Lawnmower starting

Sun Jul 03, 2011 4:22 pm

I have an old Yard Machines lawnmower that I use to cut brush and rough areas.

This year, I put in fresh gas and Seafoam, pushed the primer button three times and it started and ran for a few seconds; then quit.

I realized that it will only run as long as I am pressing the primer button rapidly over and over. If I stop pushing the button, the engine dies.

What could be the cause of this? How do I fix it?


I asked my son what they taught him in his small engine class. He said since they weren't allowed to put gas in anything, he didn't learn much.

Re: Lawnmower starting

Sun Jul 03, 2011 4:43 pm

John C wrote:I asked my son what they taught him in his small engine class. He said since they weren't allowed to put gas in anything, he didn't learn much.

Doesn't sound like much of a school if he didn't learn much.

If you have a rubber fuel line check it good for cracks. My log splitter gave me the same problem until I found a crack in the line. It was in a spot you wouldn't see easily. I replaced it and she ran fin.

Re: Lawnmower starting

Sun Jul 03, 2011 5:42 pm

Barnyard wrote:
John C wrote:I asked my son what they taught him in his small engine class. He said since they weren't allowed to put gas in anything, he didn't learn much.

Doesn't sound like much of a school if he didn't learn much.

If you have a rubber fuel line check it good for cracks. My log splitter gave me the same problem until I found a crack in the line. It was in a spot you wouldn't see easily. I replaced it and she ran fin.


Bill, I went to a great school and learned very little.

So the fuel line could be cracked from age. Wouldn't it be leaking fuel?

Or could the crack be drawing air in....?

Funny you should mention the logsplitter. We have that and a Troy Bilt Horse tiller that have both not run in 15+ years. They are on the project list; along with Dad's 1975 C60 truck with 10K original miles. He was just too busy with work to keep everything running.

Re: Lawnmower starting

Sun Jul 03, 2011 5:45 pm

Mine didn't leak but I guess it was just drawing air.

Re: Lawnmower starting

Sun Jul 03, 2011 5:48 pm

I have had a similar problem and solution (cracked fuel line/replace the line) on a lawnmower. That is where I would start.

~ Jim

Re: Lawnmower starting

Mon Jul 04, 2011 12:41 pm

the engines with primer bulbs are called pulse jets,and depend on the lines not leaking to suck fuel up into the carb. If it has the little cream or yellowish colored fuel lines on it, they are bad for the ethanol in modern fuel to deteriorate them. Unfortunately, much of the time the fuel tank has to also be replaced to keep them from leaking.

Re: Lawnmower starting

Mon Jul 04, 2011 7:28 pm

Several engine manufacturers use the priming bulb. My thought - carburetor is gummed up.

Put about 1/3 bottle of carburetor - fuel system cleaner in with a full tank of gas. Slosh the mixture around. Then lay the lawn mower over with the carburetor side down for a minute or two - right or left side - idea is to soak the carburetor from the fuel inlet side with the solvent fuel mixture. Set mower upright. Wait for any dripped fuel to evaporate. Then start the engine using the priming bulb. When engine sputters - push the bulb again. It may take a few minutes for the engine to operate by it self.

If this doesn't work - then disassemble and locate the problem.

Re: Lawnmower starting

Mon Jul 04, 2011 9:13 pm

Both theories are good. My wife bought the mower in 1995 against my better judgement. Don't remember exactly why, but I seem to remember there were some words said at the time.

Anyway, it has been a pretty decent mower except for the time the pull rope broke and it took me 8 years to get around to replacing it. I just replaced the fuel line on my riding mower and was thinking this one could stand replacing as well.

I didn't want to drive to town today to pick up the fuel line, so I was delighted to find the old rubber line off my Cub while cleaning up this evening. Thanks to Russ Leggitt making me a beautiful steel line for the Cub, I now have an extra piece of hose to use on the lawn mower.

If replacing the hose doesn't help, I'll put some ether in the tank and see if it will clear out the carb.

Thanks!!

Re: Lawnmower starting

Tue Jul 05, 2011 11:33 am

I don't believe Briggs was still making the pulsa jet carbs in 1995 but if they were the fuel pump diaphram may be bad. If the fuel tank is large and mounted to the bottom of the carb then it may be an old pulsajet that has the fuel pump diaphram under a 4 screw cover on the left side of the carb. Likely it is just a float carb with a primer bulb. Clean the carb as Eugene said or I just remove the carb and clean with spray carb cleaner. If it has a float type carb then there is really no vacuum and should not suck air even with a cracked fuel line. Since the primer bulb is working, your symptoms describe a dirty carb.
Don't put ether in the tank.

Re: Lawnmower starting

Tue Jul 05, 2011 3:24 pm

1995 purchased. Sitting for 8 years???. Guessing again, one or both valves in the fuel pump diaphragm are stuck as Landreo described.

8 different B&S diaphragms shown in the parts catalog. Available at most auto parts store. You will need the information on the engine data plate to get the correct one.

Actually, try my suggestion first. If that doesn't work, carefully remove the fuel pump cover. Perhaps you can unstick the valves without tearing up the diaphragm.

Re: Lawnmower starting

Sat Jul 09, 2011 9:06 pm

Well, replacing the fuel line didn't work.

I'll see if I can figure out how to get the carb off and get it clean. Doesn't look easy though.

Dad thinks the float might be stuck.

I do have a can of carb cleaner I could spray in the tank and see if that will work its way into the carb.....

Re: Lawnmower starting

Sat Jul 09, 2011 10:15 pm

If this is really a pulsa jet then there aint no float, if your having to push the primer to keep it running then its the fuel pump diaphram, as its not pumping fuel up to the first stage. There is a small chance that its one of the other things mentioned here, but 99 % of the time its the pump. You can get the whole kit for about $6 at most small engine stores. Takes about half an hour to pull it off and redo the gaskets and spring inside.

Re: Lawnmower starting

Mon Jul 11, 2011 8:59 am

SInce there is a fuel line it is NOT a pulsajet carb. Try Eugene's technique or just remove the carb. The primer bulb should pressurize the float chamber, since the primer system works, the float is not stuck. If Eugene's technique does not work just pull the carb and spray cleaner/air into the mainjet/discharge nozzle. If the carb is a Briggs then you are done. Some Tecumseh carbs have a hidden ball check valve that is not accessable. If it is a Tecumseh engine, clean and then hold the carb throttle and choke so they do not rattle and shake the carb. If you hear a rattle then that check valve is free. Taking off, cleaning, reassemble should be 30 minutes.