Surging engine - Briggs & Stratton / Sears
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    Evergreen's Avatar
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    Surging engine - Briggs & Stratton / Sears

    When I pulled the little Sears in my signature out of the barn this spring I noticed that the engine was revving itself up and down. Not enough to cause concern, but enough to notice it. Since then, the surging is getting more and more dramatic to the point that the machine is getting difficult to use. Here is the strange part though: it isn't a constant problem. I can go an acre without incident, spend several minutes fighting to keep it running, and then set off for another trouble-free acre of mowing. Load and engine temperature do not seem to have any effect on this problem one way or the other. In fact the only constant factor I can identify is that going over bumps or turning at high speed sometimes sets it off. I have sprayed the carb with cleaner and I've poured a quarter can of Seafoam into the gas tank, neither of these seem to have been effective. I'm convinced it is a carb issue because nothing else makes any sense... I just don't know what the issue is! Every other carburetor problem I've ever had was so much more consistent.

    I'd like a few opinions/suggestions/ideas before I order a carb kit. I don't like troubleshooting blindly.

    '50 Model M w/electronic ignition, 12v conversion, and a 3pt conversion plus a homemade snowplow, a Deere Model 51 trailer plow, a Woods RM59 finish mower, a Bark Buster splitter, and a few other toys.
    '69 Sears Suburban 14 48" deck and 42" back blade, an estate rake, and a sweeper.
    '07 F250 XL Powerstroke, crew cab, short box, 4x4.
    '85 F150... I finally sold my very first truck after racking up over half-a-million miles on the original drivetrain.

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    flyweight's Avatar
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    I have sprayed the carb with cleaner and I've poured a quarter can of Seafoam into the gas tank, neither of these seem to have been effective. I'm convinced it is a carb issue because nothing else makes any sense... I just don't know what the issue is! Every other carburetor problem I've ever had was so much more consistent.
    You're on track with a carb problem. Check the gasket(s), between the carb and engine block for a vacuum leak. Some of these small engine have a plastic, or phenolic spacer which can warp and suck air.
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    Michael

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    Evergreen's Avatar
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    That would make sense as sometimes it backfires during or immediately after one of these episodes. Sometimes it also has a hard time idling without small amounts of popping.

    If I find there is a problem with the gasket can I just use gasket-sheet and cut myself a new one or because it goes on the block, is there something special I need to use? I doubt I can get the parts easily as not a lot of stores stock parts for 45 year old machines up here.
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    '50 Model M w/electronic ignition, 12v conversion, and a 3pt conversion plus a homemade snowplow, a Deere Model 51 trailer plow, a Woods RM59 finish mower, a Bark Buster splitter, and a few other toys.
    '69 Sears Suburban 14 48" deck and 42" back blade, an estate rake, and a sweeper.
    '07 F250 XL Powerstroke, crew cab, short box, 4x4.
    '85 F150... I finally sold my very first truck after racking up over half-a-million miles on the original drivetrain.

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    Sometimes you just have to open the carburetor to clean it out. Solvents are good preventative maintenance when everything is working normally. If fuel evaporated in the float bowl you may have some deposits that need to be mechanically removed using a jet cleaning tool. You may have to remove and clean the emulsion tube as well. While you're at it make sure your governor linkage is clean and moving properly. Debris and corrosion can affect normal movement and cause surging especially when the carburetor needs to be serviced.
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    flyweight's Avatar
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    You can make your own gasket. Make sure you add the small vacuum hole(next to the main port, IF the original one had it).
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    Michael

    2019 JD Z540R 54" cutting deck w/MulchControl™
    1984 JD 750
    1971 JD 15 Chainsaw ← hasn't run since ~1975

    Also have a bunch of other stuff.
    ---------------------------------------

    " If there's no one around to smell me, do I really stink"? - John Wells - Brewster County, West Texas.









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    possible easy fix

    Check to see the bolts/screws holding the carb on are tight. My brother had a similar problem with a generator. A few turns with a screwdriver made it sing a constant note again. You'll get the same thing with a loose intake manifold. If that doesn't work, look at dumping the gas from the carb float bowl. You may have water/trash in it and as the mower bumps around it interferes.

    Hopefully it's something simple.

    Treefarmer
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    tj1
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    Could be a simple as SGS said, the governor.. If that is not working properly it will surge for sure.. Hope that's all it is for ya.
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    Jeff

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    Thanks a bunch everyone! I'm almost done with chores for the day and hopefully I'll be able to have a look at it before supper.

    I'll probably have to (*gasp*) wash the tractor before I begin messing with it.
    BigJim55 likes this.
    '50 Model M w/electronic ignition, 12v conversion, and a 3pt conversion plus a homemade snowplow, a Deere Model 51 trailer plow, a Woods RM59 finish mower, a Bark Buster splitter, and a few other toys.
    '69 Sears Suburban 14 48" deck and 42" back blade, an estate rake, and a sweeper.
    '07 F250 XL Powerstroke, crew cab, short box, 4x4.
    '85 F150... I finally sold my very first truck after racking up over half-a-million miles on the original drivetrain.

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    Evergreen's Avatar
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    Per the recommendations I got from you guys, I checked over the carb and found it to be solidly attached with intact gaskets. I did get some gunk out of the bottom of the bowl that looked like varnished gas flakes, but otherwise the carb and float looked good. In my race to get my hay in, I haven't really messed with it beyond that.

    Well today I used the old Sears to help shuffle some stuff around in the barn and was surprised to find that the surging was gone. I was greeted with a cloud of white smoke when I started it up, but that cleared quickly. I wonder if sitting full of that heavy dose of sea foam was enough to clear it out? I'll probably have to mow at the end of the week so I'll know for sure then.
    '50 Model M w/electronic ignition, 12v conversion, and a 3pt conversion plus a homemade snowplow, a Deere Model 51 trailer plow, a Woods RM59 finish mower, a Bark Buster splitter, and a few other toys.
    '69 Sears Suburban 14 48" deck and 42" back blade, an estate rake, and a sweeper.
    '07 F250 XL Powerstroke, crew cab, short box, 4x4.
    '85 F150... I finally sold my very first truck after racking up over half-a-million miles on the original drivetrain.

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    Evergreen's Avatar
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    So, the surging came back a few days after I posted my last message, but I was in the process of moving and didn't look into the problem as there were other things to be taken care of. Now that we are almost unpacked, I have had some time to look into the problem and I think I finally found the cause... The engine was so dirty that the linkage from the carb to the govenor was basically stuck. A quick blast with the power washer and some scraping with a wire brush and it works now! The funny thing is that now my wire brush smells like horse crap... it is funny because the tractor hasn't been around horse crap since the late 1980's.
    '50 Model M w/electronic ignition, 12v conversion, and a 3pt conversion plus a homemade snowplow, a Deere Model 51 trailer plow, a Woods RM59 finish mower, a Bark Buster splitter, and a few other toys.
    '69 Sears Suburban 14 48" deck and 42" back blade, an estate rake, and a sweeper.
    '07 F250 XL Powerstroke, crew cab, short box, 4x4.
    '85 F150... I finally sold my very first truck after racking up over half-a-million miles on the original drivetrain.

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