My older Craftsman edger is equipped with a 3.5 hp B&S engine. It had been surging at no load. Bought a genuine B&S carb kit and installed it. Problem is better but not gone. This carb doesn't seem to have a mixture adjustment screw. Based on my Googling I suspect it has a "pilot jet." The kit included mixture adjustment screws for various models but nothing that fits my carb. Has anyone here ever come across a carb like this?
Two things I would check. Did the kit come with a new pump diaphragm? Did you install a new gasket between the carb and tank. Remove the carb a see if the small auxiliary tank is full of fuel. If not the seal may be compromised and leaking. This will not allow a steady amount of fuel in the auxiliary tank.
Two things I would check. Did the kit come with a new pump diaphragm? Did you install a new gasket between the carb and tank. Remove the carb a see if the small auxiliary tank is full of fuel. If not the seal may be compromised and leaking. This will not allow a steady amount of fuel in the auxiliary tank.
Yes, the kit included a new diaphragm (fuel pump). Yes, a brand new gasket between the carb and tank. I would like to avoid taking the carb off again. It's a big pain in the behind.
I would check the carb intake manifold to block. Briggs uses really thick gasket like 3/16" or thicker there. Chinese Amazon/Ebay carbs come with half the thickness of a Briggs gasket. That is step 1.
Step 2 is lap the intake manifold face and engine block areas. Every manifold I've seen is warped. Weight of carb and manifold hanging in the air with all the engine vibes over time. 220 wet/dry paper with soapy water on a sheet of plate glass. Go 400, 600 then 800 grits.
Make sure the fuel pump (spring and diaphragm) plunge into the body cleanly and evenly. I've had some Chinese ones that needed some metal massaging. Make sure it gets the full plunge travel as well.
This was a genuine B&S kit. It had the thick manifold gasket. Not sure I got the carb to manifold bolts as tight as they need to be. Hard to get a wrench on them. I'll give it another try.
Think that is an air screw. Should be 1-1.5 turns out. Check your engine manual to be sure. Going off a weak memory LOL.
Make sure the fuel pickup tube is not cracked. Also needs to be off the bottom of the tank a smidge.
Newer carbs do not have any adjustment screws. Older ones did.
Most likely you need to boil your carb clean. Cheap hot plate in the garage for an hour. Remove all plastic and rubber parts. Reem all jets/holes with fishing line. Don't use abrasive welding tip cleaners. You will open the jets up from factory sizes.
This was a genuine B&S kit. It had the thick manifold gasket. Not sure I got the carb to manifold bolts as tight as they need to be. Hard to get a wrench on them. I'll give it another try.
Air leaks at the carb gasket are often worse at idle than at high speed because of more vacuum at idle . When it's surging push the top of the carb side ways and if there is a gasket leak the engine may die . A least it would on my 1959 ford PU and also on a new 1964 that another guy was the proud owner of .
If the auxiliary tank, inside the main tank, does not fill properly you problem could be there. Only one way to find out, disassemble again. Engines this old have a tendency to rust out the auxiliary tank and you will no longer have the proper level of fuel there.
