I have a '59 Rochester 4GC on a '59 283. It used to have a terrible flat spot . After being rebuilt twice by two carburator people I trust, the flat spot is 94% gone. However, When you stab it off the line, or even in first gear on a roll, there's nothing there. Like you're just driving. I'm ready to send it off to some $300 GUARANTEED carb rebuilder. I COULD buy some new Edelbrock or Holley, and enjoy it's bright, shiney, out-of- placeness. But I'm stubborn.I refuse to have a carb outwit me. I LIKE the look of my 1959 carb. These carbs ran fine for years and years. Dammit, Jim, I'm a painter,not a carb builder. Anybody got a carb guy they trust, or should I just spend the $300 ? OR just drive it as a pooch?
Secondary spring tension issue. Read this and see if it helps. http://www.thecarburetorshop.com/Troubleshooting.htm
Hope you like this and hope it gives a better understanding of this carb. http://tri5chevyg***er.blogspot.com/2009/04/rochester-4g.html Sounds like the "Auxiliary Valve" isnt openning when it should and your not getting the back barrels open soon enough. You can adjust this with an allen wrench to make those blades move at whatever rate you need.
Hesitation off the line, or even from a rolling start if at idle is normally caused by too fat an idle setting. Try leaning the idle mixture control screws, and compensate the idle RPM with the throttle positioner screw. If the engine is basically stock, about 1 turn from lightly seated will be very close. Also check the timing. Jon.
Sounds more like an accelerator pump issue to me. With the engine off, stab the throttle & make sure you see fuel squirting in the carb.
Hey guys, Picking up on an old thread here, but I've spent the past 2 weeks trying to wrap my head around 4GC problems. I'm running a 4GC on a stock cast manifold over a rebuilt 350 and an "RV" cam. I've been having the exact same issues. The problem I've had is finding a decent reference for tuning after mounting. Does anybody know of a Rochester Guru or a Rochester site that would answer questions directly about these guys? The pickup ran on this carb for the last 30 years and it doesn't seem right to just toss it for an AFB style. Thanks Echs
Since Chevrolet never put a 4-GC on a 350, you may have internal calibration issues. These are excellent carburetors, when they are properly sized and properly calibrated to the engine. If this carb originally came from a 327, it may be necessary to resize the idle tubes (especially if you are burning corn gas) as well as the main jets. Jon.
The 4GC uses a power valve like other Rochesters, I have had to cut or streach the spring in order to eliminate a "dead" spot, hesitation or bog.
Trying to figure out vacuum lines. Got the front vacuum port blocked because I couldn't get a vacuum reading there, and the motor runs better that way. Using the back port for the vacuum advance and the power brakes. Anyone have a clue about the front port? Attaching a photo.
Idle mix screwsboth screwed 2 &1/4 turns out(do not tighten these) ? Is your vacuum advance pod leaky ? Distributor spark port is on right side under choke ...these carbs had a flat or bog taking off and turning to the right dew to fuel transfer issue. Are your valves set to tight ? Old tappets set to just when the tapping stopes new valves set 1/2 turn down from nill with pumped up tappet (when tapping stopes)distributor weights free moving (need oiled)
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