Iginition Timing stays advanced during idle

"I have a 1990 7.4L Mercruiser

"I have a 1990 7.4L Mercruiser with a Thunderbolt IV ignition that I can't get the timing to 8 deg TDC; it stays advanced at approx. 25-30 deg. BTW, the engine starts easy/immediately, idles less than acceptable with the slight cackling sound. Upon rotating the distributor clockwise in an attempt to retard the timing (and adjusting the idle to compensate), the engine barely runs and then kills. I’ve verified TDC by putting the timing marking on zero (0) deg and inserted a Bic plastic pen (eliminate metallic damage) in spark plug hold thereby feeling the top of the piston, while verifying the rotor position, which points to #1 on the distributor. And verified firing order. I've replaced the ignition sensor, dist. cap, rotor w/timing wheel, spark plugs and coil ... all Mercuiser/Quicksilver components. I did not replace the spark plug wires (8mm, three years old).
Any suggestions or comments are welcome in order to get the timing correctly at 8 deg TDC."

"Is the advance moving when yo

"Is the advance moving when you rev the motor? If not, the advance mechanism is stuck (rusted). Common problem.

Jeff"

"Thanks for you comment, but t

"Thanks for you comment, but the advance (on a Thunderbolt IV) is controlled electronicaly, by way of the Ignition Module. I've speculated this Module, but marine mechanic state, this module never goes bad and it is pricey $340. In response to you question ... advance movement during rev ... I don't know I can barely see the timing mark in the first place. It is riding very high on the damper, thereby it gets block by the water pump."

i would guess it is controlled

i would guess it is controlled by the ignition module. I got a new one from autozone for my 3.0L for 40 bucks. Not sure though.

"I found the problem. I state

"I found the problem. I stated earlier that I replaced most all components ... will Mercruiser x@#$$&x me! The "sealed" distributor cap/rotor kit was packaged wrong. It contained a distributor cap for an eight cylinder and a rotor w/wheel for a six cyclinder. Amazing ... the engine started and idled. Prior to finding my problem, I ordered an Ignition Module, which is still in the sealed box (never used), that Mercruiser won't take back because it's an electrical component. }So if somebody is looking for an 15248A1 ignition module ... send them my way."