1981 Nautique rpm issue |
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Pittgator
Newbie Joined: May-30-2018 Location: Florida Status: Offline Points: 8 |
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Posted: May-30-2018 at 3:58pm |
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I have a stock 1981 Ski Nautique with the 351w that runs great but will not turn more than 3400 RPMs. Once I take the throttle past that point the engine starts to bog down. Top speed is only 34 under the circumstances. Any ideas?
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8122pbrainard
Grand Poobah Joined: September-14-2006 Location: Three Lakes Wi. Status: Offline Points: 41040 |
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Jay,
Are the carb secondary's opening? Welcome to CCfan. If you get a chance, how about posting some pictures? A diary entry would be great as well. |
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samudj01
Gold Member Joined: March-10-2009 Location: NC Status: Offline Points: 941 |
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Check the secondaries like Pete says. Also could be timing. We had a bog and swore it was carb related and finally found it was timing.
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78 Ski Tique, 72 Skier w/302's, 93 SN w/351 & 17 GS22 w/zr409
Previous - 99 Sport Nautique w/GT40 and 87 Martinique w/351 |
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Pittgator
Newbie Joined: May-30-2018 Location: Florida Status: Offline Points: 8 |
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Thank you both. I appreciate it. I will be able to work on it this Saturday and let you know. If the secondary’s are working correctly then I will check the timing next. What should the timing be set at?
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SNobsessed
Grand Poobah Joined: October-21-2007 Location: IA Status: Offline Points: 7102 |
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Timing should be set between 8-10 BTDC at idle.
However, it is more likely the timing advance mechanism is rusty or has broken springs. You need to observe timing advance as you increase RPM. It should max out around 28 deg BTDC. |
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“Beer is proof that God loves us and wants us to be happy.”
Ben Franklin |
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Pittgator
Newbie Joined: May-30-2018 Location: Florida Status: Offline Points: 8 |
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I see that the secondary’s are opening as they should. I then checked the timing and it is 10 at idle and 28-30 max. The prop is a 4 blade with a stamp of 668 on it. Any additional ideas? 3400 max rpm and 34 mph max.
Could the prop be the issue? Thanks |
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Hollywood
Moderator Group Joined: February-04-2004 Location: Twin Lakes, WI Status: Online Points: 13511 |
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Way too much prop for that boat. Sell or trade it for a 540.
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Pittgator
Newbie Joined: May-30-2018 Location: Florida Status: Offline Points: 8 |
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Thanks, I thought that might be the case. Anyone have one for sale or know the best place to get one from?
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8122pbrainard
Grand Poobah Joined: September-14-2006 Location: Three Lakes Wi. Status: Offline Points: 41040 |
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Acme 540 from Delta one of our sponsors. How did you end up with the 668? |
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Pittgator
Newbie Joined: May-30-2018 Location: Florida Status: Offline Points: 8 |
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It was on the boat when I bought it. Not sure why.
Any idea what a used 668 is worth? |
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Jonny Quest
Grand Poobah Joined: August-20-2013 Location: Utah--via Texas Status: Offline Points: 2859 |
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The 540 mentioned by Pete is a good place to start. A good used prop in a popular size with no dings or repairs can bring $200+ Lots of props out there that sell for less than $200 though... JQ |
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Current
2003 Ski Nautique 206 Limited Previous 2001 Ski Nautique Open Bow 1994 Ski Nautique Open Bow Aqua skiing, ergo sum |
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8122pbrainard
Grand Poobah Joined: September-14-2006 Location: Three Lakes Wi. Status: Offline Points: 41040 |
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Jay, I'd take the prop back to the seller and get the $200 back from him or her. |
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Gary S
Grand Poobah Joined: November-30-2006 Location: Illinois Status: Offline Points: 14096 |
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Yea you could do that. You could end up as gator bait too
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Donald80SN
Grand Poobah Joined: January-12-2009 Location: Denver, NC Status: Offline Points: 3888 |
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Delta Propeller gives CCFan members a discount when you buy which makes them, in my opinion the best place to buy a new prop. You might find used on E-Bay or Ski It again.com. On the top left side of this page there is a Delta Propeller Banner that there is a discount code to use. DP5CCFAN08 is the code.
