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Hi All, what would be the symptom of a bad breather valve on a Briggs Single Cyl 14-20hp size? I have a a 17hp 31C707 0230 that runs great until a drag is put onit either PTO or trans. Then it bogs down and pushes black smoke as if it running very rich. I can get it to recover by lowering the rpm, but it returns. There is a lot of carbon around the breather and between the valve cover and the spark plug and the whole underside of the engine cover. The spark plug boot was melted where it connects to the plug and the plug was fowled. I repaired the boot and changed the plug. Same symptoms.

I don't know if this is breather, carb, valve or head gasket related. Some advice would be greatly appreciated.

Pull your breather and see if the problem persists

Black smoke would indicate running rich. So could be a carb issue, but also make sure that there isn't gas in the oil which the cooking off of the fumes will cause similar symptoms. Bad head gasket or bad breather would create blue oil smoke.

If there is a lot of black suet around the spark plug/exhaust manifold to head connection could indicate a bad exhaust gasket, but could also be a symptom of a clogged exhaust and the resulting back pressure could lead to run issues.

Pulled the fuel tank and replaced everything to the carb. Pulled and cleaned carb. Coil has dragged the flywheel. Replaced the coil and set gap at 0.010". Set intake valve at 0.004" and Exhaust at 0.005" 1\4" past TDC. It was oil by the spark plug from the valve cover. Oil is good and no manifold leaks. Runs good only at low rpm. Smoke is not black as I thought, more lite blue-white. Doing compression and flywheel key checks tomorrow. If they are good, will change the carb. This has the white disc with the goofy O ring in it. The O ring around the fuel tube on the top of the disc is distorted. Tried one that is close in size, but wondering if fuel is not leaking by it. Mixture screw has no affect at any speed.

Well if it's running at all the flywheel key is not a problem, sounds like you're moving in the right direction , only runs at low rpm if the linkage is moving the throttle plate then you probably have a carb problem.

The replacement used carb ran good under load. I pulled the original Nikki carb apart and it shows signs of needing new rubber gaskets. What I was surprised to see is no jet in the center plastic tube. I'm used to seeing jets with bad O Rings. Is there suppose to be one? What would be the symptom of a bad jet O Ring?

Visually check that the choke butterfly opens fully
It is spring loaded open but the tiny spring is prone to breaking

Choke is good, Thanks

Freddie21 said:

The replacement used carb ran good under load. I pulled the original Nikki carb apart and it shows signs of needing new rubber gaskets. What I was surprised to see is no jet in the center plastic tube. I'm used to seeing jets with bad O Rings. Is there suppose to be one? What would be the symptom of a bad jet O Ring?

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Then you have lost the jet or who ever work on the carb last did. The jet is either 1.10mm or 1.11mm jet depending on the date code.

I rebuilt the carb and there was no jet. I properly installed a new one with new o-ring. It runs great for about 15 mins. I'm gonna pull the carb off and check it again.

Freddie21 said:

I rebuilt the carb and there was no jet. I properly installed a new one with new o-ring. It runs great for about 15 mins. I'm gonna pull the carb off and check it again.

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Is the fuel solenoid ok?

Yes, but I don't know how that would cause it to run rich.

With it being a Nikki the bowl gasket might have a bad place in it. They have to be nearly prefect, Otherwords, no nicks.. Also verify you installed the correct jet size.

Will have to check the jet. I don't know which one I put in. But, again, if the jet is wrong, I would think it would run crappy all the time not just when it gets hot. I wondering how the carb would fail with temperature. Unless, the mixture is good only when cool.

StarTech said:

With it being a Nikki the bowl gasket might have a bad place in it. They have to be nearly prefect, Otherwords, no nicks.. Also verify you installed the correct jet size.

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I despise those carbs.

I disassembled the carb and everything is correct, but it surging even at low speeds now. I rebuilt another Nikki using used parts and it runs well. Let it run at high speed for 15 mins and still good. I agree, I hate these carbs. I tried to convert a Walbro, but the throttle brackets are different. I couldn't swap as throats are different sizes. I've seen this done on UselessTube.

I was wondering if the breather needed vacuum to operate and if the engine would not run correctly if the tube was not connected, but I have been running this engine with a rebuilt carb and no breather tube connected and it runs fine. The tube is cracked at the air cleaner elbow. Should I fix?

Freddie21 said:

I was wondering if the breather needed vacuum to operate and if the engine would not run correctly if the tube was not connected, but I have been running this engine with a rebuilt carb and no breather tube connected and it runs fine. The tube is cracked at the air cleaner elbow. Should I fix?

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Buy a cheap Chinese carburetor and throw it on there. Use a spark checker to check coil(s). After 15 minutes when it starts running crappy, besides the smoke, does it hunt and surge? Spit and backfire, etc?

The main jet sits in the bottom of the white tube and is held there by the o-ring
Without it the engine will run fine until the governor allows the throttle butterfly to open fully when it will run very rich
There are 2 different types of gaskets for them
The Chinese repair kits do not fit , they are made for the Chinese clones that are smaller overall
I fail to understand why people have so much difficulty with them
The only problem for me is those bowl bolts that I am now replaceing with Allan headed cap screws so I can remove the bowl without having to remove the carb