I have a simplicity mower (1998) with a 16hp vertical shaft vanguard v-twin engine (303777 1111-51). Yesterday, after running the mower with turbo bagger attachment (a little extra load on the engine), for about 20 minutes, I idled back the engine and it began belching large clouds of blue/white smoke. The engine appeared warmer than normal. Plenty of heat and vapors when I removed the oil dipstick to check the oil level. The oil level was at the lower edge of the "OK" level. I let the engine cool and changed the oil. (It was about time, 23 hours of use). I restarted the engine and it appeared fine. Smooth idle, normal power, etc. I finished the lawn w/o the bagger but can still make it blow some smoke when the engine is hot, if I quickly move the throttle from wide open to idle. Will not blow smoke if the transition from wide open to idle is made slowly. The engine has approx 270 hours of use with regular oil changes.
Any thoughts..?

It sounds like a blown head gasket... ohv correct? Being it's a v twin, does it have duel exhaust? What I mean by that, each cylinder has its own exhaust pipe? If it does which side is it smoking?

Ouch, a head gasket! You are correct, it is an OHV, vert shaft, V-twin. Each cylinder has its own exhaust port, however the exhaust pipe from each cylinder feed into a single muffler. Therefore cannot tell which is doing the smoking. Would I be able to determine which cylinder is causing the problem with a compression check?

Nope... can't tell with a compression test... this is why I was hoping it had duel exhaust, so to tell which cylinder it was.. if it was just one.

I appreciate the help so far, thanks. I've ordered a B&S V-twin OHV Vanguard repair manual. It sounds like I will need to inspect both head gaskets.
Once I get this far into the motor, would you recommend replacing any other components as well?
Is this a reasonable repair for someone with decent mechanical ability?

Keep in mind, it's still running well. Mowed last night, but still a little smoke when bringing the throttle back to idle. Hoping to make it another month, it's leaf chopping season.

No, not much else to be done, maybe clean it all up while your there, you'll have to adjust the valves also...

Got my service manual today. Head gasket replacement and valve adjust looks fairly straightforward. I'm still hoping to get through "leaf chopping" season with the engine, prior to starting the repair. I suspect that the engine will let me know (lot of smoke), when its time for the repair.

Briggsdude, thanks again for the advice.

No problem... just be sure to check the oil a lot!!

Is the fuel tank mounted above the engine? Sometimes the fuel will enter the crankcase and overfill with a diluted oil causing it to burn the excess and cause a lot of smoke.. . also will do it on high idle do to crankcase turbulance.

Yes fuel can enter the crankcase by a bad float, or leaky inlet needle and or seat.. but when he changed the oil and it did the same thing, that pretty much ruled it out. Never seen one blow blue/white smoke on high idle unless of course the rings were very well shot. Usually on these ohv engines, it'll be fine one minute and then start puffing oil the next.. blows the gasket in the thin spot... over pressurizes the crankcase which in turn makes it burn oil when you rev it up and down, or when it gets heated up more and the oil thins more.

It's the "blue White" that is usually a combo of fuel oil. I guess I missed the oil change did the same thing BUT how long after the change did it do it again? Given the history of that engine I am still suspect. Will be interested in finding out.

I have a 16 hp briggs/statton.
Model 401707
Type 013401
Code 8002212
Engine timing seem advanced throttle up is slow and backfires through the carb. How do i set timing besides a new flywheel