B&S 675 Series 190cc - Fast idle to stall

[mysguidednlv]

I've been battling an idle issue with a B&S 675 Series 190cc engine... its the model with the "auto-choke" (which is a royal pain:thumbdown. When I start the mower, it usually starts within 5 pulls, the engine revs up to well over the 3300 which is the standard idle speed (my best guess would be somewhere in the low to mid 4k range). The engine temp jumps up pretty quickly activating the auto-choke "knob" which in turn closes the throttle plate. Within 10 seconds of this, the RPMs gradually drop down to the point where it stalls. I've tried adjusting the governor plate and can't seem to find a point where it will stay idling.

Before it started doing this, it would simply run at high idle continuously (roughly high 3ks), then yesterday, this started happening.

I've pulled and cleaned the carb, checked the plug (it's good), tried adjusting the governor plate, checked and confirmed the auto-choke is working... any other suggestions on what may be causing this issue? My next thought is to replace the governor and throttle-plate arm springs, but the mower has only been used for ~3 years and seems too new for springs to be a problem. Any other ideas are greatly appreciated!

 

[Rivets]

First of all you are not going to like my answer, but I must to help other members and guests. You don't know what you are working on or talking about. First, the auto choke air vane is connected to the throttle, it is also attached to the choke. Second, the governor air vane is attached to the throttle. Third, the auto choke air vane and the governor air vane are one and the same. Fourth, I have no idea what a governor "plate" and auto choke "knob" are. Fifth, there is a thermistor, some call it wax in a can, attached to the muffler which has a lever which forces the choke fully open as the engine warms up. The two springs, which you talk about are, small roughly 1/8" in DIA, is the auto choke return spring, which closes the choke as the engine cools down. The larger roughly 1/4" in DIA, is the engine speed control spring, which works with the air vane to set running RPM's. In normal operation at start-up your engine will rev to close to 4000 RPM's due to the rich mixture. As the engine warms up the choke will open (creating a leaner mixture) and engine speed will decrease. This normally will take three to five seconds. I will normally set operating RPM's on these engines at about 3,200 RPM's. There is no idle on these engine, full speed or off. If you have been playing around with this system, without knowing how it works, I would have a service tech replace those springs and adjust both the auto choke and carb speed. To all who read this thread, this system works extremely well when adjusted properly. I'm told there are some u-tube videos which do a better job of explaining the system and how to adjust, without blowing a rod through the block. To the OP, what you are trying to do, is going to get someone hurt. You can start hating me now.