An odd smoking at startup problem

[corvettegreg]

I am helping a friend who has a 1970 coupe, 350-300 HP. His car would always smoke at startup. It burns clean for the first 15-20 seconds til things start to warm up, then smokes (blue) for a couple minutes until the choke kicks off, then is fine while you drive it. It sounded like typical valve seals so we borrowed the tools and changed them. The car already had umbrella seals so this isn't the first time she has been worked on (and a couple were pretty brittle). We replaced with vitron seals that go over the guide boss on the head, but do not require machining.

Well, after all that she still smokes. Since it always happens when you first start up and the heat riser is closed it always smoked on the driver side only and I wanted to try to narrow down where the problem is. I wrapped some wire around the heat riser to hold it open but now when we start the car it never smokes! If I release the riser she smokes again...almost like oil is somehow getting into the crossover passage in the intake.

Has anyone ever seen this situation? My next thought is to pull the intake but am hoping someone can enlighten me on what may be going on.

Thanks

[AKRAY4PLAY]

sounds like your intake gaskets are going south. i would pull the intake and replace them. it is pretty easy to do, and does not cost much in parts. if you can change valve stem seals, you can easily change an intake. do not use the little bridge gaskets in front and back of the intake when reinstalling the intake. i use RTV ultra black. the bridge gaskets will leak eventually, besides GM does not use them any more.

[6speeder]

" I wrapped some wire around the heat riser to hold it open but now when we start the car it never smokes! If I release the riser she smokes again..."

What is the down side of holding the riser open?

[corvettegreg]

It just takes a little longer for the choke to kick off. If I were sure it was intake gaskets I would replace them over the winter.

[AKRAY4PLAY]

if your valve seals were leaking, it would puff blue right away when cold and go away pretty quick. if your intake gaskets leak, the oil splashing on the bottom of the intake takes a little time to creep to the intake ports or heat riser port. see if there is oil in the heat riser tube between the intake and choke. that should let you know if that's the culprit or not. also look in your PCV line for oil.

ps. don't use STP oil treatment unless your motor is wore out and in need of a rebuild. that stuff glazes the **** out your cylinder walls and gums up a clean motor. it works on old motors by filling in the loose clearences but kills a good motor by promoting ring blow-by.

[muddywaters]

Just be careful using silicone on your engine( I know it's used from the factory), have a friend who worked for one of the local engine rebuild shops, he relayed to me that lots of the engines that needed work was because a string of silicone RTV was sucked into the oil passages, too much RTV squeezes to the inside of the engine, cures and falls off, I had an 88 Ford Ranger with that problem, the pick up to the oil pump looked like a can of worms.

[L48]

Changing the intake gasket is not very expensive and not that big of a job relatively speaking. I would definitely do that next