View Full Version : Mag 350 / Z21 Timing and Wiring

08-12-2011, 09:32 AM
Rebuilt a 350 (1993 4 bolt) to replace stock '87 350 Magnum (freeze damage) in a Z21.
Engine is .030 over with a Comp Cam CS XM 256H-12 (256 int./262 exh with 112 separation). Heads are 882 (I think that is the number, they are from the 1970's). Compression should be about 10-1 (according to machinist). Intake manifold is an Weiand with stock Quadrajet. Rebuilt stock distributor (used newer style module (wires in place of "studs"), original style superseded), Thunderbolt IV ignition and stock (GLM) exhausts (thru transom).
We have broke in the engine using Comp Cam Break-in Oil and replaced after running engine between 2,000 and 2,500 for 20 minutes (neighbors loved that). Launched boat yesterday and ran "okay" with keeping RPM in the 2,000 to 2,800 range (most of time). Does not seem to have as much power as the original setup.
Set timing at 8 BTDC at 900 RPM. Think that card needs work (was replaced a few year as ago but has sat for 2 years) as the boat "stumbles" when coming up to "plane".
Is 8 BTDC the correct setting at idle (900RPM) and how do I test total advance at WOT?
I have ONE wire that I am not sure where it attaches to. It is not in ANY Mecruiser manuals that I have seen. It is a Green wire with a White stripe. I believe that it was connected to one (either the White w/Green or the White w/Red wire). It comes from the boat wiring harness near the rear of the engine (originally I think that there were 3 wires "bolted" together that went to the distributor this one, one from the Thunderbolt module and one from the shifter interup).
Anyone have any input?