For the last few months I have been experiencing a "stumbling" of my 1GM10 Yanmar at startup. It starts okay but idles rough, will not take any throttle advance, and emits black smoke. After 10 minutes or more of idle and/or several sessions of attempting to increase RPM with no load, it will rev up and it then is "good to go". It then seems to have as much power, or more, than ever. (I just did a bottom job, cutlass bearing, and one motor mount.) I did have to disconnect the exhaust hose and muffler, to replace the motor mount, and in the process discovered and replaced bad hose clamps (maybe leaking). I am now wondering if cooling water, (which previously leaked out), is standing in the exhaust system and causing back pressure. My exhaust hose rises almost to the top of the lazerette before exiting at the waterline. That is a head of at least 2 to 3 feet that the cooling water must be forced up and over. It seems quite a bit of exhaust pressure would be needed to accomplish this. I realize that the raised loop will prevent water from flowing back to flood the engine and boat, but does anybody else have this high of a loop in their exhaust hose? Any other thoughts?
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Black smoke is your key here.
Don: When we see black smoke it usually indicates a fuel loading problem. This can be caused by several different things. 1. prop pitch 2. dirty bottom 3. bad injector/s etc. etc. I would not think that the rise in the loop would have caused any problems here. If it works fine after blowing out the fuel in the system, this doesn't make a lot of sense (to me). When you shut down your engine, you need to let it cool down after running for about 5 min at 1000rpm. Then rev it to the rated RPM (3000 or so) and shut it down by pulling the fuel shut off lever. This prevents the fuel from draining down into your crank case and clears out the cylinder too.
Don: When we see black smoke it usually indicates a fuel loading problem. This can be caused by several different things. 1. prop pitch 2. dirty bottom 3. bad injector/s etc. etc. I would not think that the rise in the loop would have caused any problems here. If it works fine after blowing out the fuel in the system, this doesn't make a lot of sense (to me). When you shut down your engine, you need to let it cool down after running for about 5 min at 1000rpm. Then rev it to the rated RPM (3000 or so) and shut it down by pulling the fuel shut off lever. This prevents the fuel from draining down into your crank case and clears out the cylinder too.
D
Don McCoy
Agree
I agree that black smoke is unburned fuel but since it occurs when the tranny is dissengaged, both power train and bad bottom are eliminated. Coking of the mixing elbow and a plugged intake filter should show up at high RPMs and load. I would think that a failing injector would also show indications at times other than just startup. I have considered that possibility and not anxious to pull and have it tested until I eliminate anything that I may have done to the exhaust hose and muffler. I removed them, and then replaced hose clamps when I replaced a motor mount. That seems to be the time the trouble started. I have ALWAYS been puzzled by the exhaust sytem. The muffler seems to be a 6" OD X 1' plastic pipe with an inlet and outlet in the center of a cap on each end. There are two penciled arrows on one side, pointing at each end with an oval drawn between them. This is the only marks and I have no idea what baffles etc. are inside and if it makes any difference which side is up. Past inquiries have suggested that it must be a prototype of some sort. Does anyone else have their exhaust hose loop all the way up to the top of cockpit seat and then to the water level through hull? This approximate three foot rise would seem to me to take quite a bit of exhaust pressure to force the cooling water up and out. If this loop is an anti-siphon measure, there should be a vacumn break somewhere and I am wondering if I may have eliminated an accidental one by the new hose clamps. Standing water in the exhaust system COULD explain my troubles. I would like to know more of others systems. Help
I agree that black smoke is unburned fuel but since it occurs when the tranny is dissengaged, both power train and bad bottom are eliminated. Coking of the mixing elbow and a plugged intake filter should show up at high RPMs and load. I would think that a failing injector would also show indications at times other than just startup. I have considered that possibility and not anxious to pull and have it tested until I eliminate anything that I may have done to the exhaust hose and muffler. I removed them, and then replaced hose clamps when I replaced a motor mount. That seems to be the time the trouble started. I have ALWAYS been puzzled by the exhaust sytem. The muffler seems to be a 6" OD X 1' plastic pipe with an inlet and outlet in the center of a cap on each end. There are two penciled arrows on one side, pointing at each end with an oval drawn between them. This is the only marks and I have no idea what baffles etc. are inside and if it makes any difference which side is up. Past inquiries have suggested that it must be a prototype of some sort. Does anyone else have their exhaust hose loop all the way up to the top of cockpit seat and then to the water level through hull? This approximate three foot rise would seem to me to take quite a bit of exhaust pressure to force the cooling water up and out. If this loop is an anti-siphon measure, there should be a vacumn break somewhere and I am wondering if I may have eliminated an accidental one by the new hose clamps. Standing water in the exhaust system COULD explain my troubles. I would like to know more of others systems. Help
Anti-siphon
Don: Our 2GM20F has an anti-siphon between the heat exchanger and mixing elbow. I cannot imagine how the loop would cause this type of problem. The exhaust is powerful enough to push all the water out of the muffler. I would check out the mixing elbow, but would have to agree that it does not sound like your problem. It seems to me that your injector is the most likely problem here. Check with the Yanmar shop about a rebuilt vs. a new injector. It is quite easy to remove the injector. I think that they can test it for your too.
Don: Our 2GM20F has an anti-siphon between the heat exchanger and mixing elbow. I cannot imagine how the loop would cause this type of problem. The exhaust is powerful enough to push all the water out of the muffler. I would check out the mixing elbow, but would have to agree that it does not sound like your problem. It seems to me that your injector is the most likely problem here. Check with the Yanmar shop about a rebuilt vs. a new injector. It is quite easy to remove the injector. I think that they can test it for your too.
J
John
Loop
I have a 25.5 with a 1GM10 and also have a "hose loop" identical to yours. Since mine has not been altered since the boat was built, I am certain the exhaust hose path is an original installation feature. I have had no problems I believe are related to the exhaust system.
I have a 25.5 with a 1GM10 and also have a "hose loop" identical to yours. Since mine has not been altered since the boat was built, I am certain the exhaust hose path is an original installation feature. I have had no problems I believe are related to the exhaust system.
D
Dan
Also have loop
My loop also goes up to the top of the lazarette. I have had fuel problems lately that have caused some similar conditions to what you describe. I would check the bottom of your fuel tank first, then filters, and finally the injector which is pretty easy to get to and remove. I am going to empty my tank for cleaning soon and a local shop suggested that I remove the screen at the fuel pickup in the tank if it is still there as that could also be part of my problem. I have a primer bulb in my fuel line before the first filter to aid in bleeding the fuel system. When my engine is running rough and down on power a squeeze of the bulb seems to correct it for a few seconds. I hope this helps.
My loop also goes up to the top of the lazarette. I have had fuel problems lately that have caused some similar conditions to what you describe. I would check the bottom of your fuel tank first, then filters, and finally the injector which is pretty easy to get to and remove. I am going to empty my tank for cleaning soon and a local shop suggested that I remove the screen at the fuel pickup in the tank if it is still there as that could also be part of my problem. I have a primer bulb in my fuel line before the first filter to aid in bleeding the fuel system. When my engine is running rough and down on power a squeeze of the bulb seems to correct it for a few seconds. I hope this helps.
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