351 carb tuning
Printed From: CorrectCraftFan.com
Category: Repairs and Maintenance
Forum Name: Boat Maintenance
Forum Discription: Discuss maintenance of your Correct Craft
URL: http://www.CorrectCraftFan.com/forum/forum_posts.asp?TID=9212
Printed Date: September-28-2024 at 11:28pm
Topic: 351 carb tuning
Posted By: 76'SN
Subject: 351 carb tuning
Date Posted: December-14-2007 at 10:56pm
just wondering about carb adjustments for my nautique with a 351. it has a holley 670 with, what i am assuming, are stock jets. after about a day of riding, the back of the boat is covered in black exhaust deposits. and if i remember correctly on initial start-up and idling it seams so smoke somewhat. would this be carb related? i was told it could be burnt oil but just didnt sound right. i was thinking it was the carb becuase with WOT i stick around 38-40mph with a 13X13 prop. if so, should i reject or try to tweak what i have.
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hukt on fonix helpt me
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Replies:
Posted By: nuttyskier2002
Date Posted: December-14-2007 at 11:15pm
76, how many hours are on the motor? The black deposits very well can be from burnt oil. Although the smoke coming from burnt oil (from the exhaust) is bluish white there will still be heavy black sooty buildup on the back.
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95 Malibu Echelon w/Mercruiser 350 Magnum Skier
Former boats:
88 Ski Centurion Tru Trac II
59 Chris Craft Capri (woody)
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Posted By: boat dr
Date Posted: December-14-2007 at 11:17pm
Chad , we dont care how you spell it is how well you listen.......
If it is indeed the stock Holley it is a model 4160 with a cfm of 600.
And yes the black soot on your transom could be related to the low speed or idle cicuit being to rich.
A vacuum gauge gives the best results , highest reading in gear that will allow for instant starts without adding Any throttle will give you a cleaner transom.
This is not hard to do but requires a little patience, 3/4 round out will give you a good starting point.........Boat dr
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boat dr
/diaries/details.asp?ID=4631 - 1949 Dart
/diaries/details.asp?ID=1533 - 1964 American Skier
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Posted By: 79nautique
Date Posted: December-15-2007 at 2:11am
3/4 turn seems a little lean to me. But besides the carb if the plugs aren't gap right and in good shape, plus the timing and spark energy, aka bad coil then it all adds up so first a good tune up needs done then you can worry about the jets. So first things first, new plugs, cap, rotor, wires, proper idle mixture screw settings and idle rpm. once those are correct and you still have the shoot then we can look at the jets. But if the CFM of the carb is too much for the motor nothing will fix it but a new carb with a lower CFM rating.
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http://www.correctcraftfan.com/diaries/details.asp?ID=756&sort=&pagenum=1&yrstart=1979&yrend=1979 - 79 nautique
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Posted By: 76'SN
Date Posted: December-15-2007 at 8:15am
i knew it need a little attention as far as tune up is concerned since the person i bought it from a year or two ago ran it very seldom. they replaced the stock carb with what is on there now, which i looked up and found it was a 670 CFM. since they carb was diff i figured thats where i should start. i havent changed cap, rotor, wires, or checked initial timing. all i did was change plugs, oil and set idle because i was ready to ride when i got it and never have gotten around to anything else. and yes the smoke has a blue color to it. so im assuming start with the ignition overhaul and then the carb since im not really carb tuning inclined. thanks for the input
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hukt on fonix helpt me
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Posted By: 79nautique
Date Posted: December-15-2007 at 11:53am
Well with the color of the smoke that's bad valve guide seals or rings. Basically it's burnt oil and no amount of carb tuning is going to fix it, but tune it up right first and it should help some. Just keep an eye on the oil level and limp it along until a rebuild is needed. Unless you have some extra cash laying around then you can have the heads ground and that should fix it as well.
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http://www.correctcraftfan.com/diaries/details.asp?ID=756&sort=&pagenum=1&yrstart=1979&yrend=1979 - 79 nautique
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