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this started happening about two years ago so I replaced the carb and it seemed to clear up for a bit but started happening again. I also recently replaced the spark plugs and it seemed to run really well (higher reving) then it just acted up again. The kicker is that the mower runs fine until it is completely warmed up. Once it is hot the surging starts. If I cool the engine down by either letting it cool naturally or even if I hose it down, it will run smooth. I can't seem to figure this thing out. Any info on what to check next would be greatly appreciated.
Chuck

NEVER spray cold water on a hot engine.... It can be bad for electrical components and metals don't really like being taking from One extreme to the other, (hot to cold)

Surging is caused by a lean fuel mix ratio, meaning there is either TOO MUCH AIR in the mixture or NOT ENOUGH FUEL in the mixture.... This could be the result of a leaking carburetor/intake gasket or even a cracked intake pipe (manifold).. Or if the fuel line falling apart internally bits and pieces can flow into the carb and plug things up blocking fuel.
Post the engine model numbers so we can see what particular set up you have, should be stamped into the Overhead valve cover at the front of the engine.

I sprayed water on it as a test to see if it would affect the surging issue, and it did. I just think that its really odd that it only surges when it is fully warmed up (hot). I attached a pic of the label that you mentioned. Thanks again for for your help!!!

Scrubcadet10 said:

NEVER spray cold water on a hot engine.... It can be bad for electrical components and metals don't really like being taking from One extreme to the other, (hot to cold)

Surging is caused by a lean fuel mix ratio, meaning there is either TOO MUCH AIR in the mixture or NOT ENOUGH FUEL in the mixture.... This could be the result of a leaking carburetor/intake gasket or even a cracked intake pipe (manifold).. Or if the fuel line falling apart internally bits and pieces can flow into the carb and plug things up blocking fuel.
Post the engine model numbers so we can see what particular set up you have, should be stamped into the Overhead valve cover at the front of the engine.

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You have an air leak
get a trigger pack
Fill it with WD 40 or similar
Start the engine then spray the engine with the WD 40 till it runs different or starts to blow smoke
The last spot you sprayed should be where the leak is.

I sprayed starting fluid around the carb and the idle didn't change. This only happens when the engine is fully warmed up (HOT!). Otherwise it runs great. I can run it for roughly 10 to 20 minutes before the engine starts to surge. Just before it surges, you can hear the rpm drop slightly as if it was laboring to run. Thats also when I tried cooling it down with a hose to see if it affected it and sure enough it did. The engine ran better and stopped surging until it got hot again.

bertsmobile1 said:

You have an air leak
get a trigger pack
Fill it with WD 40 or similar
Start the engine then spray the engine with the WD 40 till it runs different or starts to blow smoke
The last spot you sprayed should be where the leak is.

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Yep. the engine gets hot and the crack opens up .
Spray cans do not cut the mustard and are highly likely to ignite
Do you think you will look sexy with no eyebrows ?

bertsmobile1 said:

Yep. the engine gets hot and the crack opens up .
Spray cans do not cut the mustard and are highly likely to ignite
Do you think you will look sexy with no eyebrows ?

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I always cringe, and laugh at the same time when someone says they use starting fluid for trying to find an air leak or prime a carb......that sh*t will blow your a** up!

Did the engine run better when you cooled the carb? Or the crankcase? How hot is the ambient temp? Have you checked for clogged cylinder fins? When it starts surging how hot is the carb to the touch?You might try to fabricate a heat sheild for the carb and see if that helps. What spark plugs are you using?

It runs better after I cool the crankcase. The weather has been in the mid 90's recently. I haven't been able to tell how hot the carb is getting. I will have to remove the covers and run it to check. The engine is pretty clean. I don't see and built up debris. The spark plugs came from craftsman and are a Briggs and straten plug. As far as heat shields go, it has them installed from the factory. Oddly enough, after I replaced the spark plugs (not long ago) it seemed to run great!!! It may have even reved higher. But something happened and it reverted back to its normal running condition. It was weird. I actually pulled the plugs to inspect them but they were fine.

Hammermechanicman said:

Did the engine run better when you cooled the carb? Or the crankcase? How hot is the ambient temp? Have you checked for clogged cylinder fins? When it starts surging how hot is the carb to the touch?You might try to fabricate a heat sheild for the carb and see if that helps. What spark plugs are you using?

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did you notice the color of the spark plug ends?

When i ask what spark plug i mean what is the number. The standard plug is probably a RC12YC. Air cooled OPE engines have no temperature regulation like an automotive engine. If the engine is running hotter than normal you may need to run a step cooler RC10YC plug.

They were so new when I installed them and then pulled them that they were still clean. I didn't notice anything other than that. I can look again tomorrow.

Scrubcadet10 said:

did you notice the color of the spark plug ends?

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I will check tomorrow. I will order new plugs as well just in case.

Hammermechanicman said:

When i ask what spark plug i mean what is the number. The standard plug is probably a RC12YC. Air cooled OPE engines have no temperature regulation like an automotive engine. If the engine is running hotter than normal you may need to run a step cooler RC10YC plug.

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That number isn't on the plugs!. Here is a pic. Do you know what the gap should be set to?
Thanks Chuck

Hammermechanicman said:

When i ask what spark plug i mean what is the number. The standard plug is probably a RC12YC. Air cooled OPE engines have no temperature regulation like an automotive engine. If the engine is running hotter than normal you may need to run a step cooler RC10YC plug.

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Champion RC14YC and RC14YC012 show as the champion plugs to replace the briggs plug.

Chucksrt said:

That number isn't on the plugs!. Here is a pic. Do you know what the gap should be set to?
Thanks Chuck

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That is the champion RC14YC. I would replace with RC12YC and see what happens. This is a step cooler plug

Should I still look to get a cooler plug?

