Proper Idle Mixture Screw & engine RPM settings? - Briggs 23 Hp Vanguard

[Gordon308]

Horizontal shaft, 23.0 Hp Vanguard engine, model 386447-3079-G1, equipped with (according to the Service Manual) a Nikki carburetor.

1. What is the proper initial setting of the Idle Mixture Screw? My service manual says the initial settings on the Idle Mixture Screws should be 3/4 of a turn COUNTERclockwise (CCW) from a "lightly seated" position (fully closed). HOWEVER, if you read the (somewhat generic) information on the Vanguard website regarding carburetor adjustments, it says the initial position of the Idle Mixture Screw should be 1-1/2 turns CCW - That's a 2X difference. I'm assuming the Service Manual is correct and the website doesn't address every Vanguard engine & carburetor available, but if anyone has any special guidance here, I would appreciate it. BTW - the engine starts & runs on either Idle Mixture Screw setting, but it does smell a little rich at the 1.5 turns CCW setting.

2. Is the Governed Idle Spring supposed to be disconnected when I do the final Idle Mixture Screw adjustments? The Service Manual says for the FINAL Idle Mixture adjustment, it should be performed with the engine running at 1200 RPM. I am unable to get my engine to idle smoothly at that slow of speed. It surges between 1200 -1500 RPM, but never runs smoothly and repeatedly dies. If I hold the Throttle Lever against the Idle Speed Screw as the Manual states, it most definitely will die. The next section in the Manual says after the Idle Mixture is finalized, the governed Idle Tang should be adjusted so the engine operates at 1750 RPM (I have the red Governed Idle Spring), so is the Governed Idle Spring supposed to be disconnected when I set the engine RPM to 1200 and do the final Idle Mixture Screw adjustments?

 

[ILENGINE]

The confusion is some models use 3/4 turn out and some use 1 1/2 turns out. Carb adjustment is done while holding the throttle plate closed against the throttle speed adjustment screw on the carb, so the spring doesn't need to be unhooked. Setting speed is suppose to be 1200 but on occasion an engine won't go that low. Maybe try to get close while adjusting the screws. According to the manual turn the screw in until the engines starts to slow than back off 3/8 turn and recheck idle speed and adjust if needed then do the same to the number two cylinder.

final adjustment could be in the range of about 1 turn give or take. For the most part I would say if the engine is running fine at 3/4 turn adjustment and accelerated smoothly I wouldn't worry about it.

 

[Gordon308]

Setting speed is suppose to be 1200 but on occasion an engine won't go that low.

The reason this engine is unable to idle at a lower speed is starting to be a clearer picture now. In this John Deere 318 Lawn Tractor, the shaft powering the hydro-static transmission and other hydraulics is bolted directly to the flywheel and there is no disconnect or clutch. Even with no ground movement of the tractor that pump is always putting some amount of load on the engine in case it needs to raise/lower accessory equipment or turn the power steering.