Pulsating is typically a sign of a lean condition.
Could be an air leak in the intake system.

The "brass nut" on the bottom of the carb is your Main Jet.
IF the holes in it were varnished up a bit, that would also lean it out.
You could remove it and carefully clean the holes.
OR
Dump a strong dose of carb cleaner in the gas tank and hope it cleans it out that way.

Also, use FRESH fuel. If the gas has been sitting over the Winter, it may be compromised.

This post was edited by bill_kapaun on Thu, May 23, 13 at 15:44

I took out the main jet nut and cleaned both the jets - bottom and the middle with a small wire. I'm not sure about the gas so I replaced the gas with some I have been using. Put some Seafoam additive in the gas and nothing changed. What should I be looking for with air leaks in the intake system? Thanks for the info.

I have the air filter off so as not to enter this into the problem.

Could a head gasket leak cause this problem or could there be a leak somewhere else?

Intake SYSTEM-
Carb mounting bolts, gasket etc.
Carb is 12 years old, so a worn throttle shaft is a possibility.

Does the carb. have an adjustments other than Idle RPM? IF so you might try to richen the mixture up some by turning 1/16 to 1/18 turn counterclockwise. Just note where the mixture screw was originally before you tamper with it so if that does not work you can turn it back to the original position.

I took the carb off and replaced the float pin, needle. Cleaned the bowl main jets again and hopefully cleaned the other jets also(sprayed carb cleaner down through the carb shaft). Replaced the gaskets. Started the mower up and started the surging again. I let it run a little while and then the surging smoothed out. However, doing a restart is almost impossible when the engine is shut down and restarting. Any more ideas? I'm going to check the spark lug when it cools down. Thanks again for ideas.

Did you put carb cleaner in all the holes around the carb? There is one hole that comes out in the center of the carb, just above the main jet? Have you checked for spark immediately after it shut down and wouldn't start? You could have a coil AND a carburetor problem.

Once running, it runs OK(starting fluid). Even now when it's cold, it won't start. I don't think it's a spark problem. I'm now wondering about the primer bulb. When pressed, there isn't any resistance - like fuel being pumped into the carb. It dosen't matter if I press the bulb 3 times or 15 times. Yes, I did force some carb cleaning fluid into the jet right above the main jet. There is plenty of gas coming from the fuel tank. I found that out when I took the fuel line off. .

If you remove the air cleaner, you should be able to see the fuel being primed into the carb opening. Usually the fuel will squirt out about 1/8" above the brass tube.

If you have the rectangular air filter on the front right side of the engine, the most common Briggs carb, there is a gasket behind the air filter housing. Sometimes a second gasket is installed, back to back, when the primer leaks too much air past the gasket, and no gas is primed.

Here is how to change the primer bulb:

The easiest way to change this type of bulb is to remove the air filter housing. Start by removing the air filter on this common air filter housing. The highlighted area shows the 3 screws to remove. Once removed, pull the housing straight out.

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Identify which type of primer bulb is used as there is one with a vent hole and one without. This type of air filter housing uses a bulb with a vent hole in the center. Note that the white clamping ring has beveled ridges and that they face outward at the top. These beveled ridges will lock into the housing.

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Use a pliers or similar tool to depress the beveled tabs that hold the clamping ring in place and move the primer bulb outward. Note the position of the tabs in the housing. When reinstalling the new primer bulb, you will have to line the clamping ring taps to align with the squared openings in the housing.

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Install the new primer bulb using a þâ socket. Align the tabs with the openings in the housing and push inward. It may require a good deal of force to get the tabs to lock in place. If they visibly donâÂÂt lock in place, the primer bulb will not be sealed and wonâÂÂt work properly, or not at all.

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On the back side of the housing, remove the old gasket, if necessary. Note the passageway for air under the gasket.

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Install a new gasket, if necessary. Note the small hole in the gasket that provides air to the carb to force gas up and out of the tube. With the air filter removed you should see gas squirt up out of the tube in the carb when pressing the primer bulb. Sometimes the air filter housing is warped and two gaskets are used. Do not overtighten the 3 screws when reinstalling the housing. Note on the top left of the picture the plastic nipple that gets reinserted into the breather tube coming out of the engine when you put the housing in place.

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I removed the primer bulb. It appears to be OK - no cracks, extra holes(other than the one that's supposed to be there) etc. But I will replace it anyway. I put a new air filter gasket (the one that you suggest might need two of). The hose that plugs into the filter cover that comes from the engine seems to be OK. I'll replace the primer bulb and see what happens. Thanks again nfor your expert help.

You can see the fuel being pushed into the carb. If you don't see it, something isn't installed right.

The new primer bulb didn't make any difference. With the beather hose hooked up to the air filter cover I don't see any gas coming through. I assume that the primer bulb creates a vacuum and sucks the gas through the breather tube into the air filter cover , then into the carb. When you say "something isn't installed right" are you talking about the carb installation?

The breather tube ONLY vents vapors from the engine's crankcase; no gas. The primer bulb ONLY forces a small blast of AIR into the fuel bowl of the carburetor thus forcing gas up the small emulsion tube in the middle above the brass bowl nut.

I noticed that when I slightly tilted the mower - gas tank up - that a small amount of fuel leaked out. Maybe I did't get a good seal on the fuel bowl when I replaced that O-ring. I didn't see where the fuel was coming from. Is there a way to test that the so see if the fuel is being forced up the emulsion tube? You mentioned that possibly the gasket on the filter cover maybe need two of the gaskets. Would that have anything to do with this? Maybe due to age the breather hose isn't getting a good enough seal to force the fuel (maybe needs replacing)?

The breather hose has nothing to do with priming.

The gasket and the primer bulb are the only factors.

If you look into the open end of the carburetor with the air filter off, you will see the short brass tube sticking up. If there is no fuel coming out of that tube when you prime, there is something wrong. See the aforementioned suggestions above.

I did all those things, gave up and brought it to the shop. Will report back when I get the mower back. I'm really curious about the problem.

Are you the only one who uses the machine? Any chance that someone else might have scraped a large piece of wood or a brick? A vibration introduced by a slight bending of the shaft might be seen as some as a pulsating problem.

OK, I blew it. I didn't get the new float blowl gasket on correctly. The pulsating quit after a very short warmup. Thanks again for all the forum help. I may have a electric Toro that won't start using the starter. The owner dosen't know for sure if the battery is even there, not charged etc. The SP dosen't work either. Should be fun.