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I know this question has a few variables but I was wondering what a good idle is on the engines at temperature.. Also what is a common idle on your performance boat?

I have twin mercury racing 525 cubic inch stroked,supercharged motors with Weiand 166 superchargers ,carbeurated Chuck Nguytten 850 4 barrels,, mercury ignition, racing cam, Merlin grumpy heads, ,non switchable stainless thru hull exhaust, fancy looking pistons , and all forged internals,

It idles quite steady at about 1100 RPM's and goes into gear smooth as glass. (has SSM #4 drives)

Is that a normal RPM?

Thanks for any input.

billy boats

Seems kind of high. A small blower like a 174 or 177 with a single 850 carb should be able to idle at 850-900 in nuetral , if your idling at 1100 your probably already out of your idle circuit

Gladhe8er

My 525 idles around 700

glassdave

iTrader: (1)

my 100% stock Merc 525 SC's idled happily rights around six hundred or so no prob.

Wobble

my carbed 600hp BBC idles about 500 on cold startup. around 700 after a run and a no-wake zone. However if I run hard then come down to idle it will idle around a 1000 or so until things cool down. Next motor will be electronically controlled for sure.

Uncle Dave

Ilmor 710

650 RPM

UD

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Hi Billy Boats,
Thanks for your suggestion on idle. Wow, I am hearing a lot of variation on idle, I thought it would just stall at 600 rps's, but I will try it out today and see.
I will try adjusting the idle lower and see how it behaves.

Also my throttles retract automatically to idle unless I keep my hands on the throttles. No hands free cruising here.
I assume this retracting throttle is a typical true race boat application.

billy boats

Disconnect your throttle cables from the carbs before trying to tune
Back off your primary and secondary idle screwS so the throttles plates are fully closed crack the rear plates open 1/4 turn and front 1/2 turn. Turn all idle mixture screws all the way in and the back out 1 1/2 turns. Start the engine and adjust the front only to get idle around 700. If you need to turn primary idle in any more than another half turn to get idle try giving secondary idle another 1/4 turn.
Once you have idle at 700 adjust your mixture screws 1/8 turn at a time. Turn screws out until the idle stops going up then back in 1/8 turn. Make sure all 4 corners are adjusted the same.
Now reset your primary idle to 700-800 in nuetral. In gear should be 600-700

F-2 Speedy

iTrader: (6)

Smith Power built 540's with BM thumpers, EFI, idle at 750, C swap firing order so its nasty good

cigrocket

iTrader: (3)

My 875hp dual demon 1050s with 10-71 blowers and intercoolers idled at 800rpm. Never had an issue. Sold the Top Gun, now I have EFI.