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Engine hard to start since carb rebuild


56 Buick
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Merry Christmas all

 

I am hoping someone can assist.  Put a carb kit through the Rochester 4GC on the 56 and ever since the engine has been very hard to start. Prior the engine would fire up straight away. Didn't touch anything but the carb. Any ideas of what may be the issue?

 

Thanks

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Is the accelerator pump working? with engine not running, looking down the throat, operate the throttle, should be squirting 2 streams of gas. If not, you may have left something out, like a check-ball. When you go to start the car do you mash the accelerator pedal once, then turn the ignition on and  mash the pedal to start?

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... Also note that factory spec rebuild float adjustments as stated in the old factory book does not always equate to an optimum float movement range spec due to the cause and effect of our current pump alcohol based  (gas-o-hols, corn-hols etc. ) that is currently available at the pumps and can cause idling, loading and start up issues.   

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Have checked. Air cleaner off and pumped the gas. No stream of fuel. Took out the inspection screws from the float chambers and cant see fuel. Hmmmm not sure if I had pumped the gas after I last had the engine running but should that have drained the float chambers? Now I am confused.

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Poured fuel down throat. Started up and runs. When I twist the accelerator linkage I see fuel dribble fron the primary venturies but no streaming. Anyway, stopped the engine and then twisted the accelerator linkage again. Still no streaming seen from the 2 channels up top, only misting coming from the primary venturies. Does this mean the accelerator pump? I will need to take it off and put the old accelerator pump back in?

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4 hours ago, 56 Buick said:

Poured fuel down throat. Started up and runs. When I twist the accelerator linkage I see fuel dribble fron the primary venturies but no streaming. Anyway, stopped the engine and then twisted the accelerator linkage again. Still no streaming seen from the 2 channels up top, only misting coming from the primary venturies. Does this mean the accelerator pump? I will need to take it off and put the old accelerator pump back in?

 

There should be a steady stream of fuel from the two ports that the accelerator pump feeds.  The carb will need to be taken apart and the accelerator pump inspected.  

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New accelerator pump from carb kit is wrong size. I think I have heard somewhere that Rochester had 2 different bore sizes. Lucky I still had the old pump. Only thing I am hoping now is the size of the metal check ball at the bottom of the pump bore is the same irrespective of the large or small diameter pump ... anyone know the answer?

 

Thanks, Drew.

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Rochester actually had three different accelerator pump cylinder diameters.

 

Some of the Rochesters have a check ball at the bottom of the pump cylinder, others depend on fuel going through a vertical slot above the pump. I only remember one diameter of check ball.

 

If your old pump was leather, soak it overnight in a light machine oil, such as "3 n 1" or neetsfoot oil or I use Singer sewing machine oil on new ones. Then take a very small screwdriver, and gently work your way around the leather cup, expanding the skirt diameter.

 

Once every 3 or 4 years or so, we run across a Rochester where some previous enterprising owner had bored out the accelerator pump cylinder, increasing its volume, for a performance application.

 

Jon.

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GM made a punch tool with a cup shaped tip that fit the accelerator check ball. Giving it a light rap will "seat" the ball by reshaping the carb body where it seals (its just soft potmetal, the ball is steel). You could probably make one.

Maybe. more importantly, would be making sure the check ball is in there.

Bernie

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