Surging with a 2GC

Zeke...PA

Zeke...PA

Well-known member
OK I'm running a 8BA bored to 3 5/16, with merc manifold and crab distributor, EAB heads, PCV valve, using a 55 Chevy 265-283 Rochester 2GC. I'm presently jetted at #52, runs great except for a slight surging at steady throttle. Accelerate it goes away but soon as steady a slight surge again. I have ordered an A/F meter but was wondering in the mean time if when others changed jetting if they experienced any surging lean or rich ? Vacuum gauge shows 20" and normal operation. Also has electric choke. It seems more like a light flutter than a surge. Stuck the Pontiac version 389c.i., with #53 jets in place of the #60's that it came with, seemed a little better Thanks Zeke
 
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When it does it, try pulling the choke. See what happens, could be a lean surge at cruise.
Also try regarding the ignition. See what that does.
Do these one at a time.
Keep us posted.
Martin.
 
The 2G uses a power piston thats vacuum operated for a power valve. May need to change the spring tension on the power valve. Remove the top and push in the power piston and let it pop a couple time and it will come out. When reinstalled you stake it slightly with screwdriver etc.
Spring tension may be changed by adding tension or removing a coil etc........
Look it up under 2G Rochester Power valve in google images for some operation tips...
 
Am installing a 2GC on my 290 as we speek, However the stock jets were 64. Sounds Kinda big, but it's been a while since I ran a 2GC. I do have an AF meter, we'll see.
 
I switched to #52's from #53's.

I would suspect the PCV first. Which one are you using?

One thing to try is to open the throttle plates just a little more, and re-adjust the idle mixture screws. Screw in until you start hearing misfires, then come out 1/8 turn. The idle circuits on these affect AFR's even at cruise speeds.
 
Another thing, the bore of the Merc does not line up with the bore of the 2GC and must be either bored out or Bell mouthed to remove the lip under the idle and low speed ports. I'd recommend boring the intake out to take advantage of the larger carb. I wonder why my carb has such large jets???
 
Using the PCV made up for the 8BA's turned aluminum in the vent tube hole. I tried the #51 jet in the carb today, seems a little worse. Think I'll change to a #53 tomorrow then wait for the A/F meter.Zeke
 
Yes there was a 2GC made for the ontaic and Oldsmoble that were much larger. However they won't fit on the merc intake.
 
Ron, I think you are referring to the Large Base 2G's (from about '65 on). Even in the Small Base 2G's there were some models used for the larger Pontiac and Olds engines, that might be jetted fatter. There are also different PV's.
 
Ron, there is two 2GC with the Merc bolt pattern, one has a bigger ventury and probably the bigger main jets. I have some spec out in the shop on those carbs. Walt
 
I guess I need another stock early chebby 2GC. I have a bunch of parts and a complete big bore 2GC, but not enough to get a good carb..???
 
My first 2GC was off a Pontiac 389 and was jetted at #60, I have a 55 Chevy 265-283 carb and it was jetted at #51, my A/F meter is scheduled to be delivered today. Just have to drop the right exhaust and weld in the bung. Zeke
 
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