Hi gang. F-I-L brought me his TroyBilt rider with the Briggs&Stratton 17HP (9BSXS.5002VP) engine. It was running, but VERY rich; missing and black smoke, like the choke was stuck on. It has the crappy Nikki carb with the white plastic "metering plate" with the main jet pressed into it. NOT my favorite carb, but it is as simple as they come.
The choke shaft was gummy - had a foam gasket on the top shaft that had disintegrated. And there was some crud in the brass vent orifice beside the choke plate. Tore the carb down and cleaned everything thoroughly and blew through all passages with carb cleaner and then compressed air. All internal carb parts look good. I gave the inlet needle and seat particular attention (10x lighted magnification). Freed up the choke shaft and lubed it and main throttle butterfly so they both move freely. Cut off the EPA/lawyer stops on the idle jet, removed it and cleaned the needle and passages. Set to 1-1/2 turns out. Cleaned the bowl/fuel shutoff solenoid and tested it - works perfect. After assembling the float/inlet needle/pivot, I "blow" tested it (mouth pressure) to verify that the needle cuts off flow as the float is raised (float level is NOT adjustable AFAIK). Examined the existing bowl/plate gasket with magnification - all looks good.
It restarted easy and runs good, but at what seems to be nearly wide open throttle. No smoke, no missing, sounds strong. I checked the governor and throttle linkage while it was running - it all moves freely and the governor and throttle linkage has the main throttle butterfly CLOSED all the way to the idle stop!! So I'm somehow getting excess fuel and air, but I cannot fathom where from. The choke is now fully open as it should be (closes only when manual throttle is in choke position). Intake manifold is tight and there are no visible cracks or other leaks. The main throttle shaft is a tiny bit worn, but I doubt it is leaking enough to cause this. Closing the idle jet all the way makes only a slight difference.
What am I missing???
The choke shaft was gummy - had a foam gasket on the top shaft that had disintegrated. And there was some crud in the brass vent orifice beside the choke plate. Tore the carb down and cleaned everything thoroughly and blew through all passages with carb cleaner and then compressed air. All internal carb parts look good. I gave the inlet needle and seat particular attention (10x lighted magnification). Freed up the choke shaft and lubed it and main throttle butterfly so they both move freely. Cut off the EPA/lawyer stops on the idle jet, removed it and cleaned the needle and passages. Set to 1-1/2 turns out. Cleaned the bowl/fuel shutoff solenoid and tested it - works perfect. After assembling the float/inlet needle/pivot, I "blow" tested it (mouth pressure) to verify that the needle cuts off flow as the float is raised (float level is NOT adjustable AFAIK). Examined the existing bowl/plate gasket with magnification - all looks good.
It restarted easy and runs good, but at what seems to be nearly wide open throttle. No smoke, no missing, sounds strong. I checked the governor and throttle linkage while it was running - it all moves freely and the governor and throttle linkage has the main throttle butterfly CLOSED all the way to the idle stop!! So I'm somehow getting excess fuel and air, but I cannot fathom where from. The choke is now fully open as it should be (closes only when manual throttle is in choke position). Intake manifold is tight and there are no visible cracks or other leaks. The main throttle shaft is a tiny bit worn, but I doubt it is leaking enough to cause this. Closing the idle jet all the way makes only a slight difference.
What am I missing???
