erratic timing

Jcris

Chief Petty Officer
Joined
Apr 23, 2016
Messages
466
Hello,
I've got a 1996 4.3 LX Gen+ Mercruiser. It's a Thunderbolt 5 ignition with a 2 barrel carb. I recently replaced the plugs, cap , rotor. Also replaced fuel/water separator and inline fuel filter. I set timing to 10 degrees BTDC at 650 rpm's while grounding the timing lead. After the tune up work I also installed a momentary switch on the fuel pump. Did that to allow manual priming of fuel bowl. After the fuel system work and momentary switch install I used the switch to prime the bowl and check for fuel leaks. No leaks so I started the engine. I did use you a good quality timing light but found the timing to be rather erratic at idle. By that I mean the timing mark seemed to float between about 8 -12 degrees. Could this be an amplifier issue? If so, how can I check it? I've checked the forums and wanted to post here.
 

Scott06

Admiral
Joined
Apr 20, 2014
Messages
6,765
Assuming you are seeing this when it is NOT locked in base mode, I think that is the way the V is supposed to work. Module adds advance and looks for an rpm change repeatedly. If rpms go up it adds more advance.

http://www.boatfix.com/merc/servmanl/16/16b4r2.pdf

Is a link to a manual outlining how the V advance works. Assuming it runs ok, If in base your timing is steady check that your advance gets 28-30 degrees total by 3500 rpm or so it's doing its job.
 

Jcris

Chief Petty Officer
Joined
Apr 23, 2016
Messages
466
Thanks Scott,
I should be able to check it again tomorrow
Jcris
 
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