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I have had it sitting in my garage for three years, stopped using it because I noticed the pulsating / surging and never had it fixed. Just changed oil, oil filter, gas filter, flushed gas tank and cleaned carburetor. It has brand new gas as well as battery, spark plug and fuse holder.

I can see the arm connected to the inner butterfly (closer to the engine) moving in an open / shut position about 2x/second when the engine is running...if I can even get it running. I am curious as to whether or not this could be a fuel system issue even though I cleaned everything out. I'm leaning towards to carburetor or the governor, but I honestly don't know what I'm looking for at this point.

The carb solenoid seemed a little weak when I push it down and release it, although it pulls down immediately under a 9V battery.
The air filter (tube kind) looks perfectly "white", but inside on the end of it looks like it has some kind of sticky residue which smells like gas.

I wanted to upload I short (4MB) MP4 video, but this forum will not allow it. I think everyone gets the general idea, I can email the video if anyone wants to see it.

I have already sank about $90 into this and probably another $50 forthcoming for a new carburetor. I'm hoping that people who are more experienced might recognize the cause or offer some advice. I'm new to small engine repair(s), so any advice at all would probably be useful. Thanks!

Hi 1chris1,

Welcome to the forum. Thanks for providing the details of your problem and the appropriate engine numbers.

The first thing I advise is never mess with the governor adjustment unless have had to replace a sump gasket due to leak. A governor simply controls the engine from running wide open above the designed RPM limits, that is it, plain and simple.

Next, how did you clean the carburetor? Just blow some spray on the parts and down the throat of it and call it good? Inside the carburetor there are very tiny passages that get gummed up, especially with old fuel being left in it and then run that way. Only non-ethanol fuel will keep for about a year. Ethanol blend fuels only keep a few months regardless of what stabilizer you use. I have tested and tried them all over the years.

An aftermarket carburetor is not advised and may introduce a whole new set of problems to contend with.

Has the valve adjustment been checked? Briggs engines are critical about proper valve adjustment checks about once a year.

This engine has 2 possible carburetor types on it. Here is a link for you to refer to for any parts. They also have parts for the rest of the machine:

It currently has about a half a tank of gas I bought a couple of days ago, with no additives.

I took the carburetor apart and cleaned out the bowl, which had bad smelling old gas with a greenish color and green deposits on the bottom of the bowl. I scrubed the bowl out with a steel brush and Stabil carb & choke spray, and sprayed everything down generously. Everything looked very clean, but I did not run wire through the needle in the carburetor. I used compressed air to dry and reassembled.

Since I had it running for about a minute today (surging or pulsing), I haven't been able to get it to run again. I talked to my buddies at work, one of them told me this is called "surging" or "hunting" because the engine is trying to find the correct RPM's. Another one recommended removing the air tube just to see what would happen, and sometimes air issues look like fuel issues and vice versa.

Because of the fact that it won't start now at all I'm hoping it's a blockage in the carburetor. I was honestly considering ordering one of those cheap aftermarket ones, so thank you for steering me away from that. Do you think I should just order a new OEM carburetor and see what happens, or do you suspect there might be another issue going on? I'm really starting to think it needs professional service. Thanks again for your help!

Here is a YouTube video I made today of the engine:

Hello 1chris1,

The thing I would do is pull the carburetor back off and spray through the main jet with (only) Chemtool B-12 carb spray with the straw attached (wear nitrile mechanic gloves), let it sit for about 15 minutes, then repeat 3 times, wait between each spraying. A fine steel tenor instrument string is great for cleaning the jet also, if you can find one. Do not use a toothpick or soft material that can lodge in the jet.

This method will give the carb spray time enough to soften and dissolve the old fuel resins that are blocking the fine passages up inside the emulsion tube of the carb and the main jet.

Be careful with this carb spray and avoid letting it hit you in the face or eyes. That stuff stings on the skin and in eyes.

When you start it up, choke the carb by hand with a shop rag quickly a couple of times to create a high suction. That will help pull any remaining softened debris out of the fine passages usually. (Old school carburetor trick that I have used for many years.)

Hope this helps you.

1chris1 said:

Here is a YouTube video I made today of the engine:

Click to expand...

That is blocked carburetor air bleed passages. Air has to balance in the carburetor as fuel is being drawn in. If it does not, surging occurs.

make sure the air cleaner to carburetor gasket is in the correct position, it has a carburetor hole it has to line up with.

Thanks again Auto Doc for your response, I'm going to try some B-12 Chemtool spray tomorrow and do a deeper cleaning. When you say choke it with a rag, I'm assuming you mean block the airflow momentarily? (Not sure if that even applies now since you have seen the video). I have a Nikki carburetor and am not sure if those air bleeds are an internal component, but hopefully I can get those cleaned tomorrow. I found some YouTube videos from BaldEagle242 about Nikki carburetors diagnostics / rebuilds, I watched only the rebuild one tonight. The small o-ring on my fuel intake valve got pinched it yesterday and the carburetor flooded, and I redid it this morning. At the very least I should rebuild mine and change the seals.

