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Old 01-06-2011, 05:28 PM   #1
dive4bugz
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Weird Issue

I have an inboard that runs fine for about an hour or so, then it stalls out as if starved for gas. When cold, it starts perfectly. The filter is not clogged, fuel pump is working, and when I work the throttle itll start again but cranks awhile. 351W, 4-bbl Holley, temp oil pressure all fine. I also pulled a couple spark plugs to check for fouling... nothing. Any ideas? Id hate to tear the carb apart if thats not the problem.
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Old 01-06-2011, 06:02 PM   #2
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Re: Weird Issue

If your fuel tank isn't venting it can act like that. It creates a vacuum in the tank and cannot pump the fuel anywhere. When it's acting up, you could take the fill cap off and see if it changes.
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Old 01-07-2011, 08:24 AM   #3
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Re: Weird Issue

I thought about that but I have twin and the port engine is fine. They both feed off the same fuel pickup that splits into a "Y" for each engine. If the tank wasnt venting it would cause both engines to act the same way.
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Old 01-07-2011, 10:03 AM   #4
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Re: Weird Issue

Probably, but not necessarily at exactly the same time. Fuel pumps vary internally a bit so if one is a bit less tight it'd choke first.
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Old 01-07-2011, 12:20 PM   #5
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Re: Weird Issue

Interesting thought. But the port engine will run as long as I need it to... itll idle for hours on end, while Im struggling with the starboard. I would think if it was a venting issue the starboard would quit fairly close in time to when the port did. Im going to check the vent anyways to be sure, and possibly backflush the starboard fuel line. Maybe theres a restriction or partial blockage somewhere that is causing the carb bowls to fill slower than they drain when running.
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Old 01-07-2011, 01:25 PM   #6
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Re: Weird Issue

When one quits the fuel feed requirement through the rest of the system drops to half of what it was when both were running.

Be careful when using "logic" to troubleshoot unless you have evaluated all your base assumptions thoroughly. One slightly wrong assumption can cost weeks in skull sweat and lots of $ chasing the wrong thing until you correct the erroneous assumption. This is especially true when chasing an "intermittent" problem. I could tell you horror stories of chasing those in large industrial hydraulic power systems. Occam's razor applies.
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Old 01-07-2011, 01:36 PM   #7
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Re: Weird Issue

I'm not a mechanic, but had a similar issue a few years back. After weeks, turned out to be a loose ground wire which would intermittently cause one of the fuel pumps to fail in one of the engines. Intermittent b/c at idle the connection was not under any stress, at load, the vibration caused the ground to fail - sometimes. Worth a shot to look at...
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Old 01-07-2011, 02:23 PM   #8
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Re: Weird Issue

I will certainly check that!! I do have mechanical fuel pumps, which I believe pump as long as the engine runs but Its a good idea. Thx!!
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Old 01-07-2011, 08:34 PM   #9
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Re: Weird Issue

good luck, mate. first post, hope it can be helpful to you.
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Old 01-07-2011, 09:26 PM   #10
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Re: Weird Issue

Be careful when using "logic" to troubleshoot unless you have evaluated all your base assumptions thoroughly. One slightly wrong assumption can cost weeks in skull sweat and lots of $ chasing the wrong thing until you correct the erroneous assumption. This is especially true when chasing an "intermittent" problem. I could tell you horror stories of chasing those in large industrial hydraulic power systems. Occam's razor applies.[/quote]


this is very true...i'm an electric/mechanic tech for electric industrial trucks and lifts... my everyday job consists of troubleshooting hydraulic and electrical issues, I wish I could be of more help ... but boats are not my field ...check all plugs related to fuel pump and fuel intake... sometimes the pins on the plugs are not doing proper contact creating this intermitent issues... it has happened to me a zillion times!! good luck!!
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Old 01-08-2011, 09:17 AM   #11
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Re: Weird Issue

An easy way to eliminate the carb question is to swap the carbs from one engine to the other. If the problem follows the carb, then you know what to do (replace the Holley with a Marine Edelbrock aka Carter AFB ). If the problem doesn't follow the carb, then you've eliminated one possibility. That's one of the the beauties of having two side-by-side engines exhibiting different issues

edit: I joked about replacing the Holley, but eliminated a lot of issues when I did just that on one of my older boats.
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Old 01-08-2011, 10:29 PM   #12
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Re: Weird Issue

Might also want to check the pick up screen in the tank to make sure its not clogged but the carb swapping sounds like a good place to start!
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Old 01-08-2011, 10:34 PM   #13
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Re: Weird Issue

Had a problem that sounds similar. Ended up being a bad coil that would short out when it got warm, and would fire right back up when it cooled off. Only took a zillion hours to locate the bugger, and 15 mins to fix it!

Good Luck
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Old 01-08-2011, 11:25 PM   #14
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Exclamation Re: Weird Issue

Quote:
Originally Posted by 'o Cino View Post
Had a problem that sounds similar. Ended up being a bad coil that would short out when it got warm, and would fire right back up when it cooled off. Only took a zillion hours to locate the bugger, and 15 mins to fix it!

Good Luck
Definitely check what o' Cino said and this:

Years ago I had a friend with a boat with a single V-8 inboard. And it did the same thing your one engine is doing. It turned out he had a whole set of bad spark plugs that only failed when they got hot! The only way he found out was by changing everything he could think of, one thing at a time. Changing the plugs fixed the problem.

Good luck and let us know....................
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Old 01-09-2011, 01:03 AM   #15
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Re: Weird Issue

I'm with o'cino too, if it's not fuel, I would think it's ignition. A coil or ignition module would be the most likely but any ignition components could do it if bad enough. The good thing is that you have all your known good parts on your other engine.
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