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Canadian Poncho Homepage -> Canadian Poncho -> 65-70 Full Size Power Train Tech Forum -> 1970 Pontiac Laurentian - carburetor
Post Info TOPIC: 1970 Pontiac Laurentian - carburetor
laurent


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1970 Pontiac Laurentian - carburetor
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I have just replaced the motor with a new crate engine from GM -a 350 small block - but car is not running smoothly.  The carb has just been rebuilt but is still rough when  idling.  Should I replace the old carburetor with a new one?



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4SPEED427


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Wow, I can't believe nobody has chimed in here.

Do you know for sure it's a carb problem?

Have you tried adjusting the idle mixture screws?

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1966 Strato Chief 2 door, 427 4 speed, 45,000 original miles 

1966 Grande Parisienne, 396 1 of 23 factory air cars (now converted to a "factory" 4 speed)
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4SPEED427


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Also, have you checked for any vacuum leaks? Is it still the same intake manifold as before the engine swap (carb to intake mismatch?)

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1966 Strato Chief 2 door, 427 4 speed, 45,000 original miles 

1966 Grande Parisienne, 396 1 of 23 factory air cars (now converted to a "factory" 4 speed)
jonathanD


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my engine would not even fire up soooo  i duck taped all the places i could be having a vacuum leak and there she goes fires right up every time now =0



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67custom


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laurent wrote:

I have just replaced the motor with a new crate engine from GM -a 350 small block - but car is not running smoothly.  The carb has just been rebuilt but is still rough when  idling.  Should I replace the old carburetor with a new one?

 Which Engine did you get, the 350 290hp ??



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laurent


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yes, I've tried that.  I had a kit put in too.  Since the new kit was installed, I'm now getting lube on the dome.  Never saw that before.



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laurent


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I'm still using the same manifold and the same carb (Rochester) but I'm seriously thinking about buying another carb.



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laurent


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That's the one - ordered it from GM dealership here.  Got it shipped from GM in Montreal, I believe.



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laurent


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I'm taking it to a garage today to have the rear springs replaced.  I'll ask them to check for a vacuum leak.  When I had it running yesterday, someone said they could hear a hissing when I had the hood up and so they thought there was a vacuum leak somewhere too.



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rabbit64cs


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are the intake and carb matched? around 67 , the 4 bbl intake had 2 small ports in the front of the intake that were heat risers to warm the base of the carb. IF the carb is not the correct style for that intake, you will get a terrible vacuum leak. simply plug the heat riser ports with a small frost plugs, or tap the 1/4 NPT .

something to check??

sorry ,, read the whole post over,, intake will not be the problem, but is the carb bse gasket the right one ??


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I'm a collector...not a builder!!Located in sunny central Saskatchewan at the lakehead!
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