cooltoys61

For what it's worth I have always heard more timing will make a big difference in the low speeds but not so helpful up top. If that's true there would be no reason to risk detonation by testing the limits. Like a lot of guys here I run a V6 module to get high initial adv then it only climbs about 10deg more. Most do this for hot hot cams or superchargers to keep a good idle. I do it because my Vortec heads are not supposed to see more than 29 deg total. I'm idleing around 18 deg and running about 28 total. This is not your motor or heads so I'm not suggesting you do exactly the same. I don't even know if your MTR uses a module and guess it's the HP 20 deg adv which would still let you idle at 15 or so,,,just ramblin' here sorry

jdnca1

I always lock mine in so its always the same.

Croozin2

Active Mike, your high idle and run-on condition after running the boat may be due to a rich condition at idle. I have the same problem with my Q-jets. After making considerable changes to my 454 mags last year (including more camshaft) the vacuum signal is much weaker and thus the idle circuit in the Q-jets is almost non-existent. The problem is due to having to open the throttle plates too far to compensate for the problem in the idle circuit. I have been through every change imaginable with the Q-jets (and timing etc) and got the carbs to where I can live with them. But when I make a good run and burn all the additional fuel from the plenum and then come back to idle, the motors idle 200 - 300 rpm higher and then (naturally) try to run on when the ignition is turned off. If I idle through a long no-wake zone the motors will eventually load up again and the idle rpm drops. I am just about ready to order a pair of Sea Demons for my rig. I'm sure with a little dialog with Rum Runner I can get them dialed in perfectly.

P.S. If you've got the base timing too high you'll also usually get a grunting starter on a hot start.

cooltoys61

LPboater said 2mph diff with 37 compared to 34 not by adding Oct boost.

Active Mike

Croozin2,
That is on my to due list to go over carburetion as well.
No problems with the engine laboring to start when it gets hot. When spring breaks I will just have to do some tinkering.
Thanks for the input.

cooltoys61

Just an interesting tidbit to show that many combos are possible. An EXTREME!!! example,,,,My local machine shop told me of a race motor they just got back that wasn't running as well as they hoped,,turns out they didn't realize their timing had another 20 or so built in(think they thought it was locked in) so they were running with 55 deg total adv and didn't blow it up because they were drowning it with the carb! Please no one say I'm advocating this. Just saying the balance between fuel and adv on the top is VERY critical.

LPBoater

Active Mike -
Yeah mine do that - after a hard run they will idle at 1000-1100 for about 45 seconds and then drop down to 750 - then I usually bump them back up to 1000. I always let them idle around 1000 for a few minutes after a hard run to try an dissipate the latent heat in the motor.

Active Mike

LPBoater,
Have you done any tinkering with your boat to get rid of this problem and if so what did you end up doing?

LPBoater

No - I just deal with it - wait the 40 seconds for it to behave itself....