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Old 29-11-2009, 12:45   #1
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Erratic RPM

I pulled out this morning to head for Florida from Charleston but didn't escape the marina.
I installed a new 30 micron primary filter last week. The system had an old Lucas water separator but no filter in it. After bleeding the system I got it started and ran it for half an hour at the dock. It ran well. After I pulled out I noticed that the rpm would slowly cycle up and down 5-10%. 1200 RPM to 1100 to 1200 every few seconds. I headed to the main dock and the engine quit as I approached. No damage done but I'm stuck until I get a mechanic tomorrow...unless...
Could the erratic rpm be due to a loose hose connection allowing air into the system. Or could it be because the system is straining to draw fuel through the new 30 micron filter?
I'm suspicious of two things I did.
1. My advisor/helper struggled reconnecting one of the fuel lines onto the secondary filter. I was concerned that it may be cross threaded.
2. To install the Racor primary I cut the copper lines and put tight fitting diesel rubber fuel line over it, using a pair of hose clamps to secure each end.
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Old 29-11-2009, 13:26   #2
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could well bve air in the system, check out everything you touched Air would be mt bet
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Old 29-11-2009, 16:19   #3
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I am betting that this is a Perkins?
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Old 29-11-2009, 16:48   #4
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Quote:
Originally Posted by Chief Engineer View Post
I am betting that this is a Perkins?
Good bet me thinks!

I'd also bet there's air in the system. Maybe as a result of the filter being too dense, but not likely. Try bleeding it again. And when testing the engine afterwards, tie the boat to the dock real good and run it in gear to put some load on the engine.

/Hampus
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Old 30-11-2009, 04:58   #5
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The Chief is right, a Perkins. Bleeding it is a nasty, tedious job. Before I do it I want to find the problem. Most likely it's an air leak either from the type of connection I used at the new filter or a cross threaded fitting. I called a mechanic to come and look at it this morning. I need some peace of mind or I'll scrub my trip.
Thanks for the input.
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Old 01-12-2009, 18:08   #6
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If you still have the original secondary filters on the engine, a common area for a leak is right where the fuel line comes from the primary filter. The Brits call them olives, I call them o-rings that are on the tubing going into the filter.

Go over all your connections......air, (I call them Champagne Bubbles) will get in to any poorly secured/damaged connection.

If you do not have a return line to the tank....these bubbles will accumulate in the secondary filter.

Finally....if you installed a Racor...make sure the "in" sides is from the tank....and the "out" side to the engine.

Don't axe me how I know this....it is embarassing.
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Old 02-12-2009, 06:27   #7
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Thanks Chief.
I chased down the marina's most renowned diesel expert. He came over and bled the system again. What he said is that Perkins are the worst for bleeding because they are so unforgiving of champagne bubbles, as you called them. We got it started, ran under load for an hour and then he loaded me up with knowledge. We made seven hours down the ditch without a hitch.
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Old 03-12-2009, 20:10   #8
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"down the ditch without a hitch" has a nice ring to it......
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Old 03-12-2009, 21:45   #9
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Congratulations! Isn't that a wonderful feeling. Had the same problem with my 4-107 many years ago and had a friend over that bled it correctly. From then on I really learned how to do it properly but the moment it started after he bled the engine I was ecstatic and willing to buy him two cases of Bud instead of the one that he agreed to originally.
regards,
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