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#1
06-05-2020, 03:11 PM
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Light surge at low speed driving
Recently finished restoration of 1965 GTO. Trying to get the driveability improved. Runs great at speed and acceleration. However trying to get back into to my suburban neighborhood in first or maybe second gear I get a slight surge. I started with initial timing at 18 and dropped it down to 14 which helped. I suppose I just need to get closer to the factory spec of 6 - 8 degrees. Or is it possibly over lean? Sometimes I blame the light throttle spring as sometimes I think it is self induced! One chug and my throttle foot begins oscillating.
400 Tripower 670 heads 16cc dished pistons about 9.2 CR. 4 speed. 3.23 Thanks for your input- Dave in Boise
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Shuffster 1965 GTO |
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#2
06-05-2020, 04:06 PM
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In flight school, these are called "Pilot Induced Oscillations".
14 is still a lot of timing for iron heads, but at that speed I doubt it's the problem.
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77 Trans Am, 469 w/ported E-Heads via Kauffman, matched HSD intake, Butler Performance forged rotating assembly, Comp custom hyd roller, Q-jet, Art Carr 200 4R, 3.42s, 3 inch exhaust w/Doug's cutouts, D.U.I. Ignition. 7.40 in the 8th, 11.61@116.07 in the quarter...still tuning. |
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#3
06-05-2020, 05:00 PM
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Try plugging your vacuum advance to sees if that makes difference.
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#4
06-05-2020, 05:23 PM
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Move you vac advance line from "timed/ported" to full manifold (if not already). Limit it so it can only add 10* or so. Also make sure your mechanical advance curve isn't too quick. Make sure your advance springs have enough preload so that mechanical advance doesn't start until above idle speed. You should be able to keep your initial around 12-14, depending on cam and compression.
Last edited by adynes; 06-05-2020 at 05:33 PM. |
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#5
06-05-2020, 06:33 PM
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Did you change your advance weight springs in the dist.? It could be that they are too light and your vac advance is overpowering them making the timing bounce around at lower speeds when you have higher vacuum.
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#6
06-05-2020, 08:32 PM
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Sometimes, this can be improved with an adjustment of the idle mixture screws on the center carb base. Hard to access, but can be done with a piece of rubber hose that will fit over the 5/16" hex screw heads. I preset them to two turns out.
Ideally, a vacuum gage can be used to get the optimum setting, but if you turn each screw in until the idle slows, back it off until the idle smooths, you'll be good. If the bucking remains, back out each idle screw 1/2 turn. This may solve your problem. I don't think timing is the issue.
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BONESTOCK GOATS '64 GTO Tripower Hardtop (Wife's Car) '64 GTO Tripower Post Coupe (My Car) '99 Bonneville SE Sedan |
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