# B&S Sprint 3.75hp runs rough/misses



## engineer (Sep 15, 2011)

I have a sears pressure washer with B&S Sprint 3.75hp, it runs rough with incomplete combustion (odor). The spark plug is black & oily looking. For five seconds or so before it runs out of fuel it runs smoothly. Could it be running rich and if so how is the adjustment made?


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## duffer72 (Jul 23, 2011)

Most likely needs new gasket and diaphragm between carb and tank, normal on these, clean tank good while apart.


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## geogrubb (Jul 28, 2006)

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(not necessary if the fuel tank was clean). 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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## 30yearTech (Sep 14, 2006)

geogrubb said:


> Here we go;


You know, I can't look at a semi colon anymore, without thinking someone's winking at me....


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## duffer72 (Jul 23, 2011)

I agree with your directions but wouldn't have a novice pull the screen, jet or pick up, normally all I do I flush out tank, clean off pick up tube and throw in the kit. Question why do you use brake cleaner, for this type of cleaning I use cheap carb cleaner as all you are really doing is flushing it, rebuilding a float type carb is different.


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## geogrubb (Jul 28, 2006)

30yearTech said:


> You know, I can't look at a semi colon anymore, without thinking someone's winking at me....


30yr, if it makes ya happy, I will try to get rid of it, cause I sure ain't winkin at no guy from central Texas, lol. Have a good one. Geo


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## geogrubb (Jul 28, 2006)

duffer72 said:


> I agree with your directions but wouldn't have a novice pull the screen, jet or pick up, normally all I do I flush out tank, clean off pick up tube and throw in the kit. Question why do you use brake cleaner, for this type of cleaning I use cheap carb cleaner as all you are really doing is flushing it, rebuilding a float type carb is different.


I try to give as complete instructions as I can, the person doing the repair can determine those steps they think apply, if they question a procedure I send a picture if available, I have had new mowers where the hole in the nozzle had the plastic chad hanging. I use brake parts cleaner(usually walmart) because brake parts cleaner doesn't leave a residue. Pics below for jet/nozzle removal. Have a good one. Geo


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## 30yearTech (Sep 14, 2006)

geogrubb said:


> 30yr, if it makes ya happy, I will try to get rid of it, cause I sure ain't winkin at no guy from central Texas, lol. Have a good one. Geo


Was not upset, just my kids are always texting or emailing me and they are always doing the little faces with the colons : )  : (  or ; )  something like that, now I see faces in everything.....


I too use brakes parts cleaner on almost everything, makes a real good primer!


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