Should it return to base?

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86Z28, GM 350, Jet perf Q-jet & chip Dual snorkel air cleaner, Edelbrock performer intake, Edelbrock headers, Edelbrock cat-back, Off road pipe, MSD 6AL, Accel Super Coil, Moroso Blue max wires, Rapid fire plugs, Jet fan switch, World class t-5, Hurst Short Throw Shifter, Ram Flywheel, Center force dual friction clutch,Aluminum drive shaft, BW disc rear 3.45's & a posi, PBR calipers, Earls braided brake lines, Polygrapite bushings all the way around, poly tranny mount & torque arm mount, Hotchkis lower control arms & panhard rod, Rancho limiter straps, KYB struts & shocks, Gm Wonderbar, Edelbrock strut tower brace, SSM sub frame connectors, Jamex lowering springs, Carbon metallic brake pads, Crossed drilled rotors, Mobil 1 Tranny fluid & motor oil, GM syntheic rear end oil, K&N, Grant stering wheel, 1,200 watt system, Jet Black Paint, 91 Z28 rims, 92 wing, Tinted windows.

 

There should be advance left in the timing on engine overrun. It should gradually move towards base timing as the manifold pressure rises towards idle figures and rpm drops towards idle.

I have never observed real time data on the factory curve. Maybe someone with the proper equipment can let us in on the specifics of a factory timing curve.

 

BZ,

Christobal is correct. The timing should be advanced at decel, but I have no clue as to exactly how much. The MAP, TPS, and RPM are the major inputs used to calculate advance. At low MAP, and TPS, the higher RPM of decel will indicate a near maximum advance condition. The CTS and IAT/MAT sensors also play a minor part in timing offset.

Later,
Vader

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"Some Body...Someone"

 

I get a backfire above 2500 rpm, could this be due to, to much advance? the backfire is on decell only. Thanks alot

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86Z28, GM 350, Jet perf Q-jet & chip Dual snorkel air cleaner, Edelbrock performer intake, Edelbrock headers, Edelbrock cat-back, Off road pipe, MSD 6AL, Accel Super Coil, Moroso Blue max wires, Rapid fire plugs, Jet fan switch, World class t-5, Hurst Short Throw Shifter, Ram Flywheel, Center force dual friction clutch,Aluminum drive shaft, BW disc rear 3.45's & a posi, PBR calipers, Earls braided brake lines, Polygrapite bushings all the way around, poly tranny mount & torque arm mount, Hotchkis lower control arms & panhard rod, Rancho limiter straps, KYB struts & shocks, Gm Wonderbar, Edelbrock strut tower brace, SSM sub frame connectors, Jamex lowering springs, Carbon metallic brake pads, Crossed drilled rotors, Mobil 1 Tranny fluid & motor oil, GM syntheic rear end oil, K&N, Grant stering wheel, 1,200 watt system, Jet Black Paint, 91 Z28 rims, 92 wing, Tinted windows.

 

Check out your exhaust. Decel. backfires are often caused by an exhaust leak or a lack of back pressure. I don't think it would have anything to do with timing.

 

Havn't we already told you thats normal for a carbed car. Seriously though it cant be as bad as my backfire on accel.

 

I ahd the stock 305 in here a summit 350 in here and all of them where carbed motors and they did not have this problem, no matter how hard I got on them, my friends carbed 350 in and a 5 speed does not do it with the same exaust. I can keep going here, I don't think it is normal at all. The exaust has check out and there are no leaks, I have ahad a cat on off gutted and nothing changes.

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86Z28, GM 350, Jet perf Q-jet & chip Dual snorkel air cleaner, Edelbrock performer intake, Edelbrock headers, Edelbrock cat-back, Off road pipe, MSD 6AL, Accel Super Coil, Moroso Blue max wires, Rapid fire plugs, Jet fan switch, World class t-5, Hurst Short Throw Shifter, Ram Flywheel, Center force dual friction clutch,Aluminum drive shaft, BW disc rear 3.45's & a posi, PBR calipers, Earls braided brake lines, Polygrapite bushings all the way around, poly tranny mount & torque arm mount, Hotchkis lower control arms & panhard rod, Rancho limiter straps, KYB struts & shocks, Gm Wonderbar, Edelbrock strut tower brace, SSM sub frame connectors, Jamex lowering springs, Carbon metallic brake pads, Crossed drilled rotors, Mobil 1 Tranny fluid & motor oil, GM syntheic rear end oil, K&N, Grant stering wheel, 1,200 watt system, Jet Black Paint, 91 Z28 rims, 92 wing, Tinted windows.