Forums
NautiqueParts.comNautiqueSkins.com - Correct Craft Upholstery and Part
  New Posts New Posts RSS Feed - Carb tuning and idle setting
  FAQ FAQ  Forum Search   Register Register  Login Login

Carb tuning and idle setting

 Post Reply Post Reply   
Author
uncle-buck View Drop Down
Senior Member
Senior Member


Joined: June-14-2004
Location: United States
Status: Offline
Points: 295
Post Options Post Options   Thanks (0) Thanks(0)   Quote uncle-buck Quote  Post ReplyReply Direct Link To This Post Topic: Carb tuning and idle setting
    Posted: October-26-2022 at 9:54pm
Was tinkering with my boat engine and carb today. When the engine idle was set at 600 rpms, the engine would start right up. When the idle was reset to 650 rpms, I had to give it throttle to get it to start.
How do I get it to start with a simple turn of the key with idle set at 650 or 700 rpms? Turn the mixture screws leaner?
1990 Ski Nautique (original owner)
PCM 351W with D.U.I.
Back to Top
MechGaT View Drop Down
Senior Member
Senior Member
Avatar

Joined: March-09-2015
Location: Chattanooga
Status: Offline
Points: 271
Post Options Post Options   Thanks (0) Thanks(0)   Quote MechGaT Quote  Post ReplyReply Direct Link To This Post Posted: October-29-2022 at 6:55am
If it starts when set to idle at 600 rpm, that’s because the butterflies are choking off enough air to give a rich mixture with the amount of gas that is pulled while cranking. Setting the idle higher obviously increases the amount of air that gets by the butterflies at idle. The engine needs a rich mixture to start, hence the reason for the choke plate. You definitely don’t want to change the mixture screws to make starting a simple turn of the key. Those should be set to make a warm engine run well, use a vacuum gauge to set them. My first recommendation would be to make sure the choke plate is closing as much as possible and take it as normal to bump the throttle once to start the engine and forget about it. If you want to tinker and don’t mind the possibility of doing something that most wouldn’t then it sounds like you could try to reduce the gap between the choke plate and the air horn to make the mixture a little richer. How do you do that without cutting off to much flow? Good question. No idea if it will have some unintended consequences. You don’t want to add something temporary that could fall off and get sucked into the engine. That’s why I would say just be happy your engine runs well, bump the throttle once when starting, and enjoy.
'92 Sport Nautique
Back to Top
uncle-buck View Drop Down
Senior Member
Senior Member


Joined: June-14-2004
Location: United States
Status: Offline
Points: 295
Post Options Post Options   Thanks (0) Thanks(0)   Quote uncle-buck Quote  Post ReplyReply Direct Link To This Post Posted: October-29-2022 at 7:42am
I should have clarified. This is with a warm engine so the choke plate is not a factor.
1990 Ski Nautique (original owner)
PCM 351W with D.U.I.
Back to Top
KENO View Drop Down
Grand Poobah
Grand Poobah


Joined: June-06-2004
Location: United States
Status: Offline
Points: 9780
Post Options Post Options   Thanks (0) Thanks(0)   Quote KENO Quote  Post ReplyReply Direct Link To This Post Posted: October-29-2022 at 10:24am
Quit fiddling Buck Wink

But since you're fiddling, I'd try a little farther open on the mixture screws as a start.
Back to Top
Jonny Quest View Drop Down
Grand Poobah
Grand Poobah


Joined: August-20-2013
Location: Utah--via Texas
Status: Offline
Points: 2619
Post Options Post Options   Thanks (1) Thanks(1)   Quote Jonny Quest Quote  Post ReplyReply Direct Link To This Post Posted: October-29-2022 at 11:12am
I’ve had good luck with starting at 1 1/4  to 1 1/2 open on idle mixture screws (from lightly seated).  Start engine.  Allow engine to attain operating temperatures.  Set curb idle to 650 to 700 rpm.  Then I hook up a vacuum gauge to a full manifold vacuum port.  Then I adjust the idle mixture screws to achieve max vacuum on the gauge.  At that point, I usually richen up the mixture 1/8 to 1/4 turn.  Just the way I do it.  It’s worked well for me.  Your mileage may vary…

JQ
2001 Ski Nautique Open Bow (current)
1994 Ski Nautique Open Bow (sold)
Aqua skiing, ergo sum
Back to Top
uncle-buck View Drop Down
Senior Member
Senior Member


Joined: June-14-2004
Location: United States
Status: Offline
Points: 295
Post Options Post Options   Thanks (0) Thanks(0)   Quote uncle-buck Quote  Post ReplyReply Direct Link To This Post Posted: October-29-2022 at 3:20pm
Many thanks!
1990 Ski Nautique (original owner)
PCM 351W with D.U.I.
Back to Top
Tim D View Drop Down
Grand Poobah
Grand Poobah


Joined: August-23-2004
Location: United States
Status: Offline
Points: 2622
Post Options Post Options   Thanks (0) Thanks(0)   Quote Tim D Quote  Post ReplyReply Direct Link To This Post Posted: October-30-2022 at 6:43pm
Is the boat in the water or on the trailer?
Tim D
Back to Top
uncle-buck View Drop Down
Senior Member
Senior Member


Joined: June-14-2004
Location: United States
Status: Offline
Points: 295
Post Options Post Options   Thanks (0) Thanks(0)   Quote uncle-buck Quote  Post ReplyReply Direct Link To This Post Posted: October-30-2022 at 9:36pm
on the trailer
1990 Ski Nautique (original owner)
PCM 351W with D.U.I.
Back to Top
Tim D View Drop Down
Grand Poobah
Grand Poobah


Joined: August-23-2004
Location: United States
Status: Offline
Points: 2622
Post Options Post Options   Thanks (0) Thanks(0)   Quote Tim D Quote  Post ReplyReply Direct Link To This Post Posted: October-30-2022 at 10:04pm
Do you have the hull positioned close as if sitting in the water?  If the bow is high or low that could affect the float position.
Tim D
Back to Top
uncle-buck View Drop Down
Senior Member
Senior Member


Joined: June-14-2004
Location: United States
Status: Offline
Points: 295
Post Options Post Options   Thanks (0) Thanks(0)   Quote uncle-buck Quote  Post ReplyReply Direct Link To This Post Posted: October-30-2022 at 10:11pm
Yes. I adjust the trailer jack height. Thanks
1990 Ski Nautique (original owner)
PCM 351W with D.U.I.
Back to Top
 Post Reply Post Reply
  Share Topic   

Forum Jump Forum Permissions View Drop Down

Copyright 2023 | Bagley Productions, LLC