Briggs/ Walbro idle tuning

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35,776
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ME
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Found a generator at the town dump with a 10hp briggs 19g412 engine. Cleaned out its carb, ran well on half choke, surged otherwise. Could have dug deeper into cleaning the emulsion tubes but for $15 I just got this replacement carby for it. It now runs well on no choke, but starts hard. Needs a whiff of ether to get going. My "perfectly good" 3-month old gas has a summer RVP, may be an issue, am pursuing fresh fuel. But it runs in all my other OPE. Notably this thing's choke plate only closes to 45 degrees and is full of holes. Anyway this unit has a knurled, nearly head-less hard-to-turn screw (with an anti-vibration spring) that seems to be for the idle mix. My question is, is turning this out/ CCW something that enriches the mix or leans it out (with more air)? It came screwed all the way down. And does it even matter? At rest, when starting, the governor has the throttle wide open, so the idle circuit contribution would be minimal. There are little holes in the vicinity of the throttle plate, which, when it's closed, sensibly lead to the area of this screw. One would think this is google-able, but the best info I can find is, yeah, guy, mess with this until it runs well. mad
 
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2,700
Location
USA
Remove all electrical load, pull on the throttle plate against the governor spring so the throttle plate nearly closed (there should be a screw to stop it before closing fully) and adjust the idle mix screw for the most rpm. This should be a conventional needle valve where opening it (counterclockwise) makes it richer and turning clockwise closes off the fuel making it leaner. Then turn the screw out a little so it has good response when you let go of the plate and it quickly runs up to governed rpm. If the idle circuit isn't working it will tend to surge with no load-- because when the governor closes the throttle it either starves or floods and dies completely-- but smooth out when loaded.
 
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Messages
4,605
Location
The Garden State
If it runs good once you get it going then it sounds like your choke or it's linkage may not be set correctly. I have a similar B&S engine in my B&S generator and if I "forget" to choke it it'll take lots of pulls to try to start it. If I set the choke lever before I pull the starter it'll start on the second pull without fail. If my gasoline wasn't so old it would probably start on the first pull grin2. My gen was bought new in 2012 and I've never had to change or clean the carb so I've not touched the choke linkage. Whimsey
 
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35,776
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ME
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Choke is spring loaded at the carb. I was able to bend the plate slightly with a pair of pliers and now it closes better, and starts without ether when luke-warm on fresh fuel. However, it still runs best on half-choke. I've ordered a small drill bit set so I can hog out the main jet. Wish me luck!
 
Messages
35,776
Location
ME
Thread starter
So I got my drill bits and went at it. The 1.03mm bit slipped through like a hotdog down a hallway. The 1.17mm one didn't, so I worked it through. Genny started on the first pull with choke, warmed up in ~10 seconds, and runs perfectly under load (1500 watt space heater.) Surges slightly without load. Tried messing with the idle jet, didn't get anywhere. Nevermind, I wouldn't run it without load. Case closed, I guess.
 
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