jaymann

hi y'all.
I'm having an ongoing battle with a bog off the line and surging at cruising speed.
The carb is a rebuilt 4GC. Ignition is Pertronix.
From a stop the car bogs right down when you step on it. If you feather the gas it doesn't. I checked the accelerator pump and the squirters and I'm getting nice strong shots from both. I checked for vacuum leaks around the carb by spraying carb cleaner and there was no change in idle so I assume no leaks.
The car also surges at a steady cruising speed. Give it some gas and it goes fine, but keep the throttle steady and it surges.
Timing is set to factory specs. Car idles smooth, starts easy.
I've searched google many times and see it's not uncommon but haven't found a solution.
Any help?

oldsmobum

My car did the exact same thing... the vacuum advance plunger was bad. If you have a vacuum tester (They are marketed as a brake bleeder, as useless as they are for that purpose) draw vacuum at the can and see if it holds. Thats how I learned mine was bad.

The vacuum advance is from a ported source- meaning little vacuum is drawn until the throttle opens up. This results in a more insignificant leak at idle if the plunger is torn.

My car stopped surging at speed as a result, but still has a bog off idle... I'm suspicious of the 60 year old carb, even though I've rebuilt it twice.

jaymann

i unhooked the vacuum advance and plugged the line. still the same surging.
i also can't figure the bog out. i don't know which is worse, almost stalling when you pull out from a stop light or the constant surging at cruising speed.
i guess the bog is worse. it's pretty embarassing having people checking out your car only to have it almost die when you pull away.

Fletch

Could be off base, but my 57 had the same problem.... original carb 4GC.. had it rebuilt Same problem... Back to rebuilder........... They changed the jets..... now no problem.. This was the original carb... jet change has to be explained by the change in newer fuel or atimized ability.
Fletch

jaymann

i fiddled with it some more today. timing makes no changes. vacuum advance hooked up or plugged makes no change. i tweaked the accelerator pump linkage so that i get a good squirt as soon as the linkage starts to move. i sprayed carb cleaner in thru the fuel line and pumped it thru the carb.
my dad took it for a drive and said it ran great. i hopped in and took it for a drive and the surging is terrible now and the damn thing stalled in the middle of the road while making a left turn. took quite a few cranks to get it going. dad was with me and couldn't believe it.
i'm about ready to remove the carb and throw it in the ocean.

rocketdownunder

Jayman i know you had the carb rebuilt but check the secondarie butterfly's in the carb they could be jamed shut and are not opening, also check your gas filter could be cloged.
cheers chris.

jaymann

the secondaries open fine. i removed the gas filter and installed a clear inline filter so i could see if it's getting fuel.
i'm starting to think there's some crud in the carb moving around. sometimes it works, sometimes it's bearable, sometimes it's down right maddening.
maybe it's time for another teardown and degunking.

rocketdownunder

The joys of owning old cars mate, but i wouldn't have it any other way but i'm thinking its a blockage of some sort, i had a simular problem,it turned out to be the secondaries jamed shut, had the carb rebuilt and wow! she purrs like a kitten now, and no hesitation of any sort, i have a awsome carby guy here did a great job, i still can't get over how nice this thing drives for its age.

euroman1

Had the bogging with my stock carb,at the end i've put a new accelerator plunger in,cleaned it again and adjusted the carb as per book.no bogging when i step in it,just squealing tires...:-))

Tedd Thompson

Had a similar problem with a quadajet in a Chevy powered Land Cruiser. Would idle but bubble and stall when given throttle till you hit the secondaries. Got it to backfire through the carb and it blew the piece of junk out of the jet. No problem for about 10 years now. Just a thought... Tedd

jaymann

ya, it's sure been frustrating but I'll take a step back and calm down
I think I'll have it rebuilt again and hope I'm not just throwing money out the window.
I may even consider swapping the carb for an Edelbrock if I can figure out the linkage.
Euroman1...I wish I could squeal the tires!

55/98

I have had the same problem with my 4gc carb, rebuilt twice, new vac cannister on distributor. What I found is that the accellerator pump is getting torn apart after just one trip to work and back.
I have like I said rebuilt it twice with different kits and got a new acc. pump from Mike's carberator for a third try on the pump but to no avail. I now has a eldlebrock on it that I re-jetted, no bog, no surging, made a bracket for throttle linkage.

jaymann

I ended up rebuilding a 600cfm vacuum secondary Holley that I had lying around and installing that just to see if it eliminated the problem. Not only does it not bog anymore, but the power gain is quite amazing. The car always felt like it was holding back. Now it ups and goes!