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#1
09-18-2022, 01:02 PM
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Lean Carb Help
Got the car to go straight with an airbag. 1.55-1.56 60 foots.
Having a carb issue now. Had 81 front and 87 rear jets in it. Checked plugs and they are dangerously lean. Jetted fronts up to 85. Still looked lean. Car runs clean up to 5500 in first and second but if I take it to 6,000 it stutters and chokes. In high gear it crosses at 6100 and pulls clean the entier time in high. Problem is only in first and second above 5500 rpm. I know years ago the air bleeds had been messed with and changed for a different motor. Is this my problem or do I just jet the carb up more. Air was 5,000 ft and it was lean... |
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#2
09-18-2022, 01:46 PM
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What was your fuel pressure during the run?
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1967 Firechicken, 499", Edl heads, 262/266@0.050" duration and 0.627"/0.643 lift SR cam, 3.90 gear, 28" tire, 3550#. 10.01@134.3 mph with a 1.45 60'. Still WAY under the rollbar rule. |
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#3
09-18-2022, 02:11 PM
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7-8.5 lbs
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#4
09-18-2022, 03:39 PM
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Do you have a wideband AF ratio gauge ?
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1967 Firechicken, 499", Edl heads, 262/266@0.050" duration and 0.627"/0.643 lift SR cam, 3.90 gear, 28" tire, 3550#. 10.01@134.3 mph with a 1.45 60'. Still WAY under the rollbar rule. |
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#5
09-18-2022, 03:59 PM
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1) Please post what carb you are dealing with.
(List # if it is a Holley carb would help) The number is on the airhorn. Tom V.
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"Engineers do stuff for reasons" Tom Vaught Despite small distractions, there are those who will go Forward, Learning, Sharing Knowledge, Doing what they can to help others move forward. |
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#6
09-18-2022, 04:02 PM
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Quote:
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#7
09-18-2022, 04:26 PM
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Seems odd that the problem would be in 1st and 2nd gear but not in 3rd when the load is greatest on the engine and the fuel demand is highest. I would expect just the opposite. If you are running pump gas it is hard to 'read' the plugs. My experience with unleaded fuel is that even with a/f ratio in the 12s the plugs will be very clean and white after a full pass.
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69 Bird w/1970 400 block(409 cubes), #64 heads, hyd. roller, Q-jet by Jeff E., original interior, ps, pdb, th350, and 3.73 gears. Pump gas, street driven muscle. 3800 lbs. race weight. Best, 11.39 @118, my son's car. 79 T/A w/463, Scat crank, Eagle rods, Icon pistons, Lunati solid roller, 262/270, KRE 325 heads, Northwind intake, QF950 carb, full interior, ps, pdb, th350, and 3.73 gears. Pump gas, 3650 lbs. race weight. 10.68 @ 126 so far... no tuning yet. |
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#8
09-18-2022, 04:53 PM
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I'm no Holley expert but 81/87 sounds dangerously lean. my 1050 went from 86/86 to 91/90 to run hard.
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12.24/111.6MPH/1.76 60'/28"/3.54:1/SP-TH400/469 R96A/236-244-112LC/1050&TorkerI//3850Lbs//15MPG/89oct Sold 2003: 12.00/112MPH/1.61 60'/26"x3.31:1/10"/469 #48/245-255-110LSA/Q-Jet-Torker/3650Lbs//18MPG 94oct Sold 1994: 11.00/123MPH/1.50 60'/29.5"x4.10:1/10"/469 #48/245-255-110LSA/Dual600s-Wenzler/3250Lbs//94oct |
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#9
09-18-2022, 08:22 PM
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#10
09-18-2022, 08:22 PM
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Quote:
Yes I figured this would be worse in high. This is what’s leading me to believe the air bleed size is causing the problem. In high with all the load on the motor the signal is strong enough for the 45 bleed? I know it’s a dangerous game messing with air bleeds if you really don’t know what your doing Last edited by 15bhardwick; 09-18-2022 at 08:35 PM. |
| The Following User Says Thank You to 15bhardwick For This Useful Post: | ||
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#11
09-18-2022, 08:25 PM
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Took the 6.5 power valve out of the front. Blocked it. Put 90 jets in it all around.
Measured the main air bleeds. They are 45 all around. Been looking and seeing stock is closer to 30. Car is running way better than I expected. 11.15 at 118 mph in 4500 DA air and 20 mph head wind shifting at 5500 Not bad for 12.5:1 compression Iron 62 d ports Solid flat tappet cam TRW flat tops 850 DP and an old warrior intake |
| The Following User Says Thank You to 15bhardwick For This Useful Post: | ||
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#12
09-18-2022, 08:26 PM
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You did not post if you had a power valve in the carb (front or rear and what the values were).
I see you did that now. Also where the mixture screws were in the metering blocks and the Transfer Slot vs the Throttle Blades were. Did you say that the carb had been monkeyed with in the past??? Need a lot more info to help you out. Mixture screws 4781-1 should not be a 4 corner idle carb. Tom V.
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"Engineers do stuff for reasons" Tom Vaught Despite small distractions, there are those who will go Forward, Learning, Sharing Knowledge, Doing what they can to help others move forward. |
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#13
09-18-2022, 09:29 PM
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Those main air bleeds are killing your signal to your main jets and causing the lean condition. I use 28 main air bleeds in my Dominator and still use 93 front and 98 rear jets with a front PV.
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1967 Firechicken, 499", Edl heads, 262/266@0.050" duration and 0.627"/0.643 lift SR cam, 3.90 gear, 28" tire, 3550#. 10.01@134.3 mph with a 1.45 60'. Still WAY under the rollbar rule. |
| The Following User Says Thank You to AG For This Useful Post: | ||
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#14
09-18-2022, 09:40 PM
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45 is a massive air bleed opening.
Tom V.
__________________
"Engineers do stuff for reasons" Tom Vaught Despite small distractions, there are those who will go Forward, Learning, Sharing Knowledge, Doing what they can to help others move forward. |
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#15
09-19-2022, 07:41 AM
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#16
09-19-2022, 08:14 AM
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If both power valves are blocked, I'd jet up at least another 5/6 jet sizes to begin with?
Using new plugs to check the plug reading? 
__________________
John Wallace - johnta1 Pontiac Power RULES !!! www.wallaceracing.com Winner of Top Class at Pontiac Nationals, 2004 Cordova Winner of Quick 16 At Ames 2004 Pontiac Tripower Nats KRE's MR-1 - 1st 5 second Pontiac block ever! "Every man has a right to his own opinion, but no man has a right to be wrong in his facts." "People demand freedom of speech to make up for the freedom of thought which they avoid." – Socrates |
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#17
09-19-2022, 08:17 PM
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#18
09-20-2022, 12:33 AM
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6 lbs, no more.
8.5 lbs is way too much. There are reasons Holley regulators come set at 6 lbs. |
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#19
09-20-2022, 05:59 AM
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What fuel pump are you using?
It needs volume also. If it can't flow 1 gallon of gas in 30 seconds, look for another pump.
__________________
John Wallace - johnta1 Pontiac Power RULES !!! www.wallaceracing.com Winner of Top Class at Pontiac Nationals, 2004 Cordova Winner of Quick 16 At Ames 2004 Pontiac Tripower Nats KRE's MR-1 - 1st 5 second Pontiac block ever! "Every man has a right to his own opinion, but no man has a right to be wrong in his facts." "People demand freedom of speech to make up for the freedom of thought which they avoid." – Socrates |
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#20
09-20-2022, 01:36 PM
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