The link below is from Dons at iboats. There are Mercury factory manuals there. I have cut and pasted the timing procedure. There is no manual like factory manual.
Greg
http://forums.iboats.com/showthread.php ... %201693398SERVICE MANUAL NUMBER 25 THUNDERBOLT V IGNITION SYSTEM
90-861328--1 NOVEMBER 1999 Page 4B-5
Timing and Idle Adjustment Procedures
Setting Base Ignition Timing
1. Connect timing light (91-99379 or similar) to No. 1 spark plug wire. Connect power
supply leads, if applicable, on light to 12 volt battery.
2. Connect a shop tachometer to engine.
3. Using a jumper wire, connect the ignition system timing lead (PUR/WHT wire) to a good
engine ground (–). This locks the ignition module into the Base Timing Mode.
NOTE: Before starting engine make sure the timing tab and marks on damper are clean.
Chalk or white paint on timing marks may help visibility.
4. Start engine and run at normal idle speed. Allow engine to reach normal operating
temperature.
5. Aim timing light at timing tab, located on the timing gear cover and crankshaft torsional
damper.
6. If adjustment is required, adjust timing by loosening distributor clamp and rotating
distributor body as required until timing mark on damper or pulley lines up with the mark
on tab specified in “Specifications.” Tighten clamp and recheck location of timing mark.
7. Make sure that the distributor has been tightened. Remove the jumper wire from the
timing terminal.
8. Remove jumper wire between the timing lead (PUR/WHT wire) and ground (–).
IMPORTANT: Be sure to disconnect the jumper wire from between the ignition system
timing lead and ground (–) before attempting to resume normal operations. If the
jumper wire is left in place, the ignition module will operate in the Base Timing Mode.
This means that the additional timing advance features would not function.
9. Stop engine and remove timing light.
Adjusting Idle Mixture
The procedure for adjusting carburetor idle mixture can be found in the appropriate engine
service manual. This procedure also requires that the ignition module be locked in the “Base
Timing Mode.”
IMPORTANT: In order to properly set idle mixture, the ignition module MUST BE
locked in the Base Timing Mode. This is necessary because of the Idle Speed Control
feature that exists in the ignition module. See information on the previous pages
about this feature.
To adjust the idle mixture screw correctly, the throttle plates must be nearly closed. Please
do the following:
1. Disconnect throttle cable.
2. Set idle speed (rpm) screw so engine idles at 550-600 rpm in neutral gear.
3. Adjust idle mixture screw.
4. Reset the idle speed screw until engine idles at its recommended rpm.
5. Adjust and connect throttle cable.
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). Carb adjust is exactly as I would have done it. Why does it need adjusting? Gaskets dry out, crap accumulates in the tiny passsages, fuel quality changes, things deteriorate, etc. Eventually when you can't adjust it enough, you'll need to get a carb rebuild, but until then don't worry about it - just get out there and enjoy it!
