i have a 305 with carb that has about 140,000 miles on it. it runs fine and all but when i first start it, a puff of white smoke comes out of the exhaust. everything works properly but i'm just wondering if this is bad and what could be the culprit

 

Most likely valve stem seals are bad. Common culprit.

 

I agree....valve stem seals are worn...I'd bet money on that....won't really hurt anything if it's just puffing some...I wouldn't worry about it.

 

i was thinking more like rings. which seems more reasonable. it would probly be best either way to just rebuild the motor since its about 22 years old and has never been rebuilt

 

Only 22 years old? Unless it's definitely showing signs of an actual problem, there's nothing to worry about yet.

 

yea well i figured if it has a problem like that instead of just holding off on it i should just get the motor rebuilt

 

if it only does it when you first start it then it is the valve seals. i am not trying to tell you what to do, but it would be a lot easier and more cost effective to just replace them and not do a full on rebuild.

 

mine let out HUGE plumes of smoke, and even burned a little going down the road, after an afternoon putting valve seals in the problem is gone. do that first, engines don't need rebuilt as often as they used to

 

if its not fouling plugs, i wouldn't worry about it. this is a common problem in small block chevy engines. mine has been doing that for 30K(since i bought it). i also wouldnt waste my time rebuilding a 305, you could rebuild a 350 and have allot more power for the same money.

 

yea i always thought about dropping one in to. thanks for your help guys

 

usalllly valve seals are BLACK or BLUE smoke guys cause its burning oil. BUT if it is burning only a little i GUESS it could be white but id consider timing, plugs first then look at the stems. plus those are easier to check first Good Luck