Engines get excited and idle high
 

I have a pair of N/A 540s and they start and run great. My question is after running them they will idle high out of gear. Eventually they will slow down to normal idle but takes a while. Both engines act the same. The problem is when you slow down after running and need to dock the engines are idling 1300-1400 out of gear and need to shift (bravos) anyone know what causes this and a cure? engines are 600 hp 620 tq at 4800-4900. 950 quick fuel carbs, 35 degrees timing

it is possible that the springs in the distributors are right on the edge. meaning that they are at full advance but you come down and they are holding the idle up because they are still full advanced. after a short time they start to pull in and the timing comes down and the idle comes down. a timing light will answer that but I have run into it more than once where the distributor was set to bring timing in quickly.

originally i had light springs and the black bushing.now i have the timing locked out . its the same both ways

I used to fix that on older holley by drilling 1 very small hole im each butterfly to let some air by. That would then allow idle speed screw to be set lower allowing idle mix screw to do it job. Maybe not the preferred way but worked for me.

my carbs have a .040 hole in each butterfly.

Sounds lean
You may have to enrichen your idle mix.. The days of achieving high idle with no load on mixture screws changes when low vacuum is present..
In gear dies then we crank up the idle to compensate.
You may need to go up in jet aswell but not sure your combo etc.. Fatten the idle setting then jet if it improves

hot oil thins out and lets the motor run at a higher idle. I see the same issue after a 30 minute run at WOT, a few minutes at idle and all is good

I never thought about the oil. that would be about the right time frame .

it could be the throttle cable adjustment.

I've seen secondary throttle blades hang up just a touch when 'closed' and take a few to work their way correctly closed....1 Holley and several BG Demons.

I agree with Mike Tkach - cable adjustment and after that dial in carb adjustments and idle adjustment

Well, if you dont come into the marina at 97 mph, the engines should have a chance to idle down. As an added bonus, you wont pizz off the blowboaters in the marina and they will stop throwing yogurt and granola at you.

Mine did that same thing, throttle adjustment.
See if you can push the throttle blades closed and if so put some more tension on the cables

or see if you can pull the throttle arm down with your fingers to bring idle rpm down while engine running - if it does then either cables need adjustment or you do not have free moving arms. Also unhook your throttle cable to see how free they move especially that last portion of movement to full return so you can get the correct idle speed .

Nah... Bring it in a little hot. Eventually the blowboaters will go somewhere else. Plus it's almost as good of entertainment as the boat launch on a busy day.

All bs aside looks like you got some good feedback. I'd start with checking all linkage and carb adjustments as well as throttle blade position at time. Cables stretch etc. No need to repeat everything already mentioned above rather just confirming I pretty much agree with most mentioned.

Just curious how many hours are on engines/carbs? Make sure both primary and secondary plates move freely. Like some have mentioned I have a feeling your throttle plates are not going back to desired position when warmed up.

Not likely since both engines are performing the same but I've seen metering block gaskets mispositioned throwing off idle circuitry.

Also what rpm when cold? Has this always been an issue? If you take your time and start process of elimination you'll get the problem solved. Without a doubt your Bravo drives will not happy if the problem persist. You don't wanna start a thread on "how to UNWELD cone clutches" or worse how to rebuild upper. Lol

Good stuff!

Engines have 50 hours and yes it's always done it. I appreciate all the ideas.

When they are in the fast idle warm condition disconnect the throttle cable from the carburetor and see if extra pressure on carb arm brings the idle down. If it does it's a cable/control adjustment, if it doesn't it's a mixture issue try adding fuel since timing is locked out. Make sure no fuel is dripping from the boosters, at idle all fuel goes through the idle circuit. If fuel is dripping the power valves are bad or float level is high.

I had the same problem few years ago on my 540's,,, after checking all linkage , etc, to get it correct,
on my MSD distributors I went one step stronger on the distributor springs, use the black bushing, 36 degree total advance,, opened the rear butterflies to .018, then readjusted the idle screws, they now idle down to 900 rpm in neutral every time when hot.

Our answer to a perfect idle was the new Holley Marine Dominators. Prior to this we fought numerous Holley Carbs including the 750, 850, 1050 and 1150 + BG's and 3 different after market carb gyros for over 20+ years. Today with pretty big cams making 700 lbs torque and 780 HP these engines now idle around the docks in and out of gear without touching the sticks. We can now idle as low as 450 RPM in gear without stalling.The next surprise with these carbs is you don't even need to re-jet or do anything except bolt them on. The real question is....how do they know?
Ben

You need to ask the Greys from Area 51. Lol. Before to long boats will cruise above the water. I'd take up badminton when that happens.

what is the idle timing set at?

If they are dominators the linkage inside could be hanging up. I would try external linkage.

Exactly! and possible cable adjustmeny

after checking the cable for holding it up, put a timing light on it and see what the timing is doing, I bet the advance is funky, also make sure the rotors are not loose, that has come up several times, I still like to lock the dist. cleans up the idle quite a bit.

Any updates on this.

IMO the easiest thing to do first is run the engine in the water - unhook the throttle cable and snap throttle to see if idle returns to normal like how it should.

back out the idle mixture screws 1/8 turn

timing is locked at 34 degrees . Im going to mess with it saturday ill try to fatten it up but it i think i have the idle screws out enough it smells strong! thanks for all the ideas

ck power valves for leaking

It's been mentioned a few times to fatten the idle up but I've seen this go both ways. I've seen that you can get a high idle on a hot engine when it's fat as well as lean. Cold and rich the idle is low but then you go for a spin and the idle is high because it's burning everything off and needs to be leaned out a little.

I start with 1 1/2 turns and then adjust everything hot. I go for a ride, then make adjustments in and out of gear while still warm and that is usually where it needs to be. If you're not getting much mixture adjustment with the bleed screws, you have to change the idle air bleeds.