B&S Vanguard Choking Out

[m38inmaine]

HI all, have a 1993 briggs vanguard 12.5hp v-twin engine in my MaxII. When the air cleaner is on it chokes the engine out, blows black smoke and has no power and idles very rough. Take the air cleaner assy off and she runs/idles great. Installed a new crankcase vent and installed a new K&N air filter with no change, also 160lbs compression on both sides. Adjusted the float per the manual as well as adjusted the low speed per manual no change. Any ideas appreciated.

[jpswift1]

I don't know if it's possible or not, but could the choke lever or choke cable hold down be loose? Could the air cleaner be pushing down on the choke lever or butterfly when you put it on? It sounds like your Max is a early 1990's model when they first started using the Vanguards (12.5/14/16HP). These early Vanguards had the square plastic air cleaner housing. I have an early 90's Max II and it has the 16HP and mine was doing the same thing. That's how I fixed it......it was a simple, easy fix, but it was driving me nuts when I was trying to pinpoint the issue.

[rentalrider]

I've never seen the 12hp variety but just thinking aloud here is it possible the "bottom" of the aircleaner assembly is pushing on the butterfly? As in closing it? I'd leave running and try installing the air cleaner assembly and see when exactly this change takes place.

edit: jpswift beat me to it lol

[m38inmaine]

I'll check the housing issue, although it is a metal housing. I do know the choke cable/mount is tight and secure. Thanks.

[amphibious drew]

I would check the push rods.

[m38inmaine]

The Max is back up and running. Since the rebuild the engine performance has been hit or miss. So I decided to take the carb off and give it a good look over and clean. Looking inside it looked ok, apart I found some black piece lodged in the high speed jet partially blocking the orifice. A buddy offered to run it through his ultrasonic cleaner. Amazing what ended up at the bottom of the tray, stuff oozed out from every nook and cranny. Re assembled, also adjusted the valves and changed the plugs while I was in there. Now she runs like a new machine. Thanks for all the help and advice.