# Briggs and Stratton problems... cant figure it out! Any ideas?



## Ark (Oct 5, 2004)

I wonder if anyone here has Small Engine experience and can give me ideas on what to try.
We have a mower and a trimmer that BOTH have the same problem. The engines rev up and down constantly. A thorough carb cleaning did nothing to help. 
Nothing else seems to be wrong - it just goes RrrrrrrrrmmmmmmMMMMMMMM! up and down, over and over. :stars:
I hope someone who can think of something to try can help me out!
Thanks,
ARK


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## Windy in Kansas (Jun 16, 2002)

I'll let the expects tell you the problem, all I can offer is what my opinion would be from experience. Dirty air filter partially plugged, dirty spring on the governor, shroud has been off and the governor was not in the proper position upon re-installation.

Now we will wait and find out the correct answer.


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## sammyd (Mar 11, 2007)

If they have the newer carbs that are basically nothing but 2 pieces of plastic with a gasket between, buy the replacement gasket for 6 bucks or so and put it in.


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## Wis Bang (Feb 20, 2009)

gas to air mixture is changing, look for a place where air is being sucked in, like at the gaskets...


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## HermitJohn (May 10, 2002)

Modern small engines have carb set real lean for emissions reasons and no easy adjustment. So even slightest bit of crap in system or tiny air leak gives results you see. Only way to deal with it is to have fuel system spotless and sealed tight or you can drill out the jet a bit. At least they still have carburetors and not fuel injection.


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## BRYAN (Jul 5, 2008)

Probably high speed jet is clogged causing the surging. Some of these carburators have "blind" fixed jets with no access, sometimes, it is the idle jet. These are considered unservicable by the factory. When I was in the business, I cut a box full of carburators up with a hacksaw until I identified where to drill a 1/16 hole and use a needle to open the jet, without enlarging, it then reseal the hole with a stiff epoxy. A normal teardown and cleaning cannot access these jets. This is very common with the hybrid-pulsajet carbs by B&S, but it does happen to other types. If you can access the jet be very careful not to enlarge the opening.


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## ColumbiaSC. (Nov 25, 2005)

sucking in air


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## Ark (Oct 5, 2004)

Thank you all SO MUCH!! 

Still looking for the problem. SO frustrated. 

Wouldnt even began to know where to drill a hole... and cant risk screwing anything up....

The carb is spotlessly clean now. 

It is metal not plastic. 

Dirty spring on governor? It's clean, but how would that matter? Just curious. :help: Unless it was caked with mud? 

Gaskets look good, but maybe I should go ahead and order some new ones anyway..... 

For those of you who do a lot of small engine repair, where is the cheapest place to order parts? 

We've been using amazon and ebay whenever possible because they often have the best prices, although shipping from amazon will KILL you. There are some other places we get them from, but ebay is a favorite. 

Thanks again!


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## HermitJohn (May 10, 2002)

Its definitely a lean condition, not anything to do with governor spring. Its hard to guess when we have no idea of the particular Briggs engine and what carburetor it uses. Briggs used a wide range of carbs over the years. If you have no idea what you have, try posting a picture. 

When looking for parts, just do google for the particular part, great if you have a part number. Lot online stores and huge range of price for same part though you are never sure if part is OEM quality even if its labelled OEM.


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## marvella (Oct 12, 2003)

i know nothing about small engine repair. but i've been using a product called seafoam on the recommmendation of an HT poster. it cleans the entire fuel system. it is added to gas per the label instructions. you may have to pull it a few times to get it all the way through the fuel system. keep it running and it will gradually work it's way through. 

it has worked great for me. and a lot easier ($10/ can at the auto parts place) than drilling and taking stuff apart.


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## Ark (Oct 5, 2004)

Whatever the problem is, two different Briggs motors are doing the very same thing.
One of them is a 12F702 and here are pics of the carb. And I was just reminded that this one below does have new gaskets.


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## Ark (Oct 5, 2004)

marvella said:


> i know nothing about small engine repair. but i've been using a product called seafoam on the recommmendation of an HT poster. it cleans the entire fuel system. it is added to gas per the label instructions. you may have to pull it a few times to get it all the way through the fuel system. keep it running and it will gradually work it's way through.
> 
> it has worked great for me. and a lot easier ($10/ can at the auto parts place) than drilling and taking stuff apart.


Thanks for the idea. 
Wouldnt seafoam just be something that cleans? Which would be the same thing we are doing by cleaning out the carburetor the hard way? lol


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## retire2$ (Feb 12, 2003)

Did the gas come from the same can? What is the common thread. If you poured straight gas into the B/S engine and then used gas from the can to mix your 2 cycle mix and this gas had water in it or it was old this could be the common thread. My suggestion would be to discard this old gas from the can and let it dry and then go get new gas. Next drain gas from B/S engine by removing the bowl on the carb. Remove the float valve and using compressed air put the air in through the tank until only air is coming from carb. You can put a rag around the gas tank opening to force air through the fuel line and into the carb. Put float valve back in, attach bowl and fill with new gas. For the 2 cycle I would drain the fuel from the tank and then put a paper towel into the fuel tank to absorb any gas mixture. Now push the primer bulb until all the fuel is out of the bulb. After all fuel is absorbed remove and discard paper towel. Now mix up a new batch of fuel using the gas that you just purchased.


