B&S sputtering

[blue262]

I have a Snapper SR140 33” with a Briggs & Stratton 12.5 hp I/C Quiet Rider
Model 286707 0136 0. I recently purchased it used to cut grass and the camp.

It makes an intermittent sputtering noise at any throttle position especially when the load increases. At idle it sounds like an intermittent “miss”.

I thought it might be a valve clearance issue but I verified both valves are in spec.

I opened up the Walbro carburetor and didn’t see anything wrong inside.

I videoed the sound at idle and higher throttle positions but I don’t see a way to attach videos in this forum.

Any suggestions on things to check that cause sputtering which increase with load?

 

[Tiger Small Engine]

I have a Snapper SR140 33” with a Briggs & Stratton 12.5 hp I/C Quiet Rider
Model 286707 0136 0. I recently purchased it used to cut grass and the camp.

It makes an intermittent sputtering noise at any throttle position especially when the load increases. At idle it sounds like an intermittent “miss”.

I thought it might be a valve clearance issue but I verified both valves are in spec.

I opened up the Walbro carburetor and didn’t see anything wrong inside.

I videoed the sound at idle and higher throttle positions but I don’t see a way to attach videos in this forum.

Any suggestions on things to check that cause sputtering which increase with load?

Take the Walbro carburetor apart and completely clean it. Drain old fuel and try again.

 

[Auto Doc's]

I have a Snapper SR140 33” with a Briggs & Stratton 12.5 hp I/C Quiet Rider
Model 286707 0136 0. I recently purchased it used to cut grass and the camp.

It makes an intermittent sputtering noise at any throttle position especially when the load increases. At idle it sounds like an intermittent “miss”.

I thought it might be a valve clearance issue but I verified both valves are in spec.

I opened up the Walbro carburetor and didn’t see anything wrong inside.

I videoed the sound at idle and higher throttle positions but I don’t see a way to attach videos in this forum.

Any suggestions on things to check that cause sputtering which increase with load?

Hello blue262,

First, are you using the correct spark plug and is it gapped correctly? I prefer to use Champion plugs on the older B&S engines like this. Gap at .030 feeler gauge

Your description also favors a partially clogged main jet and Yost tube passages inside the carburetor. These are areas you will not typically see when you open the carburetor up.

Before proceeding, the first place to check is for excessive throttle shaft wobble and play. If there is a lot of loose play, the housing is worn and sucking in stray air. The carburetor will need to be replaced. Aftermarket is about all that is available these days.

If the carburetor throttle shaft seems good, try the following cleaning method:

An easy (affordable) method for cleaning the entire carburetor is to use an old (scrap) saucepan and place ceramic saucer in the bottom. Place the carburetor on the saucer with the bowl and float w/needle removed. Fill with water to cover the carb and a few drops of Dawn or Simple Green cleaner. Bring the water to a soft boil. Boil it for at least 15 minutes then turn it off and let cool down good to room temp.

From there wash with clean water and blow our all passages to remove any hidden water. Do not place the carburetor in the oven to dry it.

Once you a certain that it is dry, reassemble and install the carburetor and give it a test run.

Keep us updated.

 

[StarTech]

Do not place the carburetor in the oven to dry it.

You mean not like I did my cordless home phone. I left it in the oven for about 6 hours with the oven on last Friday and was using it yesterday.

Still can get carb too hot in boiling water as that is at least 212F and if has any plastics they can warp. Ultrasonics is still the best way to clean a carb.

 

[slomo]

I don’t see a way to attach videos in this forum

Post it up on youtube. Link it here.

That is an old mower. Probably needs an entire fuel system clean slash refresh.

Meaning flush and rod out the fuel tank. Clean all the grass, bugs and leaves out of the tank. Make sure it flows with zero restriction out of the tank.

Install all new fuel lines, filter and shut off valve.

Verify you have 12 volts DC at the carb after-fire solenoid. Remove said solenoid checking the plunger extends/retracts when you turn the key on/off. I would snip the plunger at this moment meaning she will always start in the future. Use an inline shutoff valve prior to shutting down the engine.

As Auto Doc's said, boil clean the carb. Remove all rubber and plastic parts from the carb. Garage sale hot plate and cooking pot. Pine Sol and water on a low rolling boil for 45 minutes. Rod out all jets and passages. Blow out with compressed air. Float height set to level with the carb body where the bowl sits.

Pressure test the carb needle and seat at 7psi for 30 minutes.

Adjust the valves.

De-carbon the cylinder/s. Clean behind the valves too. Lap the head and block surface where the head sits.

CLEAN THE COOLING FINS and block under the upper engine cover.

 

[slomo]

Ultrasonics is still the best way to clean a carb.

Politely disagree. Not enough heat in my opinion. Heat is what releases the shelac varnish crud inside the carb. And a garage sale hot plate and some cleaner is way cheaper than an ultra cleaner. Use what you like.

 

[grumpyunk]

Depending on vintage, you may have a safety lockout that kills the ignition whenever it wants. Older models had a black plastic capsule/cylinder with several wires that grounded the magneto when certain switches were open/ closed. It fails in a miserable way, causing misfire intermittently, and aggravation when trying to start the engine.
If you have one, and it has failed, there is an expensive factory replacement available. For a fee. Or it may no longer be available and I do not know.
Long and short, if it fails, it will give similar symptoms. If disconnected, it will no longer try to stop you from mowing.
There is a push button switch that sits behind the gear selector slot for neutral. It is part of the circuit, as is the switch on the deck engagement linkage.
Of course it could also be the ignition (magneto) on the engine, some chafed wires grounding the magneto, and a few more.
tom

 

[RevB]

I have a Snapper SR140 33” with a Briggs & Stratton 12.5 hp I/C Quiet Rider
Model 286707 0136 0. I recently purchased it used to cut grass and the camp.

It makes an intermittent sputtering noise at any throttle position especially when the load increases. At idle it sounds like an intermittent “miss”.

I thought it might be a valve clearance issue but I verified both valves are in spec.

I opened up the Walbro carburetor and didn’t see anything wrong inside.

I videoed the sound at idle and higher throttle positions but I don’t see a way to attach videos in this forum.

Any suggestions on things to check that cause sputtering which increase with load?

re the carb.....you don't "see", you blow out passages with compressed air.