Base timing for 4.3GL APHUB (1995)

[ach1982]

Hello,
I want to set-up the right ignition timing of engine of my boat. It's an OMC Cobra 4.3GL APHUB from 1995. I know how to do it and I have the right shunt adapter.
But I've no idea about the right base timing for this engine. Serveral manual (V/P, Seloc, Clymer) tell different values.

I use 90AKI gas.

It would be great, if someone can help me out with the right information.

 

[alldodge]

You should have the EST distributor. Remove the 4 wire connector on the right and connect the VP timing tool 885163-6 and connect the black lead to 12V. This places the distributor in base timing mode.

If you don't have the tool, will need to connect the 2 white wires together, and hope you have a way to connect the first pin to 12V. VP is done the same as Mec, but you do not have a shift interrupter so disregard that part

 

[ach1982]

Thanks a lot for your response.
The way to set it up is what I already know, but I do not really know the right base timing value/degree.
That's what I need.
As already mentioned, the manuals contain different values for the engine of the same year.

 

[Scott Danforth]

8 degrees btdc

 

[alldodge]

Thanks a lot for your response.
The way to set it up is what I already know, but I do not really know the right base timing value/degree.
That's what I need.
As already mentioned, the manuals contain different values for the engine of the same year.

Have to agree its a mix, I'm not a VP expert but the HU manual shows 0 TDC with 89 AKI or higher. It uses the Delco EST distributor

http://boatinfo.no/lib/volvo/manuals/hu_elect.html#/16

Merc uses 8 BTDC with the TBV ignition

 

[ach1982]

I'll try 0° TDC. This is what I found in other original OMC and VP manuals. Seloc and Clymer are out of this range. I don't know why, but this is the reason why I am confused.

 

[alldodge]

If timing gets to far advanced then there can be preignition, and it can damage the motor. Using higher octane fuel allows more advance then lower octane fuels. So a Merc can use 87 and is set at 8 BTDC so when it gets distributor full advance at higher rpm will add around 20 degrees of advance.

As example
Set at TDC total advance = 30 ATDC
Set at 8 BTDC total advance = 22 ATDC

If you where to run 87 octane I would retard the timing. That said the EST distributor does have knock control to retard timing if needed, also if its working

 

[Lou C]

Agreed if you are using 87 octane gas, do not advance the timing...in my '88 OMC owners manual it lists 1* BTDC if you use regular...6* if you use premium...the other thing that is important...is total timing advance...this has to be measured at a specific rpm with the boat in neutral in the water... with an advance timing light....so...for the '88 it gives (assuming 6* base timing) an additional 12* of advance at 3200 rpm, for a total of 18*. For some reason the V6s run with less advance than the V8s...now on your '95, things could be different....not sure...how much they changed the specs...but if you get decent performance with it at 0* or 1* BTDC...then I'd set it that way...unless you wan to use premium gas...then you can go up to 6*...that's what I've run mine at all these years....with no pinging or detonation....