I am only getting 5100 rpms on my 1999 mercury optimax, but hitting a top speed of 65 mph. I have a 25p Tempest prop. Shouldn't I be getting 5700-5800 rpms?
Should I be concerned about the low RPMs? Also, I have noticed black carbon build up around the inside of the prop. I heard that this is a result of low rpms.
This is my first bass boat, purchased in January, so this stuff is new to me. I have had it out 5 times now.
Any suggestions or comments would be appreciated.
sumthins wrong,, you should be turnin a 25 more that that with that set up
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Do you have a jackplate? If so try to raise it up a bit. But watch your water pressure. If no jackplate maybe try a 24p.
2007 Triton TR20X HP
Mercury Optimax 225 Pro XS
Something seems off, my first guess would be the tachometer.
Yep, I have a 25p Tempest on my R91 and it will turn way more rpm's. Before you start throwing parts at the motor, take it to an authorized Merc dealer and have them take a look at it. Have all the computer updates been done to the motor?
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Is that speed on your GPS or your speedo? I had the same issue with my 520 and my hot foot throttle wasn't hooked up properly to the cable and was only allowing me about 60% throttle, if you have a foot throttle...I would check that out. If your boat is truly running that fast and the tach is that registering that low..your tach is way off. Your boat sounds like its running the speed it should be.
You need to start with the basics, test compression, get good tune up and start with prop 3" below the pad. My first change would be to try a 25 p Trophy (four blade). Your speed 65 mph (if GPS) is close to optimum and I'd think with a Trophy, 69-71 would be your goal with a normal load by your self.
Wouldn't a 4 blade of the same pitch lower the rpms from a 3 blade?Originally Posted by Garfish
Dale Sinclair original
RPM should be around 5800. With a motor of that year my guess it might be a ethanol/gas line issue. or something as simple as your primer bulb collapsing under full throttle. either one would restrict gas flow and the motor would run rich and cause carbon build up inside the prop. this would be a cheap fix that you could do yourself and give you a starting point.
I have the EXACT same boat as you do...motor and everything...Boat came with a 4 blade trophy....that prop sucked for my boat to say the least. I would stay with the prop that you have now, set it 3.5 inches below pad. But if your running 65...i think that you have a problem with your tach. My tach was sticking...all I did was turned the connection on that back. Before you move it make a mark with a marker...then turn it back and forth...make sure you get it back in the same spot, hence the marker.
65mph was reading on my GPS at optimal conditons, but 62-63mph is more regular. I think I will have the tach checked. The prop blades are rough, it does need to be smoothed out. Hopefully these are the issues....No hotfoot, but the throtte feels "loose", meaning I have to keep my hand on it or else it will jump up on me...I do have a jackplate and will have the motor postion checked. Compression is 100-105 on all cylinders, not sure if computer updates have been done.
Previous owner used DFI oil and claimed to used ethanol treatment in the fuel, but the mechanic that checked the engine out prior to purchase said it could use a new fuel line.
Tach is incorrect.
I had a similar issue with my 150. Ended up being a small piece of the lining of my fuel line had come apart due to ethanol and was reducing fuel flow.
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