MSD Ignition - setting timing curve

[brodie123]

Mercruiser 165 I/O - inline 6 with MSD Ignition Box
Base Timing: 8 degrees

My distributor finally gave up the ghost and I have replaced it with a recommended MSD 8515 dist.

This dist. comes with the option to change the springs and the advance limit

The limiter comes at 21 degrees (plus base I assume) installed but 18,25,28 are ceavail in the kit

The springs come where you can combo them or how fast it gets to the max advance above. It comes from the factory with the heaviest springs but medium and light springs are avail. You can use these in any combination.


I'm trying to find a timing curve chart or to find out the maximum advance timing for my motor.

Can anyone help me select what a good start would be for the above options?

thank you!

 

[Bondo]

Re: MSD Ignition - setting timing curve

Can anyone help me select what a good start would be for the above options?

Ayuh,.... What do the Instructions that came with it say 'bout it,..??

I'd guess where it is, is a Great place to start...

 

[brodie123]

Re: MSD Ignition - setting timing curve

I understand that I may have to play with it a bit to find the happy spot.

But does anyone know what the max total advance for tht motor is? I can only find the base timing.

I just don't want to blow her up! lol

 

[Don S]

Re: MSD Ignition - setting timing curve

Here's the curve from manual #2. 1974-'77.

 

[brodie123]

Re: MSD Ignition - setting timing curve

thank you !!!

 

[brodie123]

Re: MSD Ignition - setting timing curve

ok - so here's where I am at.

That chart shows max advance should be achieved at 2800 rpm - so I put the medium springs on which states the full advance is reached at 2900 rpm - close enough!

I have the limiter set to 21 degrees (plus base timing)

the timing curve chart for this motor at WOT should be min 25 degrees and max 29 degrees

the manual says base timing should be 6 degrees

at 6 degrees she idles rough and hard starting. She's happy at 10+. I currently have the base timing at 9 degrees - so a total of 30 degrees at WOT

Should I let it rattle at idle (not smooth running) and back off to 8 base, or up it to 10 and let it be happy??? (smooth idle)

Please let me know and thanks!!

 

[brodie123]

Re: MSD Ignition - setting timing curve

p.s. is the chart total advance or is it the chart before the base? So 6 degrees + 29 max = 35 total?

 

[dubs283]

Re: MSD Ignition - setting timing curve

the chart says to add to basic timing setting

i'm surprised the runnability changes that much with so little change in base timing - have you adjusted the carbuerator properly?? performed a full tune-up recently??

these things may help

 

[brodie123]

Re: MSD Ignition - setting timing curve

she ran well before I swapped the distributor. I'll re-tune it again once I'm settled on the timing.

So please confirm:
I need to switch the limiter to 28 degrees and set base to around 6 for a total of 34 degrees

is this right?

 

[Pete104]

Re: MSD Ignition - setting timing curve

she ran well before I swapped the distributor.

 

[Don S]

Re: MSD Ignition - setting timing curve

If it was mine, I would put the distributor in with the 21? that it comes with and see what you actually get, it may be over, it may be under that 21?. Then decide if you want the 24 or 28.

 

[picklenjim]

Re: MSD Ignition - setting timing curve

Should I let it rattle at idle (not smooth running) and back off to 8 base, or up it to 10 and let it be happy??? (smooth idle)

Please let me know and thanks!!

Your engine calls for 31-35 total advance. So with the 21* stop you can set the base timing at 10-14 degrees. Timing at total advance is critical. Timing at idle is not so critical. If it's happy at 10+ then set it at 10+ using the 21* stop. If you smoke the engine it's going to be from the timing being wronge at total advance and not idle. Performance engine builders will always set their timing with the distributor running in full total advanced position for better accuracy but to do this they have balancers that are marked up high enough in degrees BTDC. If you wanted to check yours and watch it as it advances you can get a timing tape to put on your balancer and see exactly where it is at total and what rpm it reachs total at. Just be sure to get the correct one for the diameter of your balancer.

http://www.summitracing.com/parts/MSD-8985/

 

[brodie123]

Re: MSD Ignition - setting timing curve

Thank you so much !! I will do exactly that!