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## Ark (Oct 5, 2004)

retire2$ said:


> Did the gas come from the same can? What is the common thread. If you poured straight gas into the B/S engine and then used gas from the can to mix your 2 cycle mix and this gas had water in it or it was old this could be the common thread. My suggestion would be to discard this old gas from the can and let it dry and then go get new gas. Next drain gas from B/S engine by removing the bowl on the carb. Remove the float valve and using compressed air put the air in through the tank until only air is coming from carb. You can put a rag around the gas tank opening to force air through the fuel line and into the carb. Put float valve back in, attach bowl and fill with new gas. For the 2 cycle I would drain the fuel from the tank and then put a paper towel into the fuel tank to absorb any gas mixture. Now push the primer bulb until all the fuel is out of the bulb. After all fuel is absorbed remove and discard paper towel. Now mix up a new batch of fuel using the gas that you just purchased.


Thanks for the idea, but no, the gas is clean and new. The mower is one we are fixing (trying to!) for my dad, and the trimmer is one that was given to us "non-working" from someone who knows we do small engine repair. 

If we could just get this problem solved, the knowledge will most likley be quite helpful for future business! It's a learning curve, I suppose. :stars:


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## Harry Chickpea (Dec 19, 2008)

I dunno about dismissing the governor out of hand. If you can grab the lever that goes to the governor and manipulate it or hold it, can you make the engine run normally? If so, maybe there is some resistance that is holding back the normal action of the arm.

That said, idle jet issues seem like a strong possibility.


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## Ark (Oct 5, 2004)

*If you can grab the lever that goes to the governor and manipulate it or hold it, can you make the engine run normally?*

Yes, doing that does make it run normally!! BUT, the arm is loose as a goose. No resistance.


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## Old Vet (Oct 15, 2006)

Ark said:


> *If you can grab the lever that goes to the governor and manipulate it or hold it, can you make the engine run normally?*
> 
> Yes, doing that does make it run normally!! BUT, the arm is loose as a goose. No resistance.


replace the spring for the Governor. It is supposed to have some resistance on it. If you can hold it and make it run smooth the spring is not either hooked up right or is so loose that won't control anything until you get way to fast or too slow.


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## Harry Chickpea (Dec 19, 2008)

Yeah, sounds like it could be a weak or damaged spring. Still not ruling out the idle jets, but I'd replace the spring first and see what happens.


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## HermitJohn (May 10, 2002)

You would think I could at least find a picture of a 12F702 with google, but just find links for parts. Is it OHV or flathead? From the parts its 5hp but thats about it for info I could find.

Unless spring is stretched to point it isnt doing its job, just highly unlikely to be governor spring especially on two different engines at same time. Holding gov lever without engine under load means little, you are just basically holding the throttle plate on carb in one position, like holding throttle open on car carb while car is parked, doesnt prove much of anything except the engine will run and its getting enough gas to run without a load on it. On your small engine its probably just lean enough to cause the constant hunting by gov. Since I dont know what kind of gov this 12F702 has (fan type or internal), cant say much more. Governor arm isnt supposed to be hard to move. Its goal is to keep engine at constant rpm under load. So the more load, the more it opens the throttle plate. And this governor is capable of changing the throttle position far faster than you could ever do manually. If its hunting when engine isnt under load, thats telling me you have a lean condition. I know nothing of carburetors with hidden jets the fellow above mentioned though wouldnt surprise me with other stupid EPA induced design I've seen. Is a good flow of gas getting to the carb? In other words with fuel line pulled off at the carb are you getting good flow out the line? Then with line hooked up but bowl off the carb, is there a good flow gas coming down to fill the carb bowl? For all I know it could be some hidden jet but I've never seen such, still think its restricted flow to carburetor if you have thoroughly cleaned the carb, meaning soaked the disassembled carb in can of carb cleaner overnight and blown out all passages you can see in in the carb with either compressed air or aerosol can of carb cleaner.

Here a new carb for $40 for your engine (found it while looking for picture of your engine): http://www.smallenginesuppliers.com/shop/html/pages/products/Briggs_Stratton_Carburetors3180.html Thats one way to eliminate the carb from being possible problem. I would however first make sure there is plenty of gas getting to the carb bowl on your current carb.


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## Ark (Oct 5, 2004)

The trimmer DOES seem to run better with a load on.... but I am not sure about the mower. 

Thanks all for the help - I will try to answer all the questions, and hopefully wont miss any. 

Even though we have two machines with the same problem, it may just be a coincidence rather than a common cause. We got them from two different people and they arrived with this problem. 

When I said the lever arm is loose as a goose, I meant that you can move it freely when you take the spring off. When the spring is attached it does seem to have the proper amount of resistance. The spring looks as if it is properly tightening and loosening as needed. 
_
Is a good flow of gas getting to the carb? In other words with fuel line pulled off at the carb are you getting good flow out the line? _ *Yes.*


_Then with line hooked up but bowl off the carb, is there a good flow gas coming down to fill the carb bowl? _ *Yes.*



_For all I know it could be some hidden jet but I've never seen such, still think its restricted flow to carburetor if you have thoroughly cleaned the carb, meaning soaked the disassembled carb in can of carb cleaner overnight and blown out all passages you can see in in the carb with either compressed air or aerosol can of carb cleaner._ *We did soak it overnight, but will try blowing it out today - hadnt done that. Dont have any compressed air on hand, but do have the aerosol can of carb cleaner. Thanks for the idea. 

This is bugging DH so much - to not be able to fix these two machines. So, thank you ALL so very very much for all you've done to try to help, all the suggestions, and even the googling!! :goodjob:
*


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## retire2$ (Feb 12, 2003)

Have you priced a new carb? I think that would be my next step. Then I would decide if it was worth the cost of fixing or being used for parts.


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## solidwoods (Dec 23, 2005)

The butterfly shaft may be worn and allowing air to pass by into the carb.
jim


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