Question about Briggs & Stratton Briggs Stratton Vanguard V - Twin Vertical Ohv Engine with Electric Start 23 Hp, 1" X 3 5/32" Shaft, ModelNo. 386777 - 0036 - E1

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Have a B&S, Vanguard, 23HP motor, model 386777 with 300hrs on it. Motor starts and runs fairly well, but a fair amount of smoke is being emitted from air intake. Very evident with air cleaner removed. For the most part, smoke is whitish, not black. Checked compression. It appears 1 cylinder is getting 150, the other 90psi. Due to contortions required, may be some inaccuracy related to poor checker seal at plug hole. It seems as though the plug with the higher compression is burning richer than the one with the lower number. That is, one plug is a fair amount blacker than the other. After starting, engine has a lopping/uneven idle that clears up after a minute or so. It appears that an automated arm beneath the air intake is actually adjusting the idle. You can see it move up and down as the idle varies. Any ideas as to the reason for smoking, etc.? Thanks.

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Sounds like you have a bad set of rings on one cylinder,or a bad valve set.
the stronger compression cylinder will burn richer due to the fact that the lower compression cylinder isnt pulling a hard enough vacumme to draw in all the fuel that is dumped into the intake.when the good cylinder makes it intake stroke it pulls in the excess fuel and a fresh amount from the carb.

im leaning more towards the valve train on the bad cylinder due to the white smoke comming from the carb,if the intake valve isnt seating properly,you will have compression escaping,back feeding through the intake.but yoy should hear a popping along with the smoke,everytime the engine fires that cylinder.
hope this info helps you.

4 stroke
#1 intake stroke
exhaust valve closed,intake valve the piston is on its way to the bottom of the bore,it creates a vacumme.drawing in the air/fuel mixture from the carb.when the piston hits the bottom of its downward travel,the intake valve closes,then the next stroke comes into play.

#2 compression stroke
after drawing in the air fuel mixture,the intake and exhaust valve are both closed.the rotating momentium pushes the piston back up the cylinder,compressing the air/fuel into the cylinder.

#3 power stroke
(depending on the timing)when the cylinder reaches top dead center (tdc)in the bore.the spark plug ignites the fuel,which causes the air/fuel mix explode.that explosion forces the piston back down into the bore.when the piston travels down,this stroke is completed.

#4 exhaust stroke
after the power stroke,the piston then travels back up the bore,while opening the exhaust valve.the moving pistion then pushes the exhausted air through the exhaust chamber and out the muffler.

then the cycle starts over again.
so if you have a valve thats not seating properly,on compression stroke you will have loss of compression,on the power stroke,loss of power....forcing that ignited fuel back through the valve that isnt seated corectly(if intake) you will get white smoke and a poping sound from the carb.on the exhaust stroke it will sent exhausted air back through the intake aswell.

once again i hope this helps,id dig into the valve train on that cylinder.


Posted on Oct 25, 2010


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