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Hi there,

I've started to notice my lawn mower start to surge when I'm using it. I cleaned out the carb a few months back and have a new air filter in it.

Any idea as to what might be the cause? Should I put in a new carb? I think maybe there is gunk in the fuel tank which impedes gas flow. I thought maybe when winter comes to let the gas burn off, then spray and wash the inside of the tank with water and then let it dry since it won't be used for a few months. Not sure if that would do the trick.

I've attached an image of my lawn mower. The model # is 917.385121.

Thanks!

A mower surging means you have a problem with the slow speed circuit in the carburetor. Cleaning or replacement of the carburetor your choice? After the repair clean fresh fuel and a new fuel filter.

Surging is usually caused by a lean mixture condition.

A lean condition can be caused by:

Out of adjustment low speed circuit (if carb is adjustable)

Partially clogged low speed circuit

Air (vacuum) leaks, such as intake gaskets or throttle shaft seals.


Some carburetors are so inexpensive that it's better to just replace them. Then run zero percent ethanol fuel.

Intek v 24's. One 13 yrs old, one 1 year old with 72 hours. Both surge occasionally . The old one has original carb never apart. Both use ethanol, but always treated with StaBil. Most recent surge started after weeks of short run times where oil temp never reached operating temp and then oil did reach 200F-bingo, surging. Then , after one day , it stopped. I cut open the gas filter and looked for anything , but nothing visible at 10 power.

Crud somehow sneaking through? Cutoff fuel solenoid (do I have one) balky? Who can tell. With the newer unit I have had two surges in one year that "cured" themselves. The last surge was very strong where I considered not running the tractor due to severe (almost) stops followed by pick up while running.

I follow the rule never to buy gas at a station while a big rig gas truck is replenishing the underground tanks. The urban legend is that the filling stirs up enough dirt to clog a fuel filter. True?

motoman said:

I follow the rule never to buy gas at a station while a big rig gas truck is replenishing the underground tanks. The urban legend is that the filling stirs up enough dirt to clog a fuel filter. True?

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It depends on how empty the tank is when the filling starts. If it's half full, not a problem. If it's empty or nearly so, it's going to stir up what's on the bottom. But the pumps have filters to catch dirt.

And, how do you know the truck didn't leave one minute before you got there?

We don't know what we don't know . Worry about that truck that just left will leave you out of gas in the boonies. Probabilities is all we can cling to. We could post a sentry with a cell phone.:laughing:

What makes me laugh is that most people think when you run a tank empty you get dirt from the bottom.
Truth is that all tanks pull from the bottom all the time. They also fill from the top. You can and do get whatever is on the bottom all the time. So keep those tanks clean.

Who controls the gas station tank filter change frequency? Up to the owner /operator? Major brands discipline better than others? Tractor/car filter catches all dirt til plugged? Cars stop running. Second most frequent tow- in problem after batteries is plugged fuel filters?

motoman said:

Who controls the gas station tank filter change frequency? Up to the owner /operator? Major brands discipline better than others? Tractor/car filter catches all dirt til plugged? Cars stop running. Second most frequent tow- in problem after batteries is plugged fuel filters?

Click to expand...

It kind of regulates itself. Fuel filters are not bypass-type filters; when they plug, gas quits flowing, customer complains, station replaces filter. The irony is that, the closer a fuel filter gets to plugging, the better job of filtering it does.

Most fuel filters have a useful life of a number of gallons they can be expected to filter, given normal conditions. Pumps keep track of the number of gallons they've pumped; it would not be hard to have an alarm notifying the owner that a filter change is due. My icemaker has one.

I hope topgun will forgive us a little off topic...This filtration thing is interesting. The hi flow foam filter company states that as their air filter becomes semi clogged it filters just as well or better. Then we have the filter medium diatomaceous earth (sp?) which is one of the best. And don't forget the sanitizing power of the good ole earth as it cleans the brown water from our septic systems. In only a few feet bacteria and viruses are eliminated. If the clogging factor is at work why do particles find their way into the carburetor orifices? Break offs? Tiniest? Non uniform clogging? No one really knows?

One of the most interesting air filters is the oil bath. It requires intake air to make a very sharp 180 degree turn. The particles of dirt, etc., suspended in the air, being heavier, can't make as tight of a turn. The dirt goes straight while the air turns. A nearby pool of oil awaits, and they are trapped.

I remember the "ancient" auto oil bath filter. A solid packed ring of dirt would form in the bottom of the filter housing. But we still do not know how some particles find their way into the carburetor passage ways....A bunch of particles small enough to pass through the filter and then coagulate into blockages? Or is it always "gumming" via chemical reaction of different materials such as platings, rubbers, plastics, gas additives? Or both, and what is in StaBil and other additives that minimizes problems?

Dirty air filter plugs in which makes for a richer fuel mixture, which in turns helps do away with the engine surging. The OP has a engine surge so I would think we are going into the wrong direction here looking at air filters. Its been a long time age ago when I can remember a oil bath oil filter on a lawn mower. I am thinking like the old gas powered reel mowers back in the 40's and early 50's ???

I'm no expert on this but lawnmowers and the like operate in dirty environments (compared to the average car) and they usually have vented, unfiltered gas caps. That's one possible source of dirt. The small gas engine fuel filters I've seen look to be very coarse. Not sure how much good they do.

Ethanol gas doesn't help, eitherr. It draws moisture which causes corrosion as well as adversely affecting rubber items not designed for it.

I quit using 87 octane years ago and that solved a lot of problems, I buy 10 gals of 91 at a time add 3oz of sea foam to each 5 gal. and I use this for all my 2cy to and my echo weed eater is 10 years old.