Scrubcadet10 said:

Champion RC14YC and RC14YC012 show as the champion plugs to replace the briggs plug.

Click to expand...

Hammermechanicman said:

That is the champion RC14YC. I would replace with RC12YC and see what happens. This is a step cooler plug

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what hammer said

I just cut the lawn and for haha' I removed the front body cover (it has the headlights built into it) and it ran fine. Do you think that because its holding the engine heat in that it is causing the issue? It can't help that it's painted black either. It gets hot when it's not running. I think i will still switch to the cooler plug and see how it runs with/without the front cover.

Hammermechanicman said:

That is the champion RC14YC. I would replace with RC12YC and see what happens. This is a step cooler plug

Click to expand...

Chucksrt said:

I just cut the lawn and for haha' I removed the front body cover (it has the headlights built into it) and it ran fine. Do you think that because its holding the engine heat in that it is causing the issue? It can't help that it's painted black either. It gets hot when it's not running. I think i will still switch to the cooler plug and see how it runs with/without the front cover.

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I think you may be confusing the operating temperature of the engine and the spark plug temperature rating. This link may help if you are interested in the details. Summary is that a cooler plug may help if you are seeing preignition, but I don't think it will do anything for surging or overtemp.

Most likely the problem is boiling gas in the carb and making the engine surge. Changing the plug heat range will not make the engine run cooler but you need to match the spark plug heat range to the cylinder temperature the engine is running at. Spark plug electrodes need to run in the self cleaning temperature range which is approx 950 degrees F. If running too hot you can get preignition. If the engine is running on the verge of boiling gas in the carb the RC14YC plug may be too hot and need to run the RC12YC for the plug to operate in the proper range. Looking at the plug will tell you about what temp it has been running at.

Chucksrt said:

That number isn't on the plugs!. Here is a pic. Do you know what the gap should be set to?
Thanks Chuck

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Spark plug gap is .030

Chuck.
Start the engine and run it till it starts surging .
Slowly choke the engine
If the surging continues then you have an air leak after the carb venturi tube
If the surging stops then you have a fuel supply problem
I am yet to see a spark plug causing surging

Plugs won't cause surging but i have seen them run hot enough to cause pre ignition that makes the engine run very rough.

When it starts acting up, partially close the choke and see if it runs better.

If it still runs poorly,

Try adjusting the valves after it cools completely, one of them might have too little clearance.

I attached a picture of the plug earlier. Here it is again. It looks really clean. I tan take a better pic of the electrode if needed

Hammermechanicman said:

Most likely the problem is boiling gas in the carb and making the engine surge. Changing the plug heat range will not make the engine run cooler but you need to match the spark plug heat range to the cylinder temperature the engine is running at. Spark plug electrodes need to run in the self cleaning temperature range which is approx 950 degrees F. If running too hot you can get preignition. If the engine is running on the verge of boiling gas in the carb the RC14YC plug may be too hot and need to run the RC12YC for the plug to operate in the proper range. Looking at the plug will tell you about what temp it has been running at.

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Chucksrt said:

I attached a picture of the plug earlier. Here it is again. It looks really clean. I tan take a better pic of the electrode if needed

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The parts of interest are the center electrode, side electrode and tip insulator. I'm no engine guy, but from what I can see there's no carbon buildup on the plug (which would indicate the plug was too cold), and the insulator and electrodes aren't burnt (plug too hot). Check the gap, but to me it looks fine.

Chucksrt said:

I sprayed water on it as a test to see if it would affect the surging issue, and it did. I just think that its really odd that it only surges when it is fully warmed up (hot). I attached a pic of the label that you mentioned. Thanks again for for your help!!!

Click to expand...

That is the emission label and is of no help. On one ofthe valve cover should be the model, type, and date code stamped into it.

You may have a leaking head gasket or bad ignition coil since cooling the crankcase changing the engine operations.

Chucksrt said:

I attached a picture of the plug earlier. Here it is again. It looks really clean. I tan take a better pic of the electrode if needed

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A pic of the center electrode is what i was looking for. If the white insulator is a tan color the plug is runnig the right temp. If the insulator is white and the ground electrode is pitted or looks like it was sand blasted the plug is running too hot.

Hammermechanicman said:

A pic of the center electrode is what i was looking for. If the white insulator is a tan color the plug is runnig the right temp. If the insulator is white and the ground electrode is pitted or looks like it was sand blasted the plug is running too hot.

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The plugs are newer and when i pulled them for the kast pic that i did submit they still looked new. I can take a better pic if needed. It stopped surging when I completely removed the front hood assembly. Not sure if the black painted hood was heating up and or if the engine was heat soaked from the cover being installed? But I ran it for over an hour without the hood and it ran great.

The plugs you are running are probably ok. You most likely did not have enough air flow and the engine was hot enough to boil fuel in the carb. Taking off the hood allowed enough air for the engine to run cooler. Color doesn't really matter. When the outside temp drops 20 degrees probably can put the hood back on and not have a problem.

Hammermechanicman said:

The plugs you are running are probably ok. You most likely did not have enough air flow and the engine was hot enough to boil fuel in the carb. Taking off the hood allowed enough air for the engine to run cooler. Color doesn't really matter. When the outside temp drops 20 degrees probably can put the hood back on and not have a problem.

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I am having the same issues with my mower. Did this ever get resolved?

sqzdog said:

I am having the same issues with my mower. Did this ever get resolved?

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I've been driving it without the front cover ( the part with the headlights built into it). It runs great as long as I do that. I haven't experimented with cooler spark plugs ir anything else yet.

If it runs ok with the hood off don't worry about changing the plugs.