Looking for some advice. Both engines on my 41 have lost RPMs. No load we are getting around 2845 and under load somewhere around 2400. The problem started around 2 weeks ago. In the last 2 days we have done a full tune up, Tested the fuel for water (with negative results) and rebuilt both racors and replaced the filters "TWICE." The injectors where replaced a few months back. We also replaced both air filters.
Bottom needs to be cleaned hual it out. Also if the bottom needs to be painted check out the new paint by sherman williams we put it on no more problems this summer. Check the old messages for proper paint.
never worked on a 41' but if they have turbos/supercharged they may be giving you a problem, or the air filters. or if you can do a falling ball test on the oil compaired to new oil, that will tell you a lot, too thick: piston blowby, injector not seated just right, there are many things. fuel oil dilution, there are several things for that too. good luck.
Speaking from experience I would say your no load speed is pretty good. I was at boat forces center, and have seen a 41 lose 150 RPM's with just a light flim of slim on the hull. Even more when you have a hole in the Skeg. I would be interested in hearing your final findings of what caused your slow full load run. Might even suggest double checking your throttle linkage for full throw.
Hey man I work at boat forces and run into these problems on a daily bases, I agree with everything that has been posted so far. Your no load sounds fine it should be around 2850 if it is higher than that you got lucky with the fuel pumps on there. To check the skeg without pulling it slowly take the cap off and listen for air, of course if you get a steady hissing you probably have a hole. The bottom job usually is the cuprit, but another thing we ran into earlier this year was a bad batch of fuel filters they were 2 micron instead of the 10 micron. Another thing you can check is the scupper valve's to the tanks sometimes if the screens fall of bugs build nest's and what not in there and clogg them up. If you need anymore help give us a hollar at boat forces we have seen just about anything and can offer up plenty of advice.
We have pulled the boat and cleaned the hull. I was not there when that happened but the MK3 that went said there was no hole in the skeg and that there was not much growth on the hull. Returning from the haul-out they got 2575 on one engine and 2550. However now the oil pump on the port engine went out so we are replacing that then we will try and get the RPM's back up. Thanks for all the info and ideas so far.
Since 903's are usually relatively easy to troubleshoot, I'd recommend keeping in mind what you originally started with; a simultaneous loss of power on both engines, so before tearing into one or the other, look at what's common between both mains- fuel. I'd seriously consider what's already been said about either a bad shipment of fuel or possibly the wrong micron rating on the filters.
Were these RPM's achieved using throttle control or someone physically pushing on the governor linkage. Unless its changed the erector set used to hold the throttle cable was always loose or sideways causing the throttle cable not to pull the lever all the way forward.
Hey, we just went through the smae thing here in Ft. Myers Bch... If your props are slightly bent in any way, the RPM'S will drop and then one engine will rob rpm's from the other to even out. We did a no load test, all was well, we pulled the boat out and cleaned the bottom, still no speed, when we started examining the props, we found that the stbd prop was off a little... That was it!! Good Luck
