# Briggs 3.5 on McLane edger won't stay running



## White94RX (Jan 23, 2021)

I'm hoping you guys can help me before I throw this thing in the scrap metal bin. I've got a McLane edger, with a B&S 3.5 on it. I think it is a 091202 or similar. Backstory is that like always, it sat unused for anywhere between 5-8 years. So I took the carb off, cleaned it out, and reassembled. It ran, but wouldn't stay running without some choke. I could play with the choke back and forth, and it would stay running. But if you turned it all the way off, it would die within a few seconds. Obviously I think it's fuel related, and the gasket between the gas tank and carb was barely existent, and I figured it was sucking air. In my search for a gasket set, of course I found a totally new carb, with gaskets for $20 on Amazon. Done. So I installed it, and it went well enough. Started right up and ran flawlessly for about 10 minutes or so. Throttle worked, choke worked, etc. Good to go, or so I thought.

I brought it home, and a few days or a week later, I went to run it again. It took about 15-20 pulls before it finally fired up, but when it did, it ran totally normally. Another week or so goes by and now I'm thinking about using it (itching to do some yard work, this cold weather is killing me). Now it starts right away, but does the same thing it originally did. Won't stay running without playing with the choke. So I'm thinking this chinese carb is junk, so I put the original back on, with the new gaskets from the new carb. Same issue. Won't stay running without working the choke. I really don't know anything about how these governors and springs work, but playing with the throttle plate doesn't seem to change much aside from revving the engine super high. I tried bending the linkage up or down (effectively shortening or straightening it) with no change.

I'm thinking it has to be fuel/air related, right? I get my can of brake clean, and spray around with it running, and it's definitely seems to be affecting it. Aside from the gasket where the carb mounts on the tank, and carb to the engine, what else is there? And both new and original carbs behave the same way. Hoping someone can shed some light on this for me and get this thing running. I'm considering swapping it for a predator engine, but don't really want to put any money into it. It came free from my mother, and I've only spent $20 on it so far. Thanks!


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## SNOWBOB11 (Aug 31, 2017)

Does that motor have a primer bulb? Any chance it's cracked? Also have you changed the spark plug just in case? The Chinese carbs are actually pretty good for most small engines.

Try something and see if it helps. Remove the gas cap and run it without it and see if it helps. The gas cap needs to breath and if the breather has fallen off or crumbled it could be affecting it.


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## White94RX (Jan 23, 2021)

No primer bulb. I did change the plug just to rule it out. I'll try taking off the gas cap and see what happens. Is there anything beyond the carb, but before the combustion chamber that could crack or leak? Basically what would be considered the intake manifold? Aside from removing and replacing carbs, I haven't done much to these engines. Thanks for your response.


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## MasterMech (Sep 24, 2017)

Most common failure on the old vacujet or pulsajet Briggs stuff was the diaphragm between the tank and the carb. In your case, this diaphragm is built into the side of the carb. Another common problem was the pickup tubes vibrating loose from the carb bodies. Since it's behaving similarly with both carbs, and all of the intake tract is built into the carb body, the problem may not even be with the engine itself, assuming it makes healthy compression.

Have you cleaned and flushed the fuel tank? Small amounts of water in the fuel build up in the carb while the engine is running. When you changed the carb, the carb probably picked up clean fuel until engine vibration emulsifies water from the tank bottom into the fuel. These droplets then get sucked into the carb where they accumulate in the bowl or diaphragm chamber. Once you get enough water, the engine will start to act up again.


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## MasterMech (Sep 24, 2017)

Most common failure on the old vacujet or pulsajet Briggs stuff was the diaphragm between the tank and the carb. In your case, this diaphragm is built into the side of the carb. Another common problem was the pickup tubes vibrating loose from the carb bodies. Since it's behaving similarly with both carbs, and all of the intake tract is built into the carb body, the problem may not even be with the engine itself, assuming it makes healthy compression.

Have you cleaned and flushed the fuel tank? Small amounts of water in the fuel build up in the carb while the engine is running. When you changed the carb, the carb probably picked up clean fuel until engine vibration emulsifies water from the tank bottom into the fuel. These droplets then get sucked into the carb where they accumulate in the bowl or diaphragm chamber. Once you get enough water, the engine will start to act up again.


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## White94RX (Jan 23, 2021)

Yeah, I've dumped and cleaned the tank twice now. I'm about to dump it for a predator engine. I'm assuming one of those will bolt right up?

But thank you for confirming that there's nothing past the carb itself.


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## MasterMech (Sep 24, 2017)

The other avenue could be low compression. This isn't easy to test on a small engine (due to built in compression release for starting), and a cylinder leakage tester will cost you more than a replacement engine. If you're handy, you can rig a fitting Appalachian-style in the spark plug hole with the piston fixed somewhere on the compression/power stroke. Put some compressed air to it and if you can hear leakage from the oil fill port (I recommend doing this with an empty crankcase....), head gasket, carburetor, or muffler, then you'll have a fair idea of where you are losing compression. Some leakage past the rings into the crankcase is acceptable, too much is, well, too much.


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## White94RX (Jan 23, 2021)

Final update: got it running properly.

I think the tank wasn't as clean as I thought it was, and the new carb I put on got something in it. Yesterday, I put the new carb back on. But before I did, I blew out all the passages and jets with compressed air. I had noticed the fuel pump spring cap didn't quite fit the bore properly and would get stuck, so I used the spring cap from the original carb as a precaution. It definitely fit better. Anyway, runs normally for now! Thanks for the help.


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