Hi 1Chris 1,

Check for free-flowing fuel from the fuel tank to the carburetor. Remove the line at the carburetor. Use a good size container and leave the fuel tank cap in place. See if fuel flows freely, or it has trouble flowing. If so, check for trash caught in the fuel tank exit nipple or a gas cap not allowing in atmospheric air in the tank. If it has a tank top vent line with a check remove it and see if it runs better. The check valves are known to stick closed with age.

Next, leave the air cleaner elbow portion off and use some spare nuts as spacers to hold the carburetor to the intake. And yes, you can use a rag to momentarily choke with a rag or your fingers it to create an instant suction effect.

As you gradually choke it by hand, will it begin to run smoother? If so, passages are clogged in the carburetor, or the intake to head seal is leaking.

You might end up replacing the carb, because these Nikki carburetors are not good about resealing when taken apart.

Have you actually unbolted the intake from the head to check the sealing gasket there?

Hypothesis:

Just to give you a sense of what is happening, think about a "water cooler effect". A person hits the lever to fill the cup with water. But what happen at the same time? Air is drawn in past the exiting water and burp happen in the water container jug happens.

In the carburetor, if air cannot get into the top of the fuel bowl as the engine is drawing in the fuel, this same effect takes place. The engine is "burping" the air/fuel mixture basically indicating there is not enough air/fuel mixture to satisfy combustion.

Hope this is not hurting your head yet. LOL

I went to several auto parts stores today looking for the Chemtool B-12, no luck (they only have the injector cleaner). I had to settle on Pyroil... it's a non-chlorinated methanol base just like the B-12 and came with a straw.

I sprayed through the holes in the jet and all the inlets and outlets I could find in the body. Everything was pretty clean to begin with. There is also a small metal piece in the middle of the float assembly, I sprayed that out too. I'm not home at the moment, but I'm going to spray it down again a few more times when I get home. I made a video of the inside of it, as well as the fuel line which doesn't appear to be obstructed.

I'd highly recommend replacing that bowl gasket and little O ring, if they fail, they will overflow your carburetor
Briggs and Stratton 698781

Fuel flow looks good from the line, make sure to check the carb fuel inlet nipple and float seat are for any trash lodge in them. It only takes a small flake of debris to create headaches when it comes to carburetors.

I noticed the idle air screw has not been removed (Black restrictor cap on the side). Take a pair of side cutters and cut down alongside that black cap. Get the cap off and carefully screw the metal needle inward to count how many turns until it stops lightly.

Then remove it and blow through the passage and make sure it is cleared out. Install the needle fully seated and count the turns to get it back close to the original adjustment setting that you counted earlier

Once everything is cleaned and dried, reassemble it and see what happens. You may have to adjust the needle out or in slightly, but it should run much better without all the surging up and down.

Scrubcadet10 said:

I'd highly recommend replacing that bowl gasket and little O ring, if they fail, they will overflow your carburetor
Briggs and Stratton 698781

Click to expand...

Thanks for the part number, I'm going to order new seals and keep the carburetor. The little o-ring still holds for now, it got pinched when I left it up in the metal assembly. I then ran it like that immediately after, and the pulsating in that video was identical to what it was doing 3 years ago. The next morning there was a small puddle of gas underneath the air elbow as I also forgot to reconnect the small tube that goes from the engine straight to the bottom of the air tube. (I probably wouldn't have noticed it otherwise). I cleaned the air tube really good, reassembled the carburetor & it has never flooded again. Trouble is right after that first run it won't start again. So I am starting again at square one tomorrow with the air intake elbow off, but I have a feeling I might have engine trouble at this point.

Auto Doc's said:

Fuel flow looks good from the line, make sure to check the carb fuel inlet nipple and float seat are for any trash lodge in them. It only takes a small flake of debris to create headaches when it comes to carburetors.

I noticed the idle air screw has not been removed (Black restrictor cap on the side). Take a pair of side cutters and cut down alongside that black cap. Get the cap off and carefully screw the metal needle inward to count how many turns until it stops lightly.

Then remove it and blow through the passage and make sure it is cleared out. Install the needle fully seated and count the turns to get it back close to the original adjustment setting that you counted earlier

Once everything is cleaned and dried, reassemble it and see what happens. You may have to adjust the needle out or in slightly, but it should run much better without all the surging up and down.

Click to expand...

Someone told me to do take the black cap off and clean under there on TractorForum, I didn't understand the whole procedure with the adjustment screw -- thanks again for the detailed, step by step instructions as it is really helpful for newbies like me. I'll start there tomorrow and report back if I can get it running again or not.