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Denon Osterman

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Ignition timing + idle speed
« on: September 18, 2021, 03:47:01 pm »
Hi guys,

So right now timing is 10 degrees initial until 1000 RPM, then I add in 24 mechanical all in by 3000 rpm for 34 total. Runs great, but pretty sure I could have more timing and bring it in faster.

So I swapped springs to the lightest pair (was on second lightest already). No change to the 34 final, but now it's in by 2k, and starts coming in at 500 - which meant my "initial" (timing at idle) is actually closer to ~13-14.

Well, it ran a little better at a slow cruise, but couldn't idle to save it's life. Would hunt like crazy, stall frequently, all sorts of crap. I swapped back to the medium spring and all is well again. Here's my questions:

- I've done a lot of research on timing and I cannot believe that an extra ~3-4 degrees of idle timing, when it's already so low, is causing me to idle so badly. I know a lot of people lock out their timing at ~32-34 right at idle and are mostly fine, lots of people have 15-25 initial, etc. So what gives...why do I need such a ridiculously low initial timing?
- My idle speed is 800 rpm. From everything I've seen on this site, that's *really* low. I love it because it's quiet, makes it possible to dock somewhat easily, etc. Could this be why I need such retarded timing at idle? Is there any downside to idling so low?

Let me know if you need any engine specs (492 chevy, cam is a hydraulic roller ~230 @0.050, 0.600", 112 LSA, installed 4 degrees retarded) or if you've got any thoughts...thanks!

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Knightnight

  • Karma: +0/-0
Re: Ignition timing + idle speed
« Reply #1 on: September 21, 2021, 10:07:18 am »
Maybe just turn up on your idle screws to compensate for the additional timing. You can control the boat around the dock just the same, whether idling at 800rpm or 2000rpm because the bucket lever doesn't have fixed points, thus you can drop the reverse bucket 1/4,1/2 etc to control around the dock. Also when you adjust idle timing you need to also adjust idle screws and idle throttle screws. Best to use a vacuum gauge to really dial it in.

I wouldn't say there is any downside to idling at 800 vs 1000 mechanically besides noise and lack of additional thrust you get in difference of RPM for around the dock.
« Last Edit: September 21, 2021, 10:24:32 am by Knightnight »
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mash on it

  • Karma: +29/-0
Re: Ignition timing + idle speed
« Reply #2 on: September 22, 2021, 08:56:58 am »
I have mine idle at 950 ± for slight additional thrust around the docks and trailering. But she's a big girl, so slop counts for skill.

More important is total timing lead, mines at 12° initial, ~33/34° total, using the lightest springs. This was after a lake test to see how much timing lead my combo wanted.

Hope this helps.

Dan'l
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CJ/RR 212...under construction  "Pistol Annie"

Denon Osterman

  • Karma: +0/-0
Re: Ignition timing + idle speed
« Reply #3 on: September 23, 2021, 07:30:37 pm »
Hey guys,

Thanks for the replies. I adjusted the idle screws when I changed the timing - I had to back them off quite a bit to maintain the same target RPM (it had otherwise jumped up to 1100, so I had to back off the throttle plates to bring it back down to 800). Unfortunately I can't really go much higher than 800, maybe 900 max, for two reasons that combined make it not feasible. The first is that, at anything over ~900 RPM, the boat is a rocket ship coming into the dock. With the AA impeller and a pretty lightweight hull...I'm going way too fast. Problem number two is that in anything other than full forward or full reverse, water "leaks" between the reverse cover and the nozzle...and sprays the boat. If I'm only doing 800-900 RPM, this spray only really hits the transom or deck. Up at 1000+, it gets into the boat (and hits the engine / air intake...cringe!). So at anything over 800-900 RPM, it's an impossible balance between ramming the dock at speed, and soaking the engine / passengers / boat.

Dan'l, how did you find out how much total timing it wanted...increase by two degrees and wait for peak RPM to stop increasing, then back it off slightly? Or is there another trick?
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Knightnight

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Re: Ignition timing + idle speed
« Reply #4 on: September 24, 2021, 05:17:42 pm »
To find max timing you can listen for the ping or read the plugs. Check the amount of brown on top of the electrode. If it has made it way all the way down to the to the threads, you are maxed out basically.
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Denon Osterman

  • Karma: +0/-0
Re: Ignition timing + idle speed
« Reply #5 on: September 24, 2021, 07:12:52 pm »
@Knightnight thanks for the tip. I don't trust myself to listen for pinging, because a) I have no idea what it sounds like as I've never heard it before b) at WOT the noise of the engine, water, and wind is so fucking loud there's no WAY I'd be able to hear anything else.

I'm definitely good at reading the ground straps of plugs based on my experience with sleds (snowmobiles, for the california crowd...I'm all the way up in sunny Ontario, Canada...please don't kick me out ;) ), and I plan on reading my plugs once break in is done. Can you confirm if i'm looking for brown on the insulator, or on the ground strap? I'm used to wanting the colour change to be ~halfway down the ground strap, right at the bend where it goes towards the threads...I'd freak out if I saw a plug that it was all the way down where the threads are!
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mash on it

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Re: Ignition timing + idle speed
« Reply #6 on: September 24, 2021, 11:45:36 pm »

Dan'l, how did you find out how much total timing it wanted...increase by two degrees and wait for peak RPM to stop increasing, then back it off slightly? Or is there another trick?

It took 2 people.
I had a buddy of mine drive the boat.
I have jump seats next to the motor.
I sat in left side jump seat, had buddy bring it to 3000 rpm. I could see the tach, too.
Told him to keep the same throttle position.
I advanced the dizzy about 300 rpm, before it started going back down.
( No more throttle was used)
Retarded the dizzy a bit, and later checked initial with a timing light.
Left it at 12-13° initial.
Bam. Done.

Dan'l

Edit: going up river and 115° outside.
« Last Edit: September 24, 2021, 11:48:25 pm by mash on it »
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