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GV 2008 2520
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17 Posts
Discussion Starter #1
We have operated an early 90s (1990ish) 18hp Craftsman II with 44 inch deck successfully for about 12 years now on a ranch property and it has rarely given us any trouble. It is well maintained and last year while servicing and giving everything a thorough cleaning, I sprayed some carb cleaner down the air horn and it seemed to run a little stronger after.

However when I returned it to the ranch I noticed it started this quirky rolling surge of RPM, and I can see the governor arm moving in and out to compensate for the throttle position or something as it rolls up and down like a race engine. Does not do it under a load mowing at WOT, only while trying to idle or cruise around at lower throttle position. Fuel filter looks clean, but there is this little square box in line with the fuel line (not sure what that is), and I have never tried to remove the carb or rebuild it or anything.

Anyone else experience or recognize this symptom?

thanks
 

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Man w/skills
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996 Posts
Sounds to me like the engine is running lean. Spraying carb cleaner down the throat is not advisable, as it can do funky things in there if you have any rubber or other polymer parts inside the carb.

Time to remove the carb, disassemble, clean and probably put in a new carb kit (they are pretty cheap).

You may get away with just adjusting the carb, but IMHO unless you KNOW the carb is clean and the seals are good it's not much use to start playing with adjustments.
 

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716 Posts
Sounds to me like the engine is running lean. Spraying carb cleaner down the throat is not advisable, as it can do funky things in there if you have any rubber or other polymer parts inside the carb.

Time to remove the carb, disassemble, clean and probably put in a new carb kit (they are pretty cheap).

You may get away with just adjusting the carb, but IMHO unless you KNOW the carb is clean and the seals are good it's not much use to start playing with adjustments.
agreed, kits are fairly cheap, and it dosent take long to swap out the pieces :fing32:
 

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1,852 Posts
I would suggest the same as everyone else has. It is running lean on the lower throttle, that is why it is surging. I would take the carb off and soak it in carb cleaner for a day. you can buy the carb cleaner by the 1 gallon bucket, at Advanced Auto parts, Napa, Auto Zone, ......... it is not to expensive. I would also suggest getting a rebuild kit for the carb too. I would suggest a new fuel filter after I was done cleaning the carb.
I hope this helps you out, Good Luck:fing32:.
 

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GV 2008 2520
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17 Posts
Discussion Starter #5
Thanks for the reply posts and advise - I will probably just get one of those basket dip carb cleaner cans and do it the right way. Makes sense that it would lean out if it is leaking air, also I can make it go away with the choke knob so that is definitely it. I will look for a carb kit for that Briggs before I take it apart
thanks again
 

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Proud Wheel Horse Owner
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3,213 Posts
Don't do anything to the carb until you adjust the mixture screw. Make your adjustment after warming up the engine for a few minutes so that the heads and intake runners are hot. Adjust the mixture screw out (counter-clockwise) to achieve the best idle. Move it in small increments and wait between each movement, for the engine to stabilize. Then decide if you want to move it more. Once you achieve the best idle, move a bit further rich until the idle starts to just break and get rough again.........now you've found the spot that is just too rich. Come back lean from there (clockwise) just a tad, until you achieve that best idle again. That puts you on the slightly rich side, and makes for a very happy, and cool running engine.

In the future, use Seafoam in the fuel, as this will keep the carb clean on the inside, and absorb moisture, and help clean the carbon off the valves and combustion chambers. Store it out of the weather so that rain doesn't get down the vent in that upward facing fuel filler cap, and replace the cap with a new one, if it's damaged. Otherwise, it's a funnel for water and dirt.

Super nice machine. I've rescued quite a few and have one here right now if you need help comparing things.

Now.....if adjusting the mixture doesn't help, sure, take the carb apart and clean it.

BTW, shooting carb cleaner down the carb throat did not harm anything. The throat of the carb is metal, as is the intake manifold. The carb cleaner was there for all of a millisecond and down the hatch it went.
 

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GV 2008 2520
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17 Posts
Discussion Starter #7
Thanks for the reply - I love that seafoam stuff and use it on other engines and a chain saw - don't know why I didn't think to start storing the mover with that stuff as well. Have used Stabil and even a little Marvel Mystery Oil in the fuel now and then and this machine has never given me any trouble before.

Carb kit is sitting on my desk, if I got the correct one (Stens pn 520-080 replaces B&S 694056 Briggs), but I am game to try the mixture adjustment screw first as I will be doing this anyway if I rebuild the carb.

As per your comment about the machine in general: this is the single most capable and incredible riding lawn mower model I have ever seen. The tires are large enough to grab and climb over obstacles (I run them almost zero pressure on the pasture property). This thing will mow scotch broom, blackberry vines, weeds, grass, sapling trees whatever and never quits! The first season we bought this thing I thought I was going to destroy it beyond repair doing this kind of property mowing - That was 12 years ago! and it was a decade old when we got it! I have spare belts and have only ever needed them twice, uses a little oil now and that's it - my wife calls it the Tardis. I would recommend this lawn tractor to anyone.
 

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I have the smaller hp version of your tractor. Something like 11 or 12 hp or so, but it earns it's keep. I have done things with it that would kill or mangle other equipment. I have a larger 18 or 19hp MTD with hydro, but my little grey Craftsman II out pulls that MTD. And the Craftsman is not so cold blooded as the MTD either.
 
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