OK here is all the data.
1965 Chevelle / 355 Small Block
68cc #186 Cast Iron Heads
Gasket Matched / Stock Valves
Comp Cams / Hydraulic Lifters
.470" I+E Lift / 224° I+E Duration @.050
110° Lobe Center
Stock Stamped Steel Rockers 1.5 Ratio
Edelbrock Air Gap Dual Plane Intake
Mallory HEI / 8MM Wire
12°BTDC with 32°@ 2800 RPM(Vacuum Not Hooked Up)
Mallory HEI
Advance On Ported Vacuum
1 5/8 Headers / 2 1/2" Full Exhaust
Carb List# 3310-3
Holley Dual Inlet / Single Pumper
#71 Primary Jets
#25 Shooter
#72 Secondary Jets (Aftermarket add on metering plate)
Yellow lite secondary spring
Stock Mechanical Fuel Pump
160° Normal Operating Temp
3:90 Gears / 235 / 60 - 15" Tires

When I stand on the gas at idle it bogs so bad that the motor will kill if I keep my foot in it. As I'm going along @ say 2100rpm in drive and I stamp it it stumbles for about a second and a half then catches up. I tried disconnecting the vacuum secondaries by simply un-screwing and popping the linkage off the butterfly bar with no change. Any Ideas??

Thank-You

Originally posted by auto3406:
OK here is all the data.
1965 Chevelle / 355 Small Block
68cc #186 Cast Iron Heads
Gasket Matched / Stock Valves
Comp Cams / Hydraulic Lifters
.470" I+E Lift / 224° I+E Duration @.050
110° Lobe Center
Stock Stamped Steel Rockers 1.5 Ratio
Edelbrock Air Gap Dual Plane Intake
Mallory HEI / 8MM Wire
12°BTDC with 32°@ 2800 RPM(Vacuum Not Hooked Up)
Mallory HEI
Advance On Ported Vacuum
1 5/8 Headers / 2 1/2" Full Exhaust
Carb List# 3310-3
Holley Dual Inlet / Single Pumper
#71 Primary Jets
#25 Shooter
#72 Secondary Jets (Aftermarket add on metering plate)
Yellow lite secondary spring
Stock Mechanical Fuel Pump
160° Normal Operating Temp
3:90 Gears / 235 / 60 - 15" Tires

When I stand on the gas at idle it bogs so bad that the motor will kill if I keep my foot in it. As I'm going along @ say 2100rpm in drive and I stamp it it stumbles for about a second and a half then catches up. I tried disconnecting the vacuum secondaries by simply un-screwing and popping the linkage off the butterfly bar with no change. Any Ideas??

Thank-You Try increasing the accelerator pump shot

Is that a 600 CFM???
Squirter size may need to be in the .31 range also. It sounds like a lean stumble.
Brian

The carb is a 750 Vacuum secondaries and I went from a 33 shooter to a 25 with no change.

Thanks

My 72 is having the exact same problem. I also have a Holley 750 vacuum secondaries and downjetted it a little. Any help would be appreciated

Check the clearance from the accelerator pump arm to the pump itself. If there is a bit of play in it, you may be pushing your go pedal and there is a delay in when the pump shot comes in.
Brian

OK here are a few of my changes for today. Changed both the front and back jets to #68. Put in a new accelerator pump gasket. Changed secondary spring to purple and put the timing back 4º to 8º @ 600 rpm idle. Didn't help at all. The accelerator pump adjustment is right on. This may be a long shot but my operating temp is 160º. Could this be too low? What do most of you guys run?

First off...i wouldn't start changing the secondery spring yet. Your seconderies should have nothing to do with your stumble problem. Especially since you stated that it stumbles off idle. I tried running a de-tuned 750 vac carb on my mild 355 in the Elky which resulted in the same problem you are encountering. I went to a 650 cfm with no problems. What is your vaccum at idle??? You may need to put in a different power valve. I would also keep the timiing bumped upto 12 degrees or so. I am running 18 in my Velle.
Also, 160 degree engine temp should not be causing it to stumble THAT bad.
Let us know!!
Brian

First Off Thanks for all the posts! It is a HUGE help to get such great ideas. I have 10 in of vacuum @ 600 rpm in gear and I had a 4.5 power valve in it. I tried a 6.5 with no help, maybe even a little worse. I know the secondaries have no dog in this fight but when you are frustrated you begin to try things that are more "fringe" ideas I suppose. :) I do have to agree that after all is said and done a 600 cfm will most likly be the solution.
Keith

I would go with a 650 DP if you don't mind the gas guzzling that will occur.
Brian

The 3310 should work very well. I don't hink that is the problem. I suspect an accelerator pump system problem. In most cases that's where a problem like this resides. Does the squirter squirt as so as you touch the throttle. Have you checked the float level? In my bracket car, I had to raise them just a touch above the normal setting to eliminate a slight hesitation.

