Gang (Warning: this one is kind of long! Sorry.) On a short cruise this weekend, I had an occasion to run the engine a good while and observe some weird engine RPM behavior that we had only suspected on our shorter trips. I know that several mentions of problems similar to mine have been posted, but I wanted to get another set of inputs before my co-owner and I start "working" (e.g swearing, sweating, crying) the problem. Here's the data: - 1982 Hunter 27, Yanmar 1GM diesel (7 HP) single cyl. - Three blade prop of unknown pitch and size (I know, I should have this stuff memorized!). - Since we have owned the boat (about 1.5 years) we have never gotten it to go above 3000 rpm under load (in our defense, we didn't know the top end of the engine for quite a while after we owned it! It is supposed to be 3400 RPM, right?) - Starts fine, generally runs fine, nothing extraordinary. It will go to about 2900 RPM max (won't go any more than than 3000) - Sunny, warm Florida day, calm inland waters, not much wind. Boat is loaded normally. - Once under way, under power only, for about a half an hour or so, with no notice or other indications as to why, the RPMs drop fairly quickly to about 2500 and stay there. The throttle lever has not moved, and moving it forward and/or backward (i.e. jiggling it) does not change the RPM. - I leave it alone at the new lower RPM. Still further along, the RPMs drop again to about 2000, and stay there. Again, no lever movement or any input from the cockpit. - After we passed under a bridge, I killed the engine and we sailed for about 1.5 hours until we got to the marina entrance. Started the engine again, no problems starting, and just for fun I put the hammer down. Interestingly, it goes right back up to 2900 RPM with no complaints. - The engine never back fires, coughs, or otherwise gives signs of misfiring (at least to non-engine experts). It never quits completely, and it always goes to idle and stays at idle just fine. So what do you all think might be going on? I have my suspicions, but I am going to withhold those so as not to taint the advice inputs. Thanks in advance. Ron Vanderveer and Tom Hrkach "Dolphin Dancer"
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Harry A.
Mine too
I don't know if this is THE answer or just an answer but, on mine we found the rpm drop was the same time as when we cleared the channel, which happened to be the time we got everything else put away and sail covers off etc. and then turned on the refigerator. The extra load pulled the engine rpm down. Are you turning on some piece of equipment that is putting a load on the system? Now part two, when we first bought the boat 6 years ago the top rpm was 3300 all day long. Now it will only do 3000 to 2900 with a clean bottom, clean prop and shaft. Haven't gotten a good answer on the why we now have an over all drop in rpm.
I don't know if this is THE answer or just an answer but, on mine we found the rpm drop was the same time as when we cleared the channel, which happened to be the time we got everything else put away and sail covers off etc. and then turned on the refigerator. The extra load pulled the engine rpm down. Are you turning on some piece of equipment that is putting a load on the system? Now part two, when we first bought the boat 6 years ago the top rpm was 3300 all day long. Now it will only do 3000 to 2900 with a clean bottom, clean prop and shaft. Haven't gotten a good answer on the why we now have an over all drop in rpm.
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Ron Vanderveer
To Harry's Point...
Harry (and readers) We aren't really turning anything on that I can think of that would load up the alternator or engine. But your second thought is interesting and might support the idea of a clogged cooling system, which I have seen suggested in the archives. Brent Headberg replaced his mixing elbow with good results. Thanks for the input. Let's see what everyone else has to say? Ron
Harry (and readers) We aren't really turning anything on that I can think of that would load up the alternator or engine. But your second thought is interesting and might support the idea of a clogged cooling system, which I have seen suggested in the archives. Brent Headberg replaced his mixing elbow with good results. Thanks for the input. Let's see what everyone else has to say? Ron
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Bill O'Donovan
Filters perhaps, or crud in the tank bottom
If it were the mixing elbow, you'd be dead in the water because it tends to block up tight like a heart attack. If you replace the filters every season, the other problem may be the intake in the bottom of the tank. No one on earth can access their fuel tank properly, so a fellow last week suggested an ingenious troubleshoot. He puts 2 gallons in a new Tempo tank typically used for outboards. He cuts off the outflow end (to the outboard) and puts it directly to the fuel line at the first filter, completely bypassing the boat tank. If your problem goes away, thank God, because it means the engine is okay and the main tank simply needs to be cleaned out.
If it were the mixing elbow, you'd be dead in the water because it tends to block up tight like a heart attack. If you replace the filters every season, the other problem may be the intake in the bottom of the tank. No one on earth can access their fuel tank properly, so a fellow last week suggested an ingenious troubleshoot. He puts 2 gallons in a new Tempo tank typically used for outboards. He cuts off the outflow end (to the outboard) and puts it directly to the fuel line at the first filter, completely bypassing the boat tank. If your problem goes away, thank God, because it means the engine is okay and the main tank simply needs to be cleaned out.
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Chuck Fort
I had a similar problem
I tried new filters, cleaning the bottm and prop, bleeding the engine...you know all the stuff you are suppose to try. Did not improve. I called the local diesel guy. He replace all the copper washers along the fule path and put in a new injector. It runs like a new engine. Apparently, the old copper washer no longer sealed and sucked air. This lead to trying to use too much throttle, and clogging of the injector. Now it runs great. Good Luck!
I tried new filters, cleaning the bottm and prop, bleeding the engine...you know all the stuff you are suppose to try. Did not improve. I called the local diesel guy. He replace all the copper washers along the fule path and put in a new injector. It runs like a new engine. Apparently, the old copper washer no longer sealed and sucked air. This lead to trying to use too much throttle, and clogging of the injector. Now it runs great. Good Luck!
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Benny
Drop in RPM do not attain Max
You have a frozen throttle cable. The cable is not sliding inside the cover.
You have a frozen throttle cable. The cable is not sliding inside the cover.
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Harry A.
What I have done so far
Over the last two years I have: Removed the fuel tank and cleaned it. It had alot of scum growing in it. Replaced all rubber fuel lines and cleaned all metal ones. Replaced all copper washers. Replaced orginal fuel filter from the fuel tank with a Racor system. Replaced the engine fuel filter (twice) Replaced the air filter Removed, cleaned, greased throttle and fuel shut off cables. And still the engine rpm will not go above 3000. I guess I will remove and disassemble the fuel injector, clean it and put it back in and see if that does anything. Harry Asbury s/v Dolly Phynne
Over the last two years I have: Removed the fuel tank and cleaned it. It had alot of scum growing in it. Replaced all rubber fuel lines and cleaned all metal ones. Replaced all copper washers. Replaced orginal fuel filter from the fuel tank with a Racor system. Replaced the engine fuel filter (twice) Replaced the air filter Removed, cleaned, greased throttle and fuel shut off cables. And still the engine rpm will not go above 3000. I guess I will remove and disassemble the fuel injector, clean it and put it back in and see if that does anything. Harry Asbury s/v Dolly Phynne
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Terry
Ron, obtain the max RPM for your engine...
from your local Yanmar service rep; something around 4200. Warm the engine first then in neutral push the throttle to max. The engine should reach that max RPM. If not, something needs adjusting. If it does, your motor could be over propped, which means you need to have a prop shop make a prop adjustment or change to a two blade. Terry
from your local Yanmar service rep; something around 4200. Warm the engine first then in neutral push the throttle to max. The engine should reach that max RPM. If not, something needs adjusting. If it does, your motor could be over propped, which means you need to have a prop shop make a prop adjustment or change to a two blade. Terry
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