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briggs and stratten 3.5 HP starts and dies


woodfish's Avatar
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05-28-11, 09:01 PM   #1  
briggs and stratten 3.5 HP starts and dies

Got a new power sprayer (Craftsman) with B & S 3.5 HP. 15 hours of no worries last summer 2010 and fall, hauled it out for spring cleaning today 2011, new gas, good oil level, plug in good shape, air filter clean...cranked it up, started fine then started going up and down in rpm, finally dies after about 45 seconds. Pulled the rope, started great dies after 15 seconds, so it goes for the next 15 minutes, let it sit for 10 minutes, starts up and the same exact mode, up and down rpm then dies after 40 seconds, then start and die 15 seconds. one hour later i give up.

 
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05-28-11, 09:57 PM   #2  
Kind of sounds like the carburetor diaphragm needs changing.


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05-29-11, 08:24 AM   #3  
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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05-29-11, 09:31 AM   #4  
Thanks, before i dig in it important to note that there is no black smoke and this is a new engine with only 15 hours on it, does that change your analysis?

 
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05-29-11, 11:17 AM   #5  
My mistake it is a 6.75 HP Briggs Fast Start, does that change your diagnoses?

 
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05-29-11, 12:43 PM   #6  
Posted By: woodfish My mistake it is a 6.75 HP Briggs Fast Start, does that change your diagnoses?
A 6.75 doesn't have a diaphram carb, however, still sounds like it needs the carb cleaned, post the engine model, type and code usually stamped in the metal shroud just above the spark plug so we can find what carb it has. Have a good one. Geo

 
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05-29-11, 08:01 PM   #7  
model number 580-752191
I got i running today, by manually operating the air vane, it was touch and go as long as I had a wide spread spray valve but when i switched to the high pressure head to get the high points it wanted to to stop. I would say it ran at half speed most of the time despite the throttle lever on high. The only time it ran on high speed was when i manually operated the air vane or when i stopped spraying. When i would press the trigger for pressure it would either die or almost die and I would get a low pressure spray. I did mange to keep it running though it died several times especially when i tried to run the high pressure jet for high spots. Ran through a tank of gas in a hurry with crappy up and own pressure. once again this was all predicated on my manually manipulating the air vane level to get it running.

 
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05-30-11, 08:12 AM   #8  
The nut that holds the bowl on is the main jet for that carb and is probably dirty or has a varnish buildup from leftover gas. It has holes across the bottom and down through the center. Be very careful when you remove the airfilter housing, the gasket between it and the carb is part of the primer circuit and if you damage it, it must be replaces or the primer will no longer prime. Refer to the pic below for the main jet. Have a good one. Geo


 
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05-31-11, 08:55 PM   #9  
You were on the money, used a sewing needle to clean the jet holes, got it running, good pressure but still does not hold the highest pressure, so much better than it was, thank you, next time remind the novice to make sure there is no gas in the tank when you take the bowl nut out....what a mess in the garage, I am grateful for your patience and help.

 
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