Author Topic: still cannot control mixture correctly  (Read 124 times)

Offline PonchoVia

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still cannot control mixture correctly
« on: February 11, 2020, 12:56:35 PM »
17058276 Previously installed Cliff's kit, 73 jets, 44 rods, float level 17/64.

OLD SETUP:
(Engine Pontiac 400 0.040+, 96 heads, performer intake, comp 262 cam, HEI with centrifugal coming in at 1000, all in at 2900. I've been using manifold vacuum for advance. 2004r, 9 inch 3.25.)

OLD ISSUE:
Had an issue with idling like crap but driving perfectly. Called Cliff to order a choke pull off, turns out I   didn't need it. Recently installed AFR/wideband found my idle problem was WAY too lean, mixture screws did next to nothing to correct. Added Cliff's recipe to open idle down tubes and mixture holes to add fuel for the old cam which helped the idle quality, but never solved my lean issues.

NEW ENGINE:
461 forged rotating assy from Butler, Kauffman Dports, 310 cfm, Comp roller 232-238 @ 0.050, 113 LSA .590 lift with the 1.65's.

JUST got the engine put back together. STILL cannot control the mixture well at idle. I've got wide bands in both banks. Left shows fairly well around 12.1-5, right shows 15-16-sometimes 17.

Idle vacuum is 15 inches, idle quality is decent.

Swapped o2 sensors bank to bank, same readings.

Sprayed brake cleaner around idle mixture screws, right bank goes crazy, left bank not so bad, but they both get LEANER with the brake clean.

I   am concerned I   have a problem in the carb, and I   clearly do not want to hurt this engine for something silly, but I'm no guru, need some guidance.

Need some guidance for the steps to diagnose
1980 Trans Am WS6
17058276 Q-Jet, Edelbrock Performer,
400 +0.040, Comp xe264h, 8.5 compression
Ram Air exhaust
2004r by CPT, PTFB 9

Offline Cliff Ruggles

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Re: still cannot control mixture correctly
« Reply #1 on: February 12, 2020, 03:34:31 AM »
What size are the idle tubes?

DCR's?

Bypass air?

Idle airbleeds?

Offline PonchoVia

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Re: still cannot control mixture correctly
« Reply #2 on: February 12, 2020, 07:50:04 AM »
 I used .038" idle tubes, .055" DCR's and .110 idle bypass air, all airbleeds are stock.

This was info you passed on to me previously.
1980 Trans Am WS6
17058276 Q-Jet, Edelbrock Performer,
400 +0.040, Comp xe264h, 8.5 compression
Ram Air exhaust
2004r by CPT, PTFB 9

Offline PonchoVia

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Re: still cannot control mixture correctly
« Reply #3 on: February 12, 2020, 11:33:19 AM »
Just found rear vacuum tee loose. I'll fix that and recheck it.
1980 Trans Am WS6
17058276 Q-Jet, Edelbrock Performer,
400 +0.040, Comp xe264h, 8.5 compression
Ram Air exhaust
2004r by CPT, PTFB 9

Offline Cliff Ruggles

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Re: still cannot control mixture correctly
« Reply #4 on: February 14, 2020, 03:13:23 AM »
The rear vacuum T connects to both sides of the intake so it shouldn't cause one bank to show leaner than the other.

Check the power piston hanger arms to make sure one metering rod isn't deeper in the jets than the other.  I've seen hanger arms bent down enough to block off fuel flow to the idle tubes and cause lean running issues at idle speed.  Normally it's not much of a "player" at idle but keep in mind that all the fuel to the idle system has to go past the jets first so make sure everything there is set up correctly.

Also make sure the throttle plates are well sealed when closed and the shaft isn't twisted.  I see quite a few twisted primary throttle shafts from folks taking them apart without holding the parts on the choke side with pliers.  If it takes a LOT of effort to remove the screw on that side of the shaft it can get bent.  This sets one throttle plate open further than the other and messes with idle fuel delivery as different amounts of air is getting down each side at idle and the amount of transfer slot exposure isn't the same......Cliff

Offline 77cruiser

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Re: still cannot control mixture correctly
« Reply #5 on: February 14, 2020, 06:39:46 AM »
Any exhaust leaks on the lean side?
Jim