140 Mercruiser advanced timing ?

[trevtt600]

1978 Mercruiser 140, Delco distributor. I have a dial-back advanced timing gun. When you set the advanced timing, do you subtract the intial timing of 6 from the 35@2000 and set the gun to 29 degrees, or do you just set the gun to 35 degrees and move the distributer to match TOD. After the advanced is set, what do you do with the intial? do you go back and reset the intial, or just adjust the idle.

 

[Eric 3.7LX Alpha 1]

Re: 140 Mercruiser advanced timing ?

Setting timing at advance is done at a given rpm for total timing. This includes the initial. You can check initial after checking total but can not adjust both, either 1 or the other.

 

[trevtt600]

Re: 140 Mercruiser advanced timing ?

Is setting one better than setting the other? runs great all through the rpms range, but at WOT the engine sounds like it is pining (eating glass).

 

[Eric 3.7LX Alpha 1]

Re: 140 Mercruiser advanced timing ?

In my race car engine I use advance, in my boat I use initial. Too much advance can cause detonation as well. You are checking it at 2000 RPM but WOT is what over 4000? The distributor might be advancing even more with higher RPM's. Unless you have a high horsepower engine I would use the initial timing method.

Check for over-advanced ignition timing. Too much spark advance can cause cylinder pressures to rise too rapidly. If resetting the timing to stock specifications doesn't help, retarding the timing a couple of degrees and/or recalibrating the distributor advance curve may be necessary to keep detonation under control.

How did it run at factory specs on timing?
Detonation may also be caused by low octane gas.

 

[trevtt600]

Re: 140 Mercruiser advanced timing ?

Thanks Eric. I am going to set at initial timing and take it for a test run. We will see how that does. Thanks for the help!!