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Old 07-03-2016, 03:12 PM   #1
Lt. JG
 
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Default Revs are hunting

Hi all

I have a 2000 5.0 carbed v8 which is fully serviced every year and this year had a complete carb rebuild. I've had no problems this year at all but today had a new phenomenon I'd like to understand.

We cruised at 3400 rpm for about half an hour then eased back and idled for about three minutes. I pushed back up to 3400 but the engine was hunting a bit. Surging up and down by about 100 rpm with no change to the throttle. I went up to 3800 and the issue cleared and when I dropped back to 3400 through to about 2800 the problem was there.

I ran back in at 3800 with no problem and at 1400 down to idle revs the boat was fine. I didn't get a chance to retry it as the weather changed.

Any advice gratefully received

PH
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Old 07-04-2016, 02:57 AM   #2
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While the tach was not steady in these rpms could you feel and hear the engine power change as well?

Just wondering if it's a tach issue.
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Old 07-04-2016, 11:39 AM   #3
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i could definitely feel it hunting and see it on the tach.
im sure it is fuel starvation and will investigate;

fuel pick up blockages
air vent bvlockage
fuel pump

do you think this is the right area?
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Old 07-04-2016, 12:13 PM   #4
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I would think if fuel starvation the higher the rpm to worse it would be but you started that at 3800 all was well. Not sure why this would be true for a fuel or electrical issue.

You're just going to have to start checking things out.
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Old 07-04-2016, 12:22 PM   #5
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My thoughts exactly! my last boat had a 225 opti outboard and that had a similar thing but didn't clear at higher revs. Turned out to be a blocked fuel pick up pipe
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Old 07-11-2016, 07:10 AM   #6
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It was really windy with us this weekend but I cleaned the screen on the bottom of the fuel pick up, removing some muck, and i didn't have any symptoms. I'm not saying the problem is fixed - but I didn't have any symptoms.
The wind meant that runs were short though so I'll find out next time hopefully!
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Old 07-11-2016, 11:08 AM   #7
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Hopefully it's fixed, however if there is muck on the pick up there may be more in the tank and rough seas will stir it up. You may need to have the tank cleaned.
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