the gaskets on backwards she won't run. It will block a vent hole off.
 
Well I got a chance to work on it and I looked at a few things. I noticed that there wasn't much fuel flow and narrowed it down to the paper filter really blocking the flow. I replaced it with a typical screen filter and the flow looks much better how it usually is. I also tried putting the OEM jet on the amazon carb (what I usually do when I buy new carbs) and it runs very good now. It only smells a little bit rich at idle but everywhere else it runs great.
 
slomo said:
That is a pilot circuit IF your carb has one. Could be clogged or improperly adjusted. Could be a needle issue too. Pull the oil stick and smell for fuel. If so red flag.
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From what I can see, the only adjustment on this is the idle speed. The welch plug on the top only covers the idle circuit holes.
 
What about my comment on "Could be a needle issue too. Pull the oil stick and smell for fuel. If so red flag"?
 
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