# Refurbishing an old lawn tractor, 18hp briggs idle hunts



## bobotech (Oct 6, 2006)

I have an old Lawn Chief from around 1987 that I'm finally getting around to fixing back up.

I only kept it because it has all the accessories for it, the underframe snow blower attachment, the bagging assembly, and the mower deck. Otherwise I probably would have let it go long ago.

Anyway, it originally had a 12HP briggs engine in it that threw a rod or something broke internally. It was a goner. Happened about 6 or 7 years ago.

So a couple years ago I bought a 18HP briggs twin to replace that engine. Then I promptly abandoned the project and got involved with other things.

Fast forward to this week. My buddy and i are trying to get it running again. We have gotten it running but we had to tear down the carb and do a bunch of clean up on it, had ports plugged and all sorts of stuff. ]

Turns out that one of the fuel lines was badly clogged causing a lot of grief as well.

My main question is will a restricted fuel line cause the engine to hunt? The engine revs will go up and down. What causes behavior like that to occur? 

Other than the hunting of the rpms, the engine runs well.


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## justin3 (Apr 10, 2007)

Generally engine hunting is normally caused by a restriction in the carburetor. Your best bet is to soak the carb in a cleaner and purchase a rebuild kit. Also make sure the intake manifold bolts are tight.


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## paulr44 (Oct 14, 2008)

Some may disagree with me on this, but from experience I'd have to say that the old B&S twin I/C engines were very hard to eliminate cycling, or "hunting" on. You should be able to eliminate most, if not all by cleaning the carb. spotlessly, and it must have no wear in the throttle shaft area. Adjust governor free play (AKA static adjustment), ensure there's no intake vacuum leaks, and that the fuel is fresh.

No, a restricted fuel line won't be the cause of the hunting, if, as you say it runs okay at full throttle under load. Restricted lines would usually cause a slowing-down, or an inability to achieve full RPM, or a power loss under load.


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## bobotech (Oct 6, 2006)

My engine wasn't running well after a short bit of time. It would run well for a short bit and then start to starve for fuel and you would have to close the choke to keep it running. It would then die and nothing you could do would keep it running. Well it turned out that the fuel line was almost totally plugged except for a pinhole sized passage. 

We took the top off the carb and cranked the engine to see how much fuel was pumping and there was nearly none coming out of the fuel supply hole on the top of the carb. It was barely dribbling out. This was before we replaced the fuel line.

So my buddy replaced the fuel line while I was at work. When he cranked the engine over, fuel started shooting out of that hole like it was a fountain, much much more than before.

Put the tractor back together and it runs nearly perfect. We don't have to choke the hell out of it to keep it running anymore and the surging/hunting is MUCH less, not perfect but much better.

I am going to buy a carb rebuild kit anyway and probably get a spare carb and rebuild it at my leisure and make it spotless and hopefully that will make the engine run nearly perfect.

At this point, the engine is running well enough to be perfectly serviceable. It still surges once in a while but NOTHING like it was.


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## golftech (Jan 3, 2009)

This "briggs twin" you're talking about, is it a Vanguard?? If it only does it while idling,forget it!! They all do it. I have 5.


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## bobotech (Oct 6, 2006)

No, this isn't a Vanguard, this is an older 180 opposed twin, not the v-twin.


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## dj722000 (Oct 29, 2008)

I agree with paulr44, drop the carb, tear it down, soak it, clean it, rebuild it. For 20 - 25 bucks, less headaches. Put it back in. I think from doing this you should be good to go. Guaranteed, with a plugged fuel line, you have gunk in the carb thats blocking passages that it needs to run smooth. (When soaking, take plastic or rubber parts off it!!!)


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## paulr44 (Oct 14, 2008)

The fuel line clog indicates the line should be replaced - if you haven't, then you'll probably be cleaning the carb. out again.
Lines degrade over time and the small particles easily bypass filters.


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## Lawnmowertech (Nov 12, 2008)

paulr44 said:


> The fuel line clog indicates the line should be replaced - if you haven't, then you'll probably be cleaning the carb. out again.
> Lines degrade over time and the small particles easily bypass filters.


paul did you know about the oregon yellow tygon type fuel line that hooks onto them briggs engines that you can see thru and the good thing is it dont need a clamp


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## paulr44 (Oct 14, 2008)

Lawnmowertech said:


> paul did you know about the oregon yellow tygon type fuel line that hooks onto them briggs engines that you can see thru and the good thing is it dont need a clamp


Yes, thank you. I found that the "aftermarket" line hardens up rather quickly, so a few years ago I switched to using only Tygon (from Stens) lines for 2-stroke, which stays pliable longer.
We don't use Tygon for most 4-strokes as our customer base is a little rough and we need thicker line with abrasion/puncture resistance (B&S or Tec. 1/4"), and use Tecumseh 26460 line clamps.


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