When the boat is under a load (2001 38 foot Catalina, Yanmar 40hp 3JH3BE), I can only go 3 knots at 2100 RPM's at full throttle. If in neutral, I can easily get over 3500 RPM's. I've replaced the fuel filters and the exhaust mixing elbow, but neither of these fixes worked. When I first purchased the boat, I was able to get 3500 RPM's and 7 knots under load. Does anyone have an idea as to what the problem(s) could be?
Low RPM's under load
- Thread starter Dan9014
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Low RPM'd
Dan, I don't know the age of your Yanmar, but I had a similar problem with a 1980 Yanmar 2Qm15. My remedy was to remove the fuel injectors and have them rebuilt, about $90 each. What a difference! On my boat it was a pretty straight forward job and to me well worth the cost. Wish you luck and good sailing!
Dan, I don't know the age of your Yanmar, but I had a similar problem with a 1980 Yanmar 2Qm15. My remedy was to remove the fuel injectors and have them rebuilt, about $90 each. What a difference! On my boat it was a pretty straight forward job and to me well worth the cost. Wish you luck and good sailing!
I know this is obvious but
I know this is obvious but is the bottom and propeller clean? All the best, Robert Gainer
I know this is obvious but is the bottom and propeller clean? All the best, Robert Gainer
Check the Prop
Barnacles on the prop or a line wrapped around the shaft. I lost almost half my speed due to a few large barnacles. A dirty bottom can increase the load on the engine also. Air filters!!! I'd check the easy stuff first.
Barnacles on the prop or a line wrapped around the shaft. I lost almost half my speed due to a few large barnacles. A dirty bottom can increase the load on the engine also. Air filters!!! I'd check the easy stuff first.
Low RPM
After Katrina my boat sat for a year without moving. First time I tried to take it out, under power it would only make about a knot of headway at full throttle. Had a massive growth of barnacles on the prop. Cleaned them off and all was fine. I would look at the prop first. Barnacles, maybe some rope or fishing line tangled up on it. That would be the first thing to do. Then go from there.
After Katrina my boat sat for a year without moving. First time I tried to take it out, under power it would only make about a knot of headway at full throttle. Had a massive growth of barnacles on the prop. Cleaned them off and all was fine. I would look at the prop first. Barnacles, maybe some rope or fishing line tangled up on it. That would be the first thing to do. Then go from there.
Fouled prop
Look at your exhaust. If your getting black smoke or if you have a sooty residue on the hull you more than likely have a fouled prop. If your prop is like mine it does not take much to drop 2 knots. The fact that your rpm's are reduced that much makes it sound like Rich may have the right answer.
Look at your exhaust. If your getting black smoke or if you have a sooty residue on the hull you more than likely have a fouled prop. If your prop is like mine it does not take much to drop 2 knots. The fact that your rpm's are reduced that much makes it sound like Rich may have the right answer.
Next
Not a lot of choices here. If your sure your fuel is good (no water or other mung) and the flow unrestricted (coming from the filters to the enjectors free and easy) and the exhaust side isn't creating any back pressure then the next thing is to have the injectors tested, ahhhhh. Sorry.
Not a lot of choices here. If your sure your fuel is good (no water or other mung) and the flow unrestricted (coming from the filters to the enjectors free and easy) and the exhaust side isn't creating any back pressure then the next thing is to have the injectors tested, ahhhhh. Sorry.
And then!
Dan, All previous advice is good - but if the engine does not come up to speed - and heaven knows yours is far from its normal speed, I would expect to find the fuel flow restricted in some way. Assuming the fuel pumps are okay there could still be a blockage. You don't say which boat it is but my H376 came with a strainer on the end of the pickup tube in the tank. I got diesel bug and this blocked. Though I changed both normal filters the problem persisted and I eventually removed the tube from the tank and discovered the filter. In a fit of pique I took the filter off. All was well until I got the next dose of the bug two years later. This time the entire fuel line choked and had to be blown out with an air line. It even choked the right angle bend into the Racor filter. Since then I have always used "Fuel Set" - religiously!
Dan, All previous advice is good - but if the engine does not come up to speed - and heaven knows yours is far from its normal speed, I would expect to find the fuel flow restricted in some way. Assuming the fuel pumps are okay there could still be a blockage. You don't say which boat it is but my H376 came with a strainer on the end of the pickup tube in the tank. I got diesel bug and this blocked. Though I changed both normal filters the problem persisted and I eventually removed the tube from the tank and discovered the filter. In a fit of pique I took the filter off. All was well until I got the next dose of the bug two years later. This time the entire fuel line choked and had to be blown out with an air line. It even choked the right angle bend into the Racor filter. Since then I have always used "Fuel Set" - religiously!
Look below the belt
The boat is a 2001 Catalina 38 foot with a Yanmar 39hp (3JH3BE). I guess it's time for me to get out the wetsuit and take a look below the waterline. If the prop looks clean, I'll double check the fuel hoses for any blockage and as a last resort I'll change the injectors. Thanks to all for your help. I'll let you know the outcome.
The boat is a 2001 Catalina 38 foot with a Yanmar 39hp (3JH3BE). I guess it's time for me to get out the wetsuit and take a look below the waterline. If the prop looks clean, I'll double check the fuel hoses for any blockage and as a last resort I'll change the injectors. Thanks to all for your help. I'll let you know the outcome.
Injector Test
You don't necessarily need to change the injectors you can have them tested to determine if one went bad. If you remove them yourself and take them for testing be careful to insure now dirt gets into the injectors or the cylinders.
You don't necessarily need to change the injectors you can have them tested to determine if one went bad. If you remove them yourself and take them for testing be careful to insure now dirt gets into the injectors or the cylinders.
Check the fuel lines, too
We started losing power under load and determined it was restricted fuel flow. Checked everything, including the fuel pickup screen, and turned out the (very poorly routed) fuel lines were being pinched after the tank had shifted slightly. Harry Bethesda, MD Hunter 456 - "Czech Mate"
We started losing power under load and determined it was restricted fuel flow. Checked everything, including the fuel pickup screen, and turned out the (very poorly routed) fuel lines were being pinched after the tank had shifted slightly. Harry Bethesda, MD Hunter 456 - "Czech Mate"
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