[Fullhouse]

In need of some suggestions-
1963 lemans-
400 ci
670 heads
098 cam
Offy 360 dual quad
AFB Pontiac 1961 3300's x 2 with progressive linkage
Points dist. 8° initial with manifold vac 20° idle and 36° at 2000 rpm
I have attempted the following jets
.086, .088, .093 (original jets)
The following rods have been used
.063x.052, .065x.055,.073x.067
All of the combinations can be adjusted to idle with any fuel ratio from 13.0-14.7 with no problem
The trouble is trying to accelerate. Acts like it is real lean... just bogs like it cant hadle the air comming in. The a/f indicates lean when I attempt acceleration in gear. Out of gear she will rev on up! Tried the top hole on accelerator pump rod...no luck.

Any suggestions?

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[tom s]

Contact 61-63 on this site for help!Tom

[tom s]

Are the rear air valves still in the carbs?Tom

[Fullhouse]

Yes, the carbs have been thoroughly cleaned and reassembled. Air valves are original, no mods to them.
Tried 61-63 and we are both stumped!

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[tom s]

Trans and gearing?Rear gear and first gear.On my stick shift cars I always have mine setup with 12 int and 36-38 total and all adv in by 2500.I dont run any vac advance untill everything dialed in.Tom

[Fullhouse]

Stock drive train (326 car), automatic trans axel 2.56 gears
I've tried 10°-12° and the starter seemed to struggle with the warm engine on restart.


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[tom s]

That 2 speed auto with that tall gear could be some of the issue.Have you tried disconnecting the front carb completely and just driving on the rear?If it bogs then I would say its a carb-timing issue.Tom

[Fullhouse]

Well, I guess a new distributor would be inorder because I do not know the history of the one currently in the car. Any recomendations for a small cap distributor?
I have attempted to drive the car but since it wouldnt accelerate I just idled back down the driveway and no I haven't disengaged the secondary carb because of the progressive linkage. Didn't tjere was a need to.

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[tom s]

The front one usually does not have much to do with driving until it starts opening.Not knowing how much you have in it I would just disconnect it to be sure.What CR,should be able to take 12.Tom

[61-63]

The main thing Fullhouse is trying to get someone to say here is what jetting and metering rods someone with an identical cubic inch engine (400cubes) and dual quad carbs (Pontiac application AFBs) is using successfully on their car with an auto trans. I initially suggested he install .086 primary jets, probably .070 secondary jets (I can't remember?), and .051x.061 or so metering rods. He hasn't really been able to drive the car on the street because of constant rain where he lives, but fiddling with the carbs in his garage he either can't get it to idle right or can't get it to take gas well blipping the carbs when he has gotten it to idle. He has switched jetting and rods, shut off the rear carb and ran it on just the rear carb, adjusted the idle mixture screws and air idle bypass screw, etc., etc. and it just will not perform well for him. I've helped dk how many people on the phone and built and delivered over seventy five Pontiac dual quad setups over the years and have never experienced what he is experiencing before. I'm stumped as is he at this point.

[61-63]

I suggested he post here in the race section because race guys usually know exactly what calibration they successfully have in their setups. Is there anyone on here running a 400 cubic inch Pontiac engine with a Pontiac application AFB dual quad setup on it? If so what jets and metering rods do you have installed? Forget the cam, compression ratio, gearing, body, and all of that stuff just the jetting and metering rods at this point we can start with that variable and then work up from there.

[Fullhouse]

Thanks for that 61-63, I went a stray from my intention with my original post, but yes it is a .060 over 400 (412 ci) and I am looking for suggestions on jet and rod combos.
Mr Tom thanks for the suggestion on possible timing issues, you very well could be on it because the different combinations of rods and jets all had the same reactions...the only common denominator is the distributor.

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[tom s]

John,how did you setup my clone carbs?I have run them on everything from 366 too 455 and never have touched them.Tom

[lust4speed]

I gather that you have 8° initial and 36° after 2,000 RPM with the vacuum advance disconnected? If the engine is balking at only 12° initial it might be a separate problem of a spun balancer (if the later type). Could the manifold could be held away from the head surface by interference with the valley pan. It should also screw up the idle ratios but maybe could be richened enough with the idle screws to bring them back in line even with the leak?

The two fours simply see half the air that a single does and at a given RPM acts like a single at half the RPM. Carburetor only sees the air going through it and doesn't care whether it is on a 326 or 462. I'd take Tom's advice and only run the back carb, and possibly go a step further and make a plate to block off the front carb. Test the back carb and then bring the front carb to the rear and test it also. If they run good independently, they really should run good in tandem.

While I have run the Offy manifold on a 428 with 96 heads, I went the economical way and harvested a pair of used 600 CFM Holley 1406's. Jetting didn't need to be changed to accommodate running two of them. Seems to me that original jetting for the 600's were 95's.

[blueghoast]

Progressive linkage don't work to well on dual offy intakes
You want both carbs working like one, Solid linkage works best.

GT.

[steve25]

If your timing checks our and you also have no vacuum leaks, then you either have the big idle air screw on the face of each carb open more then the needed 3 1/2 turns, AND or your pump shot is simply not big and sustained enough to eliminate your lean stumble condition.

You need to tune the carbs first in a 1 to 1 set up for clean hard accelerating running on the primary’s first!
This means rigging up a way to keep the secondary’s from opening.

[61-63]

No one is answering the question we posed which is what jetting and metering rods are you using on a 412 cubic inch Pontiac engine with two Pontiac application (or Edelbrock 600cfm) AFBs on it.

Fellas he's run it on only the rear carb and the front carb idle mixture and idle bypass screws screwed in all the way. He's checked for vacuum leaks and has none. Distributor vacuum advance is hooked up. He's actually gotten it to idle fine on only the rear carb, and I think both carbs at one point, and take throttle arm blips without hesitation - but then he comes back the next day and it is wonky again? He has an afr meter on it and when idling well it shows slightly rich but when he blips it the thing goes way lean- this with the accelerator pump rod in the top hole so he should be getting maximum shot there.

Tom I've done several carbs for you (I think?) and didn't record the calibration for all of them but the 750 cfm bathtub clones I did had .108 primary jets, .075 secondary jets, and .062x.068 metering rods in them. My notes say this was for a 434 cubic inch engine.

[tom s]

I ran progressive with a Offy for awhile and it acted like a factory 2-4.I have been running 3-4s since 1962 and always with progressive.Tom

[61-63]

Probably 99% of the sets I've done for people have been progressive and I've always given them their pick. Except the bathtub setups all of which have been tandem linkage.

[Skip Fix]

Just to throw this out what gas are you running? Mopar buddy with an AFR on his 68 Charger would see his car do wonky things with different fill ups, helped going to non ethanol gas.