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351w surges when accelerating |
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Plan B 
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Joined: April-23-2013 Location: Clearwater, FL Status: Offline Points: 48 |
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 Topic: 351w surges when acceleratingPosted: December-24-2014 at 10:57am |
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Trying to get to the bottom of an issue, feeling defeated and thought some extra minds might help resolve the problem.
Problem: Boat runs well at idle and top end, however when accelerating the motor surges and it's never a clean transition. Also, there is a knocking noise that only occurs under a load at higher RPM's that we have yet to locate. What we have: RH 351w New Mallory electronic distributor (MALYLM554DV) New Quick Fuel M-650 Marine Carburetor Newly installed lifters (thought the old ones may have been sticking) We have tested for and have: good compression on all cylinders, oil pressure (fresh oil), fuel pressure (fresh gas), vacuum leaks, good plugs, new plug wires, and timing is within spec. The firing order is a bit unclear, the consensus and best working order we have tested is 18456273. Any help would be appreciated. Thanks,Ryan. |
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backfoot100
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Joined: January-03-2007 Location: United States Status: Offline Points: 1897 |
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Posted: December-24-2014 at 11:34am |
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Ryan,
You put that QFT carb on around august of '13 or there about. You had said that it ran awesome after that. Is the acceleration issue something new? When was the dizzy changed out? What was the last thing that you did when you noticed the problem? The knock could be any number of things. Does it sound like something on the top end (valve train related) or something deeper like crank or cam related? As much info you can provide would be nice. |
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When people run down to the lake to see what's making that noise, you've succeeded.
Eddie |
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TRBenj
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Joined: June-29-2005 Location: NWCT Status: Offline Points: 21113 |
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Posted: December-24-2014 at 12:17pm |
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Id like to know what "timing within spec" means to you.
Spark plugs are new? |
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Plan B
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Joined: April-23-2013 Location: Clearwater, FL Status: Offline Points: 48 |
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Posted: December-24-2014 at 12:49pm |
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We replaced the dizzy along with the QFT and it did run much better. We decided to grab that dizzy after burning up numerous pertronix ignitors and coils. We later discovered that an arching coil wire may have been culprit the entire time.
The top end is not running perfect it's running about 90%. To emphasize on the sound, its not just a ticking... sounds like the valve train is coming apart. Its coming from the top of the engine all around. We recently replaced the exhaust hose, but other than that she has just been sitting without use for a few months. |
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JPASS
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Joined: June-17-2013 Location: Orlando Status: Offline Points: 2283 |
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Posted: December-24-2014 at 1:00pm |
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Have you checked your valve clearance at the rockers being that you just replaced the lifters? Could that be the cause of the knocking you're hearing??
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'92 Correctcraft Ski Nautique
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Plan B
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Joined: April-23-2013 Location: Clearwater, FL Status: Offline Points: 48 |
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Posted: December-24-2014 at 1:20pm |
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Yes,clearance has been tested and to spec. The rockers are non adjustable, torqued on to spec and we tested for clearance before the lifters pumped up.
Typically you will hear out of spec rockers tapping at idle there is no noise at all until we did about 2000 rpm. |
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81nautique
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Joined: September-03-2005 Location: Big Rock, Il Status: Offline Points: 5768 |
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Posted: December-24-2014 at 1:31pm |
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Pull the valve covers and check to see if there is excessive play on the rockers. You replaced lifters so you may have ground a lifter or the cam down if the motor wasn't broken in properly upon restart, if there is excessive play that could be your source of your top end rattle.
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TRBenj
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Joined: June-29-2005 Location: NWCT Status: Offline Points: 21113 |
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Posted: December-24-2014 at 1:43pm |
Total timing may be off as well- "ticking" may be detonation= bad, bad bad. Can you answer my question? It also sounds like you used the improper procedure to verify lifter preload... What does "in spec" mean to you? |
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Plan B
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Joined: April-23-2013 Location: Clearwater, FL Status: Offline Points: 48 |
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Posted: December-24-2014 at 2:12pm |
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Sorry TRB,I overlooked you post... Timing is 10 degrees base timing per engine manual and total timing of 32 degrees. Spark plugs were replaced a few months back and look good.
81nautique: there is no play in any of the rockers. |
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Plan B
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Posted: December-29-2014 at 3:22pm |
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Turns out it was just a fuel filter issue..coming back to the boat after a few months the old filter was leaking so we replaced it. Put no thought into that being the cause of the problem. Put another filter on, surge and noise went away. Funny how it can be something so simple that makes you think it's something so serious.
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TRBenj wrote: