56 Buick Posted December 25, 2019 Share Posted December 25, 2019 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 Link to comment Share on other sites More sharing options...
56 Buick Posted December 25, 2019 Author Share Posted December 25, 2019 Runs fine once the engine fires. Link to comment Share on other sites More sharing options...
56 Buick Posted December 25, 2019 Author Share Posted December 25, 2019 Actually I lie, I changed out the starter relay with a NOS unit. But the engine cranks so it cannot be related to the relay. Link to comment Share on other sites More sharing options...
NTX5467 Posted December 25, 2019 Share Posted December 25, 2019 Curious . . . why did the carb get rebuilt if it started so easily? NTX5467 Link to comment Share on other sites More sharing options...
56 Buick Posted December 25, 2019 Author Share Posted December 25, 2019 Started well. Rough idle and hesitation on acceleration. That issue now gone but another appears. Link to comment Share on other sites More sharing options...
pont35cpe Posted December 25, 2019 Share Posted December 25, 2019 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? Link to comment Share on other sites More sharing options...
old-tank Posted December 25, 2019 Share Posted December 25, 2019 2 hours ago, pont35cpe said: When you go to start the car do you mash the accelerator pedal once... At this point the choke should be closed and it should be on the fast idle cam. It should fire right off and the choke pull off should crack the choke a bit. 2 Link to comment Share on other sites More sharing options...
56 Buick Posted December 26, 2019 Author Share Posted December 26, 2019 When you say: 8 hours ago, old-tank said: and the choke pull off should crack the choke a bit. what exactly do you mean by the choke pull-off cracking the choke? Thanks Link to comment Share on other sites More sharing options...
carbking Posted December 26, 2019 Share Posted December 26, 2019 Try this link: http://www.thecarburetorshop.com/Automaticchokes.htm The item old-tank is referring to as a choke-pull-off, I refer to as a vacuum piston. Jon. Link to comment Share on other sites More sharing options...
56 Buick Posted December 26, 2019 Author Share Posted December 26, 2019 Got it. Thanks everyone. I will go and play and see what happens. Much appreciated. Link to comment Share on other sites More sharing options...
buick man Posted December 27, 2019 Share Posted December 27, 2019 ... 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. Link to comment Share on other sites More sharing options...
56 Buick Posted December 27, 2019 Author Share Posted December 27, 2019 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. Link to comment Share on other sites More sharing options...
56 Buick Posted December 27, 2019 Author Share Posted December 27, 2019 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? Link to comment Share on other sites More sharing options...
avgwarhawk Posted December 27, 2019 Share Posted December 27, 2019 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. 1 Link to comment Share on other sites More sharing options...
56 Buick Posted December 29, 2019 Author Share Posted December 29, 2019 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. Link to comment Share on other sites More sharing options...
carbking Posted December 29, 2019 Share Posted December 29, 2019 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. Link to comment Share on other sites More sharing options...
60FlatTop Posted December 30, 2019 Share Posted December 30, 2019 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 2 Link to comment Share on other sites More sharing options...
56 Buick Posted December 30, 2019 Author Share Posted December 30, 2019 Thanks. All good and working with the old accelerator pump. Check ball definitely in there. Two nice streams of fuel now and car starts on first crank. 3 Link to comment Share on other sites More sharing options...
avgwarhawk Posted December 30, 2019 Share Posted December 30, 2019 37 minutes ago, 56 Buick said: Thanks. All good and working with the old accelerator pump. Check ball definitely in there. Two nice streams of fuel now and car starts on first crank. And that is a beautiful thing! Link to comment Share on other sites More sharing options...
old-tank Posted December 30, 2019 Share Posted December 30, 2019 On 12/29/2019 at 8:19 AM, carbking said: Rochester actually had three different accelerator pump cylinder diameters. Maybe I should check the one on my shelf... (The one and only carb that beat me) Link to comment Share on other sites More sharing options...
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