YSM 12 Problem

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Rick

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Oct 5, 2004
1,095
Hunter 420 Passage San Diego
Frustrated and could use some help. Rebuilt my YSM 12 over the winter. Everything is new or overhauled from the fuel tank to the exhaust out the stern. After running at 3000RPM's for about 20 minutes out the harbour my power drops to around 2500 and further drops to the point I get nervous and shut down the engine and let it set for about half an hour. We seem to be able to continue at about half throttle and head back to dockside without incident. The 1979 Hunter 30 has a 3 bladed prop which the boat came with. A club member seems to thick that there is too much oil in the engine and it's getting splashed up into the piston cylinder after the engine gets hot and the oil expands and the engine is over working itself. The oil level is at the full mark but he expresses concern that it is to much because the engine is slated aft on it's motor mounts. The oil gets black real quick but no grit in it. The YSM manual states that the oil capacity is 3/1. Any ideas as to what the 1 means? Anyone else experience similar problems? Upsetting after dumping $2000 in new parts!!!
 
F

FP

Throttle creep

You may need a clamp on your throttle cable to keep it from creeping down. MRS044386 CABLE BRAKE by Morse or UFLL14 Cable clamp block, Fits 3300 & 33c cables by UFLEX USA
 

Rick

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Oct 5, 2004
1,095
Hunter 420 Passage San Diego
Not obvious things

Throttle was hand held in place. That's the frustrating part, the boat was recently launched and the fuel, filters and entire system has less than 3 hours on it. Works perfect for less than 30 minutes and begins to act up but no alarms. Received an email that thought maybe I'm trying to drive a three bladed prop to hard(over 2700 RPM) with a 12HP motor. Any thoughts?????
 
Jun 6, 2006
6,990
currently boatless wishing Harrington Harbor North, MD
Well the "1" is probably an "L"

for liters. As for the RPM loss it can't be intake or exhaust restriction as that is all new. How about the flapper valve at the hull exhaust port. Is it opening all the way. Also try reducing power for a few minutes and then go to full throttle. Does she go back to 3000 RPM? Assuming all the above are OK I'm thinking fuel starvation. Did you replace the fuel tank? Could be the maintenance knocked loose some junk and your new filters are clogging or the new lines are "coming clean" of metal/rubber bits that occur during installation. A piece could be lodged in a pump valve and causing a slight "back leak" through it. It could be a slight kink in the supply line also. Just enough to restrict the flow at full throttle. Did you put anything new in the supply line like a check valve? I've worked on fuel systems for some time now and one thing is for sure: Cleanliness is next to Godliness and both are required for success. With the pressures and flow rates in these systems way down (low side pressure not injector pressures) and the tolerances nothing less than 0.0000 it does not take much dirt/metal shaving/rubber bit to foul up the works. Roosa Family TRITIUM
 
Jun 6, 2006
6,990
currently boatless wishing Harrington Harbor North, MD
The 1 could also mean

3 in the sump and 1 in the filter. Chcek your manual for total capacity. If it is 4 qt(liters) then I'd say sump + filter. If it is 3 then it probably means "L" for liters.
 

Rick

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Oct 5, 2004
1,095
Hunter 420 Passage San Diego
All New

Thanks for your input Bill and great care was taken in cleanliness. Tank, lines, filter units and filters all new. There is no flapper valve at the stern however the exhaust thru-hull is under the stern end. The harbour has been quite calm the three times we went out and it didn't seem to be obstructed. We're going to trial it tomorrow and keep the throttle arounder 2500 and see if it craps out. I'm thinking maybe the suggestion that the 3 blade prop is to much for the engine???? I bought the boat in Maryland and had it trucked up and have not seen it run prior to this.
 
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