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#1
03-30-2005, 06:26 AM
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I'm looking for answers or places to start with a problem I've run into recently. I'm running a '69 400 in a '79 Trans Am, stock bottom end, harland sharp roller rockers, crane magnum pushrods, dual crane springs, 067 Cam, edelbrock performer intake, 800 cfm quadrajet, HEI with crane HI-6 and external coil, headers... my question is I just replaced the pushrods with the ones mentioned above, since the dual springs destoyed the previous non-hardened ones and I set up the timing as Wallace describes on his website (12 degrees initial, full manifold vaccuum to vaccuum advance) and I've noticed the idle is jumpy, as in it surges from about 750 to 800 then down to 650 and does it fairly rythmically. This problem began before I changed the vaccuum advance so I doubt I can blame that. I'm thinking it might be a dirty carb or bad plugs or wires or cap and rotor. Before I go tearing into things can anyone offer a suggestion? Thanks in advance.
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1964 Cutlass 442 Convertible (425ci Olds) 1979 Trans Am '69 400 w/TH350 3.23 Posi 1987 Cutlass Supreme Brougham (307ci Olds) |
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#2
03-30-2005, 06:26 AM
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I'm looking for answers or places to start with a problem I've run into recently. I'm running a '69 400 in a '79 Trans Am, stock bottom end, harland sharp roller rockers, crane magnum pushrods, dual crane springs, 067 Cam, edelbrock performer intake, 800 cfm quadrajet, HEI with crane HI-6 and external coil, headers... my question is I just replaced the pushrods with the ones mentioned above, since the dual springs destoyed the previous non-hardened ones and I set up the timing as Wallace describes on his website (12 degrees initial, full manifold vaccuum to vaccuum advance) and I've noticed the idle is jumpy, as in it surges from about 750 to 800 then down to 650 and does it fairly rythmically. This problem began before I changed the vaccuum advance so I doubt I can blame that. I'm thinking it might be a dirty carb or bad plugs or wires or cap and rotor. Before I go tearing into things can anyone offer a suggestion? Thanks in advance.
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1964 Cutlass 442 Convertible (425ci Olds) 1979 Trans Am '69 400 w/TH350 3.23 Posi 1987 Cutlass Supreme Brougham (307ci Olds) |
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#3
03-30-2005, 07:05 AM
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Move your vacuum advance to a ported source. It should help.
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12.84 @ 106.89 with street radials. 12.63 @ 108.39 on drag radials. |
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#4
03-30-2005, 07:20 AM
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Except for this problem existed prior to changing to full manifold vacuum. Additionally I checked the intake vacuum and it read 19# at idle which I'm sure is satisfactory for this cam.
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1964 Cutlass 442 Convertible (425ci Olds) 1979 Trans Am '69 400 w/TH350 3.23 Posi 1987 Cutlass Supreme Brougham (307ci Olds) |
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#5
03-30-2005, 08:45 AM
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Ive run into this problem with my 83 Toyota truck and the mechanic thinks the valves need to be readjusted. The idle fluctuates every 3 seconds.
-Don
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 1966 GTO 1966 421-9.3-1 comp-Race Tec 23cc Pistons 1966 Tri-Power 1967 670 Heads Pontiac "Highlift" TriPower Cam by SpeedPro DUR 214 Int 224 Exh @.050 - 107 ICL LIFT .445" Int .465" Exh Tri-Y-Headers by Tribal Tubes w/ Goerlich Mufflers 1966 Muncie Wide Ratio 4-Speed 1968-72 Chevy 12 Bolt Rear End w/ 3.73 rear gears |
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#6
03-30-2005, 09:01 AM
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Might check the float or float level in that Q-jet. The old cork style were notorious for "sinking".
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 ECM member. 2008 Outlaw Pontiac Drag Series Champion MANDRA Do it now fool! Life is short. 69 Grand Prix/3163lbs / IAII 535 w/ Tiger heads by Gaydosh....9.35@ 144 so far..  through mufflers. 1.26 60'. Going back to track with pump gas engine.... My 60 Ventura retired to street/strip duty.. |
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#7
03-30-2005, 09:40 AM
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I always start with the easy stuff first.
Look for any vacuum leaks, Cracked Vacuum line, cap missing, line that fell off. 
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Patrick -------------------------------- *SOLD * 1971 LeMans street car, 428ci TH350 3:31 12 bolt, 3880#,13.6 @ 101.82 Show & go  1964 Tempest work in progress  400 with Tremec 5 speed1967 LeMans drop top project. I tracked down my great grand father & dad's old car. |
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#8
03-30-2005, 09:52 AM
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Idle surge is often the result of lean idle fuel mix (adjust idle mix screws after verifying no vacuum leaks)
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#9
03-30-2005, 10:49 AM
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Has the carburetor ever functioned correctly with your current set-up?
If yes, and if the problem is carburetor related; it may be either too lean, or quite possibly too rich. Setting the idle with a vacuum gauge often results an irratic idle (especially if the transmission is an automatic). If you have access to the proper test equipment, check the fuel ratio at idle. Your comment that this is rhythmatic would suggest that the carburetor is maybe not the culprit. A compression test, followed by checking the ignition on a 'scope might tell you a lot. Jon.
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"Good carburetion is fuelish hot air". "The most expensive carburetor is the wrong one given to you by your neighbor". If you truly believe that "one size fits all" try walking a mile in your spouse's shoes! Owner of The Carburetor Shop, LLC (of Missouri). Current caretaker of the remains of Stromberg Caburetor, and custodian of the existing Carter and Kingston carburetor drawings. |
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#10
03-30-2005, 11:17 AM
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I guess I'll check the vacuum lines once again, however the engine makes 19lbs of vacuum at idle. I usually adjust the mixture screws using a vacuum guage and a tachometer however I'm open to suggestions on how others do it. I've checked the wires to assure that they're all seated, I've check the vacuum lines countless times as well. I may be changing weights and springs so I'll check the cap and rotor for their condition. I've performed a compression test on the engine not too long ago and resulted in two cylinders being about 10lbs lower than the rest but when the compression was @ 140lbs and went as low as 130# I didn't think it was out of the question. Thanks for the help so far.
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1964 Cutlass 442 Convertible (425ci Olds) 1979 Trans Am '69 400 w/TH350 3.23 Posi 1987 Cutlass Supreme Brougham (307ci Olds) |
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#11
03-30-2005, 06:34 PM
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Assuming you are running a PCV valve, try changing or taking out your PCV valve. Different PCV check valve weights are available. You should be able to substitute a breather, plug the vacuum line and reset your carb. If your idle smooths out, you know you will need a different PCV valve.
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71 Formula 433, Splayed cap 400 block, 4" stroke Scat forged crank, 6.8 Eagle rods, custom Autotec pistons. SD 295 KRE D ports, Old faithful hybrid roller, Torker II, Holley Sniper Stealth, Tribal Tubes, TKO 600, 3.73 Eaton posi. |
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#12
03-31-2005, 06:36 AM
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I put the vacuum guage back on last night and it read 17" so I tweaked the mixture screws and managed to get it up to 19" and it ran steady, no fluctuations. I took the car out and ran it up and down highway, getting into it and as soon as it returned to idle is seemed to be doing the same thing again. I ran a can of gum-out through it and it should be run through completely by tomorrow, hopefully I'll see a change but if I don't, any other ideas? I've been thinking of changing the PCV so maybe I'll do that as well.
__________________
1964 Cutlass 442 Convertible (425ci Olds) 1979 Trans Am '69 400 w/TH350 3.23 Posi 1987 Cutlass Supreme Brougham (307ci Olds) |
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