56 Rochester 4GC: Trouble from the Start

[Beemon]

For those of us that have had the pleasure of running a 4GC on our 56 Buicks, we all have a story to tell... hesitation, bog, etc. I was doing a bit of reading today in the Product Service Manual and apparently they've always had a bog, even new. The engineers at Buick outlined some tricks to help weed out these hesitation issues, which mostly have to do with shortening the pump shot of the accelerator pump. Might be old news to some, but thought I'd share. Coincidentally, and unexpectedly, there is no mention of making changes to the WCFB, the superior carburetor.

 

I hope this helps some. I've always heard the 4GC was comparable in form and function to the WCFB, but it seems to not be the case here.

[JohnO]

My first collector car was a 60 Invicta with a Carter. After 21 years of service I had no issues and never touched it. Within the past 6 years I bought a 58 and a 61 with the Rochester 4GC. Due to driveability issues I swapped them for Carters - not correct for that same year, but close enough. I like Carters for their simplicity. It is a carb that is easy enough to rebuild and I was fortunate to find ones that were complete and not directly exposed to the elements.

[JohnD1956]

Nice  find Ben.  I have looked at that service tech manual numerous times and never saw those passages.  Worth a try

[Kosage Chavis]

Can someone explain the differences between 4GC and WCFB carbs.  Thank you.

[Beemon]

This is by observation, but they are almost identical aside from the fuel enrichment process. Basically, the WCFB uses two step up metering rods that are actuated by the throttle arm and the 4GC uses a single vacuum operated metering rod that falls down on a needle inside the enrichment jet at low vacuum (part/full throttle). The 4GC also uses lead plugs in the machine passages to seal them whereas the WCFB used what I think are rivets. In short, the lead is not friendly with ethanol and tend to leak and can potentially dislodge and fall out. I'm sure carb king and probably fill in more for you.

[avgwarhawk]

16 hours ago, Beemon said:

This is by observation, but they are almost identical aside from the fuel enrichment process. Basically, the WCFB uses two step up metering rods that are actuated by the throttle arm and the 4GC uses a single vacuum operated metering rod that falls down on a needle inside the enrichment jet at low vacuum (part/full throttle). The 4GC also uses lead plugs in the machine passages to seal them whereas the WCFB used what I think are rivets. In short, the lead is not friendly with ethanol and tend to leak and can potentially dislodge and fall out. I'm sure carb king and probably fill in more for you.

 

 

I have read other forums that confirm the lead will fall out.   

[avgwarhawk]

This is a good write up for things to check:

 

  http://www.thecarburetorshop.com/Troubleshooting.htm

 

 

If I'm not mistaken, the manual states that while in drive the idle should be low enough that the transmission converter should not move the car forward.  Anyone please correct me if I'm wrong.  Now, as these engines get older and all the fiddling done over the years the idle has more than likely been set higher to smooth out the engine and compensate for other worn parts, etc.  With that in mind and reading the write up in the link above,  the throttle plates are not where they need to be any longer.  Note in the write up the throttle plate position.