# Speed adjustment on Briggs and Stratton



## riversr54

I have a push mower that is 3-4 years old, hasn't been used very much at all. It has developed a problem that I can't seem to figure out. Based on looking at current models at a couple of local stores, this seems to be a very common engine and carb configuration, but I can't seem to find any sort of model number or anything. My problem is that it runs way to slow. It has a speed adjustment that seems to have very little effect. Even in the wide open position the engine still runs very slow. I can't find any adjustment screws on the engine for idle speed or fule/air mixture. I tried to attach a phot here to clarify my problem but since I'm new on the forum it won't let me do that. Thanks for any help/suggestions.



riversr54


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## geogrubb

First, welcome to the forum.
Second, if you will post this in the 4-cycle repair it will get more attention, anyway;
The engine model, type and code should be on the metal engine shroud just above the spark plug. It sounds like the mower may have been pushed under a bush or something and the tab where the main governor spring is hooked got bent and needs to be bent back to it's original position. Have a good one. Geo


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## riversr54

*4 Cycle?*

I'm confused...is this likely a 4 cycle engine. (I'm not a mechanic) I thought all small engines like this were 2 cycle, but now that I think about it, maybe it is 4 Cycle since there is no fuel/oil mixture required.

As far as the throttle being bent...I don't think it is. I have full motion, I can rotate it back and forth, which seems to have no effect on engine speed. That's what is weird.


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## Deathrite

easiest way to tell difference. with 4-cycle you add oil to a different hole. on 2 cycle you mix it in the gas.


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## geogrubb

riversr54 said:


> I'm confused...is this likely a 4 cycle engine. (I'm not a mechanic) I thought all small engines like this were 2 cycle, but now that I think about it, maybe it is 4 Cycle since there is no fuel/oil mixture required.
> 
> As far as the throttle being bent...I don't think it is. I have full motion, I can rotate it back and forth, which seems to have no effect on engine speed. That's what is weird.


Try to find the model numbers, does the carb set on top of the fuel tank.

When you move it to full throttle the linkage should put tension on the governor spring(if it isn't broken or missing), if it doesn't put tension on the spring then the tab the spring hooks to needs to be bent to put tension on the spring. Have a good one. Geo


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## riversr54

*Checking*

Thanks for the info on the idler spring. I'll have to do some checking to see how that works. It all seems to be very loose, so maybe that is the problem. More later...


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## riversr54

*Carb Config*

The only thing like a model number that I can find is a Family Number. It is YBSXS.1581VA. Is that the model number? 

The carb sits on top of the tank. It has two springs, one about an inch long, small diameter with "slotted" hooks in each end so it has lots of play in it's tension. The second one is bigger, about two inches long and about 1/4 inch in diameter. It has some tension on it(not much) but has the most when the throttle position is wide open. I did a little comparing to current models at my local WalMart yesterday, mine looks identical to the B&S engines there. I think I can supply a picture now that should help.










Thanks again for any/all help and guidance.

riversr54


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## riversr54

*One other thing*

One other piece of information that might help diagnose my problem. I noticed that when I start it, it runs really fast for about 4-5 seconds, then slows way down and just limps along then. I can't tell but it sounds like the fuel mixture is wrong. Is there a way to adjust the mixture on this type carb?

riversr54


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## geogrubb

Your problem is not the linkage it's the diaphram.
You need to install a new diaphram kit, it is Briggs part # 795083 or old # 495770 also Lowe's has a kit #5083 which has the same parts.

Here we go;
Remove air cleaner, there are 2 bolts that hold things together, one on the front of the tank 3/8" and one into the block 1/2", remove these bolts, now "slowly" slide the carb/tank off the intake tube and breather tube, now tilt the tank in to release the throttle linkage and waalaa the carb/tank is removed. Check the intake tube to see if the “O” ring seal and plastic retainer are still on the intake tube, if so remove them and re-install them into the carb. Remove the 5 screws from the carb/tank remove carb(don't loose the spring) now spray all holes, cracks and crevases in both the carb and tank surface with brake parts cleaner, remove the main screen(looks like a thimble), now with a small screwdriver pry out the main jet(carefully) and clean it, check the “O” ring on the main jet for damage, if it is damaged it must be replaced, reinstall the jet, it can be difficult some times to get it to snap back in place(I use the rounded end of a screwdriver handle). Remove and clean the fuel pickup stem. Clean any junk/rust from the tank. Install the diaphram on the tank then the gasket(no goo or sealer) now carefully replace the carb(the spring will try to misalign the diaphram), tighten all screws a little at a time so as not to crimp the diaphram until they are all tight. Install the carb/tank in reverse order and you are done. If I missed something one of the real mechanics will correct me. Have a good one. Geo

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## riversr54

That will take me a few days to get to. I'll post my results later. Thanks for the help!


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