You might try more advance. SB seem to like a lot of it. I run my driver at 16º with manifold vacuum. I don't know that it will make much difference, but worth a try.

I'm not up on vacuum secondary carbs at all, but if they are opening too soon you might get a bog. I doubt the temperature is the problem.

I have an HT383 with a Holley 750 vac-sec and an RPM air-gap intake and have exactly the same problem you describe.
I have triple checked everything and tried increasing/decreasing the squirter and jets with no improvement. (11" vac w/8.5 pv).
I am kicking around the idea that the air-gap may not have enough plenum volume and I may try adding a 1 inch spacer.
This problem seems to be very common with the air-gap manifold. Can anyone confirm or refute that?

I read the article on the air gap before I bought it and the runner voulme was supposed to close to that of a performer. I have to admit that I'm so frustrated that I'm going to pull the 600cfm of the shelf, do a freshen up, and try that.

-----------------------

65 Chevelle
94 K1500 Blazer

Since it's both an off-idle AND while cruising bog, I doubt the problem is just in your squirter. I had the same problems on my 396 before getting a new carb, and my problem was too much play in my throttle shaft, which meant a lot of inconsistencies in how the carb drove when i stepped on it. Gas was coming out the shafts, and also air in, messing up anything the carb tried to do.

FYI, my problems went away with a new carb - might want to try that first to eliminate the carb as your sole problem. I'd bump up the timing, too, until you hear pinging then back it off about 2-3°

I noticed you've tried a lot of things already - make sure you make only 1 change at a time, then test the impact of that one change.

i to would say accelerator pump. is the check ball or orange plastic diaphram stickin in the fuel bowl and also the pump shooter has a needle valve under it sometimes they get some ***** on them and restric flow severly.and i would try to get carb back to normal stay with 45 valve and get jets back to original as in 72 in front 76 in rear and deffidently get a (stock)28 sqirter and pump it up to a 31 if needed that should solve it. also the timing issue try to get the highest idle from the distributar that you can get turn very slowly and listen carefully with these combinations of thing youl be up and running in no time. good luck

First, go spend $13 on Urich's Holley book Urich's Holley Book (http://www.amazon.com/exec/obidos/tg/detail/-/1557880522/qid=1095523614/sr=1-1/ref=sr_1_1/104-9783796-3880758?v=glance&s=books). Money spent there will save you hours of speculation and guessing.

That out of the way, I agree that it sounds like an accelerator pump circuit issue. Visually, do you see that the squirter is pumping fuel? Is there fuel leaking elsewhere? ASSuming everything is mechanically working and adjusted properly, then I'd say you need to step up to a much larger accelerator pump cam. The 750 is a fairly large carb for a mild 355, but can be made to work fine.

Urich's book has charts for the pump cams and volume of fuel they provide in the various settings. I would go back to the 31 squirter (or even larger). Follow the tuning order suggested by the book - chasing after the accelerator pump circuit can be wasted time if the float level and even idle mixtures are set right.

All that said, I don't like Holley's even bore vaccum secondary carbs. The intent of that family of carbs is to SAVE MONEY on parts. Find a good 650 or even 750 DP and you will be much happier with the performance.

HTH,
jC.

I had the same problem with my 750 on a 396. I had 31 squirters and bogged like crazy. With help from TC members, I went up to 35's. Solved the problem. Summit sells them in pairs for $8.95. I bought 35's and 37's, but didn't need to go more than the 35's. No more bog!

graemlins/waving.gif Well to start I wanted to thank everyone for all the great posts. As for my Car the problem is cured. I feel it was a combination of things. The biggest factor was the timing was not far enough advanced. The t-stat was changed from 160° to 180°. The carb was changed from a 700 cfm to a 600 cfm. As I said all of these had positive effects but, in retrospect, the timing was the true x-factor.