Smoke from the carb? - The 1947 - Present Chevrolet & GMC Truck Message Board Network

DoobieBrother · 07-29-2007, 08:49 PM

Well I had an interesting find today. Went out to the old `68 to drive it back around to the driveway. Parked it and decided to pop the hood to WD40 a few things just for good measure till resto starts. Anyway I'm looking around under the hood and I see this little bit of smoke coming from an open line on the back of the carb. I'm guessing it's not a big deal but wanted to run it passed you guys. It was just a little bit wafting from it like you just blew out a candle.

FYI, this is a 350 crate moter that was put in about 10 or so years ago when it belonged to wifey's grandfather. They hung all the old original crap that came on the original327. So, it's an old 2 barrell Rochester carb you're looking at from the driver side. Here's a couple of pics.

Further away for perspective...

Aarons72s · 07-29-2007, 09:43 PM

I know the 2 barrel small blocks had a crossover from the exhaust cast in the intake that the carb sits on. I gues it is used to warm the carb when it is cold.It may be coming from that. As my naighbor had a 68 307 2 brl. And he broke one of the studs off that held the carb to the intake and it had exhaust coming out there. So that is probably what you see is exhaust.

ChevLoRay · 07-29-2007, 10:28 PM

When it is running can you feel vacuum at that port? Does it pull your finger (not THAT way)? I can't think of anything at that point that doesn't have vacuum associated with it. But to my way of thinking you might see a little bit of vapor come from it after you shut it off. While it is running, you shouldn't see anything....unless it is blowby.

If it needs a vacuum hose connected, how does it run? I'm thinking you would have a vacuum leak and that it would run rough.

DoobieBrother · 07-29-2007, 11:00 PM

Runs nice and smooth. I'll have to fire it up again and see if it has any pull. I was thinking it was some kind of vacuum, but not sure. Have to check it out.

Ok. Went out and fired it up. It's definitely vacuum. It sucks your finger while it's running. In fact, if you plug it, the idle drops quite a bit. Feels like it pulls the idle all the way down to like 350-400 where it starts to lope.

07-29-2007, 08:49 PM	#1
DoobieBrother Registered User Join Date: Aug 2006 Location: US Posts: 184	Smoke from the carb? Well I had an interesting find today. Went out to the old `68 to drive it back around to the driveway. Parked it and decided to pop the hood to WD40 a few things just for good measure till resto starts. Anyway I'm looking around under the hood and I see this little bit of smoke coming from an open line on the back of the carb. I'm guessing it's not a big deal but wanted to run it passed you guys. It was just a little bit wafting from it like you just blew out a candle. FYI, this is a 350 crate moter that was put in about 10 or so years ago when it belonged to wifey's grandfather. They hung all the old original crap that came on the original327. So, it's an old 2 barrell Rochester carb you're looking at from the driver side. Here's a couple of pics. Further away for perspective...

07-29-2007, 09:43 PM	#2
Aarons72s Registered User Join Date: Apr 2006 Location: oklahoma Posts: 10,669	Re: Smoke from the carb? I know the 2 barrel small blocks had a crossover from the exhaust cast in the intake that the carb sits on. I gues it is used to warm the carb when it is cold.It may be coming from that. As my naighbor had a 68 307 2 brl. And he broke one of the studs off that held the carb to the intake and it had exhaust coming out there. So that is probably what you see is exhaust.

07-29-2007, 10:28 PM	#3
ChevLoRay Old Skool Club Join Date: Jun 2001 Location: Benton, AR "The Heart of Arkansas" Posts: 10,880	Re: Smoke from the carb? When it is running can you feel vacuum at that port? Does it pull your finger (not THAT way)? I can't think of anything at that point that doesn't have vacuum associated with it. But to my way of thinking you might see a little bit of vapor come from it after you shut it off. While it is running, you shouldn't see anything....unless it is blowby. If it needs a vacuum hose connected, how does it run? I'm thinking you would have a vacuum leak and that it would run rough. __________________ Member Nr. 2770 '96 GMC Sportside; 4.3/SLT - Daily driven....constantly needs washed. '69 C-10 SWB; 350/TH400 - in limbo The older I get, the better I was.

07-29-2007, 11:00 PM	#4
DoobieBrother Registered User Join Date: Aug 2006 Location: US Posts: 184	Re: Smoke from the carb? Runs nice and smooth. I'll have to fire it up again and see if it has any pull. I was thinking it was some kind of vacuum, but not sure. Have to check it out. Ok. Went out and fired it up. It's definitely vacuum. It sucks your finger while it's running. In fact, if you plug it, the idle drops quite a bit. Feels like it pulls the idle all the way down to like 350-400 where it starts to lope. Last edited by DoobieBrother; 07-29-2007 at 11:36 PM.



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