Adjusting Secondary Air Flaps

[jagness]

My secondary air flaps seem to be opening too fast. I've adjusted the spring all the way from 1/4 turn to 1 full turn incrementally. It got better as I went up, but even at 1 turn it still hesitates quite a bit when I floor it at 60 mph. I'm running a 3.91 rearend gear with a 200-4R transmission (I always turn off the lockup convertor before I try this). So at 60, I'm only turning about 2,000 rpm. I have no other problems with the carburetor. I'd appreciate advice on what else I should try. Is it okay to tighten that spring further? Here's the specs on the engine and carburetor.

Carburetor is a 17057553 off of a '77 Oldsmobile. Engine is in my '66 Olds. It's a 350 Olds with the following:
Solid lifter flat tappet cam, Duration @ .050” 239°/247°, Adv. Duration 274°/280°, Lift .561”/.544”, 110 LSA.
10:1 compression
Performer RPM intake
1.75" Headers with 3" collectors
Ported aluminum Speedmaster Heads
Progression distributor: 21* advance at idle, 35* total all in at 3,000 rpm

I built the carb with one of Cliff's kits:
Idle discharge ports: 0.099
Idle tube: 0.038
Idle down channel: 0.055
Lower idle air bleed: 0.067
Idle bypass air: 0.104
Main air bleeds (main body): 0.028
Main air bleeds (air horn): 0.070
Main jet: 0.074
Primary metering rod: 44
Power Piston Spring: Light (Cliff's orange spring)
APT: 2.75 turns out
Fuel Inlet Seat: 0.135
Float Level: 1/4”
Secondary POE well restriction: 0.039
Secondary POE restriction: 0.059
Secondary tube restriction: 0.036
Secondary hanger: G
Secondary metering rod: CV
Secondary metering rod tip: 0.041
Air Flap Open Distance: 1.300
Secondary Flap Spring: 1 turn
Choke Pull-Off Release Time: 1.5 seconds

[Cliff Ruggles]

Is the choke pull-off link adjusted so it is holding the flaps tightly closed when it is applied?

Are you using a spacer under the carb?

Any modifications to the divider in the intake?

Drop base air cleaner?

[jagness]

Thanks for your questions Cliff. They helped me think about the problem.

Yes, the pull off is holding the flaps tightly closed while it’s idling. And in case this is relevant, it pulls 10” of vacuum in park when it’s completely cold, idling on the fast idle cam at 900 rpm (it idles faster at it warms up). 11” in park completely warmed up at 800 rpm off of the fast idle cam.

I do have a 1/2” open spacer under the carb, and recently I read that you tested those and found they actually hurt performance on dual plane intakes. So I probably need to rethink that.

I did not modify the plenum divider at all.

And I actually have a 3” spacer under the air cleaner to put it up into the hood scoop. The air cleaner has a pan under it that seals to the bottom of the hood. It’s an open 14” air cleaner with a 4” tall filter element. The scoop is a copy of the 70-72 Buick Stage II hood scoop made by TA Performance. 

[77cruiser]

Did you relocate the sec. pullover hole to under the air valves, or notch the air valves?
http://www.squidsfabshop.com/gtotrain/images/2275bg.JPG

[jagness]

I did notch the air flaps like your picture. In fact, mine looks just like that picture. I didn’t relocate the pullover hole.

[novadude]

Question about those secondary rods....

I think that the CV rods are 0.0527 long tip rods?  Your specs show 0.0410?  CV rods are relatively fat on the upper portion compared to a DR, DA, CE or AX rod.  Could that be causing a bit of a lean spike when the secondary air door first opens?

[jagness]

You’re right! According to the chart in Cliff’s book, CVs are .0527. So I don’t know why my specs say .0410. I just looked through my collection of secondary metering rods and found a couple pairs of CEs, which are actually .0410. I’ll give those a try. Thanks for pointing that out!

[jagness]

novadude, the CV rods were definitely not right for this engine. I put CEs in it, and it was noticeably better right away. Then I started adjusting the spring. 3/4 was better than 1 turn. 1/2 turn was even better. I tried 1/4 turn, but I think the sweet spot might be about 3/8 turn. I’ll keep playing with it, but I’m definitely in the ballpark now.

I have a pair of CC rods too. I wonder if they’d be too rich. Any thoughts on that?

[novadude]

The CC rods are fatter on the upper portion which would make it leaner when the air door is not fully open (before you get to the power tip).  I think the CE rods are probably a better choice.

[jagness]

Okay, good to know. It’s not easy to compare them to each other with my calipers.