hi, i am new around here. i have my dad's first car, a 69 350 malibu. it gives off some black smoke when cold started and runs a little rough for about 5 minutes. after that, the chevelle purrs and produces no smoke. i've tried leaning out the gas mixture and new spark plugs. was better for about two weeks, but the black smoke is back. can anyone help point me in the right direction?

Welcome to TC!

You need to set the idle mixture screws when the engine is fully warmed up, and don't lean them out too much. If it's only when cold then it's probably the choke. It's getting too much choke which should be adjustable. What type of carb/choke? Stock?

If stock it could be the choke pulloff too. Its a vacuum pot that holds the choke open till the engine warms a bit. Make sure the vacuum pot has good vacuum to it. To adjust the choke pulloff you have to bend the linkage that holds the choke open to the specified clearance (between the choke door and the inside carb wall). You can get the specified clearance in a repair manual. Drill bits make good measuring tools (just don't drop them into the carb)

thanks for the tips. my dad and i adjusted the fuel mixture after warming the car up, so i doubt that is the problem. i'll try the choke vacuum.

forgot to add that everythig is stock...carb, choke, etc.

Is it for sure black smoke and not maybe a little oil burning?
I had a 78 Chev SWB that would blow a little black/blue smoke when cold because the rings were leaking a little oil. Once the truck warmed up and the rings expanded it ran fine with no smoke at all. Only on the intial start of the day after sitting overnight.

Is it for sure black smoke and not maybe a little oil burning?
I had a 78 Chev SWB that would blow a little black/blue smoke when cold because the rings were leaking a little oil. Once the truck warmed up and the rings expanded it ran fine with no smoke at all. Only on the intial start of the day after sitting overnight.
More likely valve seals I think. Seemed to be a common thing on sbc's back then.

That's what I meant, valve seals! ;-)

ok. i asked my dad what he thinks about the valve seals. he said that he never drove the car that much (it's only got 100K on it), and he really drives like a grandma. so he doesn't think that it could be the seals.

i've been thinking about changing the intake manifold and carb to a 4 barrel (currently the 350ci has a stock type 2 barrel). my dad thinks that this will clear the problem up b/c he said that the carb probably has a sticking choke.

anyways, how hard is it to replace the valve seals? i am pretty handy in general, but don't know that much about engines. would it be worthwhile to change the valve seals and seats to be unleaded fuel friendly?

If I were a gambling man, I would bet on valve seals. Valve seals have nothing to do with seats. And 100K on the engine no matter how it was driven, the possiblity of rings, seals, maybe both could be suspect. Do a leak down test and see what kind of shape your rings are in.



Rocky