B & S Mower Engine - Fuel Not Feeding Engine + Primer Pumping Air

[UltramanNick]

I hope the experts here can help me out.

I have a YardMachine mower with a B&S engine (500). It was working fine two days ago, but suddenly stopped (i.e. no gas). I checked the gas, oil, everything looked fine. I pumped the primer and I didn't "feel" any liquid being pumped....all I heard was just "hsst, hsst." Hm. I decided to wait until the next day thinking I may have flooded it.

Still no start. Still, the primer just kept hissing. So I took off the air filter (which I had cleaned a few weeks ago), took off the fuel tank and dumped the old gas, cleaned the carb, checked the fuel lines....I'm no mechanic, but everything looked clear and good. I put it back together, got some fresh gas, put it in....and then pumped the primer. NOW I felt the liquid being pumped into the engine. The mower started.....ran irregularly for about 30 - 45 seconds, then died (i.e. out of gas). Tried the primer again, just air.

It appears that the engine ran with just the amount of gas inside the mower after it got primed and then died. So why isn't the gas still flowing into the engine?

So is gas just not getting to the engine somehow? The primer is only used to START it going, right? What else can I check without having to tear is apart even more? Any help would be much appreciated.

 

[greynold99]

UltramanNick,

First, I'm no expert and this is only my experience. Your mileage may vary...

If this B&S (500) engine is the same as the one on my 3 year old Weedeater 22" lawnmower, I think there was a defect in the mfg. process of the carburetor they put on this engine that restricted the fuel flow. 2 years ago, B&S actually sent me a replacement carb free of charge when I complained about a problem with the carb. And, when I received the replacement carb, there was a definite manufacturing change in the carb where what was plastic on the defective carb was replaced with a small stainless steel piece.
I've not had any problems since.

On the Do-it-Yourself forum around that same time, there was one poster who picked up a bunch of these Weedeater mowers in the Walmart trash dumpster when they threw them out. Some were new, many had been returned and he replaced the carb and then sold them for something less than the new price. I noticed shortly afterwards Walmart didn't carry the Weedeater brand of lawnmower anymore, at least not in my local area.

The design of these carbs hasn't changed much over the years and they always were reliable. In fact, before I got my replacement, I put a 15 yr old B&S carb on that I had on a broken mower as a test, and it worked fine.
Hope this helps,
greynold99

 

[Narko]

I had the same problems on my lawnmower. Took me a while to figure out the problems. The carb wasn't working because the O-ring to seal the carb to engine was old and flattened. Replaced the O-ring with a new and larger one (same inside dia.) and that solved the gas supply. As for the primer the gasket is critical as the air from the bulb (on mine anyway, b & s 12v802 , has to travel like 5/8 " to feed hole in carb. I made a new gasket out of mounting foam a little less than 1/8" thick which is sticky on both sides. After that the mower starts and runs fine.

 

[Rivets]

Narko, you do realize that this thread is 5 years old. I think the problem has been solved.

 

[Narko]

So that is why my brilliant diagnostics were not appreciated. LOL. No I did not realize the thread was so old. Yes, as a result of the prompt due to your comment I see there is a date relative to the posting. I am embarrassed. My implicit notion apparently was that if is up there, it is current. Thanks, I think. Narko

 

[ILENGINE]

So that is why my brilliant diagnostics were not appreciated. LOL. No I did not realize the thread was so old. Yes, as a result of the prompt due to your comment I see there is a date relative to the posting. I am embarrassed. My implicit notion apparently was that if is up there, it is current. Thanks, I think. Narko

the new guys seem to do it more than the people that have been here since day one.

 

[cpurvis]

Yes, it's a Lazarus thread but Narko's suggested fix was different than the previous fix by greynold99.

Isn't that a good thing in case someone else is looking to solve the same problem?