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Rough Idle Disappears w/ Out Engine Cover |
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idahonautique 
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Joined: June-28-2018 Location: Idaho Falls, ID Status: Offline Points: 3 |
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 Topic: Rough Idle Disappears w/ Out Engine CoverPosted: June-28-2018 at 1:59pm |
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Hello all! I've been a lurker here for a bit over a year. I run a 1983 Ski Nautique. The boat is a little rough around the edges but starts and runs consistently. This season, I am noticing a B]rough idle, eventually the engine will stall after less than 5 min, if it hasn't been revved. Without the engine cover on, it will hum smooth in idle without issue.
Engine sounds fine at higher RPM's with or without the engine cover on. Rough idle disappears when I open the cover, which makes me think this is an air issue. I thoroughly cleaned the spark arrester thinking maybe it was dirty and restricting flow at low RPM, without any result. I've also visually examined the air intake from both ends and did not notice any blockage etc., though the intake is coming from inside the hull since the hood scoop is not attached. Would the detached hood scoop make a difference like this? Exhaust leak? Thoughts or ideas on what to try next? Thanks, |
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63 Skier
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Joined: October-06-2006 Location: Concord, NH Status: Offline Points: 4269 |
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Posted: June-28-2018 at 2:50pm |
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Hi Sam, glad to see you posting! I recommend you get a 3" hole saw and cut four holes in the doghouse.
 Just kidding, of course!I find it almost unbelievable that the doghouse seals that engine compartment so well that it affects idle, and if so why wouldn't it affect higher rpm when the need for air is much greater? I just don't know. When you say the scoop is not attached, do you mean the hose to the scoop or the actual scoop itself? I'd suggest you get that air flow back to the way it was set up originally and see how that works. Short of that, get a piece of 3/8" x 1" trim piece and cut it to fit under the front of the doghouse when it closes, that should leave a small air gap on both sides. I assume that will correct the idle same as when you remove the box. Doesn't make sense to me, but why fight it. If it does, then you know for sure that getting the air intake fixed will solve the problem. |
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'63 American Skier - '98 Sport Nautique
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scootdogydog
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Joined: November-03-2013 Location: Central MA Status: Offline Points: 404 |
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Posted: June-28-2018 at 3:31pm |
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i'd make sure the flame arrestor is clean. How does it run with the that off but the engine cover on?
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63 Skier
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Joined: October-06-2006 Location: Concord, NH Status: Offline Points: 4269 |
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Posted: June-28-2018 at 3:39pm |
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'63 American Skier - '98 Sport Nautique
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KENO
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Joined: June-06-2004 Location: United States Status: Offline Points: 11061 |
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Posted: June-28-2018 at 5:12pm |
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Is the idle speed the same with the engine box up as it is when it's down?.
Only reason I ask is because I once had an issue where the engine box when down would contact the throttle cable as it curved up from the bilge near the transmission and it was enough to change the idle due to the pressure on the cable from the box.. A little rerouting of the cable took care of that issue |
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gt40KS
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Joined: August-05-2017 Location: Wichita Kansas Status: Offline Points: 946 |
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Posted: June-28-2018 at 8:00pm |
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Are you idling with the engine compartment blower running constantly? Normally this wouldn't make a difference as the bilge blowers are not all that strong. But if there is a bit of intake blockage it seems that at a low idle the blower may be exhausting at least some of the intake air, starving the engine until more throttle overcomes the blower.
Just another thought |
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JCCI
1995 Ski Nautique GT40 |
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8122pbrainard
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Joined: September-14-2006 Location: Three Lakes Wi. Status: Offline Points: 41045 |
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Posted: June-28-2018 at 8:19pm |
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Sam,
I'm with Ken on this one. Check the throttle cable |
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idahonautique
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Joined: June-28-2018 Location: Idaho Falls, ID Status: Offline Points: 3 |
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Posted: June-28-2018 at 8:50pm |
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All, thank you for the quick feedback! I'll check the cables and make sure nothing is getting caught. I typically leave the blowers off when idling, turning them on had no effect on performance.
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Shua4242
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Joined: June-24-2018 Location: 45880 Status: Offline Points: 28 |
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Posted: June-29-2018 at 12:59am |
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I know you probably did not mess with the carb, But check the air screws on the carb and see if they are adjusted correctly, Holleys have to air screws, one on each side, do one side at a time. adjust them at idle. Turn one in until it starts making the motor run rough, then turn it out until it runs rough but counting the amount of turns, Then turn it back in to the halfway spot. Then repeat to the other side.
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SNobsessed
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Joined: October-21-2007 Location: IA Status: Offline Points: 7102 |
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Posted: June-29-2018 at 10:24am |
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Any chance this could be heat related? Cools off a little when DH is open? Maybe not enough airflow to pull heat out.
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“Beer is proof that God loves us and wants us to be happy.”
Ben Franklin |
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gt40KS
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Joined: August-05-2017 Location: Wichita Kansas Status: Offline Points: 946 |
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Posted: June-29-2018 at 2:03pm |
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Have you noticed what your temps are running during all of this? To be more accurate it would probably be best to check temps with an IR gun
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JCCI
1995 Ski Nautique GT40 |
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idahonautique wrote: