BenPerfected

On a couple of different threads I have made comments on my idle quality in and out of gear. Currently, I belive most of idle issues are under control. The biggest problem turned out to be the mechanical advance MSD ignition. We tried numerous adjustments but ended up locking out the timing. With my cams, starting the engines with the timing locked 40 degrees works...I was concerned that it might be a problem but they start fine hot or cold. I do agree that the Mercury Thunderbolt ignition is a better system but the locked out MSD does work with my combination.
Bottom line, most of our idle issues were related to ignition/timing not the fuel system.
I am still polishing on the the final idle RPM in and out of gear....more posts on the final fuel tuning results in 2009 as I am finished boating for 2008.

ezstriper

the mallory unilite has a great advance adj. you can adj the advance simply by popping up the breaker plate and loosening 2 screws and adj from 20 deg to lock....much neater set up than msd....have mine adj so I have only 10 deg advance works great..Rob

bcarpman

BenP, I'm not going to question that running more advvance at idle made a huge improvment in idle to in gear transitions (I'm sure it did), but I will suggest that there "might" be downsides.

The problem is, running locked out advance means way too much advance if you load the engine getting on plane at low RPM. I that scenerio, you WILL be over advanced and run into knock. This probably won't be a problem, as the prop will probably slip anyway and bring you to a higher RPM where the engine can tolerate more advance, but it "could" be an issue.

This is why automotive distributors have vacume advance, so that you can run more advance at idle and then when you get into the throttle (less vacume) the distributer will retard the timing at low rpm. EFI systems where the computer controls the spark will also do the same thing.

With my crane ignition box, I was able to compromise and run a "high Idle" spark curve where the spark is 24 deg at idle and advances to 34 at 3000 rpm.

Again, not saying you shouldn't do what you are doing, but if you ever find that you are getting into the throttle below 2500 rpm, realize you are WAY over advanced for that condition and you will be generating engine damaging knock over time.

PatriYacht

I have also read about a new completely electronic programable MSD distributer. No mechanical advance or weights. Dial in whatever advance you want.

BenPerfected

I agree that locking out the timing advance in a marine application is not great. In my boat, the RPM is 3500-4000 getting on plane with B-1's and a high X. I am always (almost) above 3000 RPM at cruise. I can see your point about detonation issues at full advance under load at 2500 RPM...like in 6'+ footers crawling home. I know...I know, you Apache guys love this ****!
IMO, the MSD mechanical advance ignition sucks for marine. I guess MSD doesn't see enough sales opportunity to make an electronic advance marine based system.
Ian, I have seen the non-maine MSD electronic advance system but it is not CG approved. Today, I am so pleased that my idle is better I haven't looked to switch...yet! For now, I am going to stay locked out, but this setup is a band aid at best.
Carp, your advance looks to be very close to the curve in the Mercury V-6 ignition box.

happy hours

Might be silly question but where do you guys run the O2 sensor for the A/F meter?

BenPerfected

I have CMI installed O2 bungs (one per engine) in the outside tail pipes close to the header flange. This gives me a reading on each bank. I have CMI Sport Tubes.