1974 Merc 650 Timing Procedures

[jim in edmonds]

I have a 1974 Mercury Model 650, 65 hp, 3 cyl motor that I'm trying to figure out how to set the synchronization and timing. I bought a repair manual, but it seems to be missing more than a few details for this model. It claims that the timing is to be set for 3-5 degrees BTDC and have a max advance of 23 degrees, but doesn't go into detail on how to achieve these settings. I'm unclear if you check it while cranking the engine with the starter, engine running, idle vs. wide open throttle, etc. Can anyone provide help. It's got a placard on the flywheel identifying various degrees before top dead center, including 23 degrees.

 

[Ben Konopacky]

Re: 1974 Merc 650 Timing Procedures

Jim; do a serch of chris1956 he has a good explanation of what you are looking for..

 

[Chris1956]

Re: 1974 Merc 650 Timing Procedures

Jim, It is difficult to transcribe these details in this forum. To summerize, the synchroniziation achieves the folowing:<br /><br />Minimum idle speed is set at a good idle like 1000RPM. (Screw is called Idle Stop)<br />Carb starts to open at an initial timing (ie 5-7 degrees BTDC)<br />Engine has a max Spark advance(Screw is called Max Spark Advance). <br />Engine has a max throttle advance.(Screw is called Max Throttle)<br /><br />These are all described (not so clearly) in the Mercury OEM manual I have, and if you read them a bit, it tends to make sense. <br /><br />The hardest setting is to synch the carb opening with the initial spark advance. Basically, Start with the motor running on the muffs or in the H2O, use a timing light and advance the throttle to the initial setting. Turn off the motor and (loosen the nuts) turn the carb actuation lever (on the dist.) until it just touches the carb lever and tighten the nuts. Then set the max spark advance. I just rev it up on the muffs for a moment and set the screw to max. after that set the idle stop to give about 1000 RPM in neutral, turn off the motor and push the throttle till the carb is full open and tighten the throttle stop screw.<br /><br />IF it is still not clear, see if you can see a better manual than what you have.