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1980 Ski Nautique SOLD Back to Cypress Gardens
2002 Sport Nautique, GT-40, FCT2, Cover Sports, Tower Bimini, Inc., Wet Sounds Audio System, Star Gazer Wake Edition S. 1968 Ski Nautique, Project. |
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Pittgator
Newbie Joined: May-30-2018 Location: Florida Status: Offline Points: 8 |
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So here is the latest. I bought the new 540 prop, installed it and did not change much of anything. Now it does about 3600 rpms and 36 mph. Once the throttle goes past 3/4 it starts to bog down and slow down. Checked the plugs and they look good. New wires as well.
Any ideas? |
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gt40KS
Gold Member Joined: August-05-2017 Location: Wichita Kansas Status: Offline Points: 943 |
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Spitballing here Jay ...
Not timing or advance system, as you've confirmed, and obviously not the prop so my first thought is fuel or fuel/ air related, especially given the bogging issue where it actually starts to slow down throttling passed 3/4. So is there a possibility of moisture or other junk in the fuel? Maybe sucking air either from a leaking gasket or a cracked/ worn fuel hose? I don't know my way around carburetors very well, but seems to me there could be an issue there as well. |
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JCCI
1995 Ski Nautique GT40 |
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MACS81SN
Senior Member Joined: May-27-2009 Location: NW OH / S. MI Status: Offline Points: 109 |
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Sounds like starving for fuel when secondaries start to open. I would find a temporary portable 6 gallon type tank and hook to fuel pump. This would eliminate existing fuel line, restricted anti siphon valve, fuel pickup tubing, existing gasoline, and anything else in tank. If runs ok then you have problem isolated. If not fixed, I would check fuel pump pressure.
The secondaries on my 81 and a few others I have worked started opening around 3400-3600 rpm. So if your secondaries are opening and there isn’t enough fuel this would equal a big bog and go away again when you back off a little. You would have to check pressure at this rpm though doing so at idle wouldnt do much unless it is low there too. I would expect to see 5-7 psi. Although don’t recall ever seeing this, I suppose you could have some kind of restriction in the secondary side of carb. Lastly, be careful with leaked gasoline when doing the above |
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Mark
1999 -SN - 502 Python 1981 - SN Owned 33 years - Sold 1968 - Mustang - Sold |
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gun-driver
Grand Poobah Joined: July-18-2008 Location: Pittsburgh, Pa Status: Offline Points: 4112 |
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Since you said the plugs look good I would guess it isn’t jetted to fat so my next place to look would be fuel supply. It may be starving for fuel I would check the filter and also check your anti-siphon valve for a partial blockage, If that all checks out I would check fuel pressure.
You should also consider a vacuum leak that is small enough that it only effects it when she’s drawing max air. Report back on what you find, good luck. Looks like Mac typed faster than me |
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MrMcD
Grand Poobah Joined: January-28-2014 Location: Folsom, CA Status: Offline Points: 3597 |
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It is very possible for a chunk of dirt or something to plug the secondary side of the carb without affecting the primary side so it could be a carb issue along with all the items already mentioned above.
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Pittgator
Newbie Joined: May-30-2018 Location: Florida Status: Offline Points: 8 |
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Thanks everyone. Really appreciate all the help. We are making progress. I ran the boat out on the lake with the cover off the carb and saw that the secondarys were opening but there was no fuel coming through. I pulled the carb and cleaned all the junk that was in it. Now I am getting about 4000 rpms. What should WOT rpms be on this 81 351w with a 540 prop?
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gt40KS
Gold Member Joined: August-05-2017 Location: Wichita Kansas Status: Offline Points: 943 |
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Not familiar with the 540 but generally if the boat is propped correctly, WOT should get you right up to, into the max rpm range of the engine, which in your case I believe is 4400. At 4000 I'd suspect there may still be some fuel delivery issues. Don't stop with the carb cleaning - check your fuel lines, fuel pick-up and anti-siphon. Afterward, very last thing install a new fuel filter. Don't do this until you've verified the fuel lines/ path downstream are clean and clear.
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JCCI
1995 Ski Nautique GT40 |
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Tpa6d
Newbie Joined: May-28-2020 Location: Wise, VA Status: Offline Points: 1 |
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Did you solve your problem. My boat is showing extremely similar symptoms, except no bog after 3/4 throttle. After 3/4 throttle it just has zero response
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