Optimax 225 2001 problem

Hello to all friends
I'm Manolis from Greece and i'm having a problem with the 225 Optimax (300h year 2001).Ii'm having it on inflatable boat (800 kg only the boat but all the weight is about 1.400kgs) with bery deep V (26 on transom). The motor can't hold the rpm between 2200 rpm and 2800rpm. I can' t keep the morot for example at 2.500 rpm. I ask 3 mechanics authorised by mercury in Greece but i have several opinions with no specific cause of this problem (and cost also of course). I tried mirage plus propeller 21" but is the same problem. All the tests in the computer is good with no alarms or any other obvius cause. Note that the motot gives me all the power 5400 rpm 45knots. We have check the sparks, TPI, the compression works just fine, but no luck for me. So i 'm in dead end.
Is it familiar this problem to anyone?
Thanks in advance for your response

Re: Optimax 225 2001 problem

MELAN said:

Hello to all friends
I'm Manolis from Greece and i'm having a problem with the 225 Optimax (300h year 2001).Ii'm having it on inflatable boat (800 kg only the boat but all the weight is about 1.400kgs) with bery deep V (26 on transom). The motor can't hold the rpm between 2200 rpm and 2800rpm. I can' t keep the morot for example at 2.500 rpm. I ask 3 mechanics authorised by mercury in Greece but i have several opinions with no specific cause of this problem (and cost also of course). I tried mirage plus propeller 21" but is the same problem. All the tests in the computer is good with no alarms or any other obvius cause. Note that the motot gives me all the power 5400 rpm 45knots. We have check the sparks, TPI, the compression works just fine, but no luck for me. So i 'm in dead end.
Is it familiar this problem to anyone?
Thanks in advance for your response

Click to expand...

Check the hub in your prop be sure it is not spun and doesn't need replacement your dealer can do this or try a different prop same pitch.

Re: Optimax 225 2001 problem

Thanks for the response
I have all ready doing that. I change the propeller with mirage plus 19" (same pitch with the old one) but the problem still.
Any other idea for the cause??

Re: Optimax 225 2001 problem

Hi Elan,
Hey, your ESL is better than a lot of friends I have that claim English as their mother tongue.

What is the boat doing at the problem rpm's. I ask that because there is a particular speed in any planing boat where it is trying to climb on plane, but collapsing back into the hole. It is like trying to drive up a steep hill. With a truck you shift gears. Boats don't have gears, so you must either go faster or slower.
Weight distribution in the boat, engine mounting and trim angle, and hull aids, such as trim tabs can help.
Another idea is that a propeller that has exhaust relief holes would slip enough at that speed to allow the engine to get into the power (speed) band. One that would have the bite you need and the relief is a high five.
It also helps to prop the engine so WOT is right at the top of the allowable engine rpms.

hope it helps
John

Re: Optimax 225 2001 problem

More information.

With a 1.87 LU, the numbers you provided do not compute. (negative prop slip) I do not know your LU gear ratio for sure.

I also don't know the max rpm spec for your engine, but I suspect it is higher than 5400.

It would be good to have your tachometer calculation checked.

It is 8:30 am here. I will check back after noon.

John

Re: Optimax 225 2001 problem

I?m glad that you interest because I?m in dead end right know and some friends told me that some mechanic in US probably find the solution. I?m still hope for that!!
I?m increasing progressively the throttle and up to the 2100rpm the engine corresponds regularly. I continue increasing the throttle to the 3000rpm+ but engine does not correspond (I?m not seeing the rpm counter increase rpm while increasing the throttle and has exceed enough for 3.200 rpm). Suddenly abruptly engine got 3000 rpm (the clue in the counter it exceeds the 3500). I feel the boost of engine and I hear it also. In the progressive rise of throttle between 2100 until the boost engine is not heard rising rpm?s or to tries goes up and it cannot, also the boat it does not goes with stern up. After I got 30knots and progressively begin to cut speed and rpms near to 3.000 rpm with 20 knots I stop lowering the throttle to keep the speed close to 14 knots but engine continues losses rpms and speed and is stabilized to 2100rpms and less than 10 knots.
The engine is heard work irreproachably from 0-2100 and from 3000 and above up to 5400. Also the boat has trim tabs lenco and the manufacturer told me that the smaller speed is about 14 knots with this machine.
I made all the test (change hub) and propeller mirage 19 pitch but the problem persists. The rpms is in the range of mercury.

Best Regards

Re: Optimax 225 2001 problem

Melan,
What you are describing may very well be simply be a propeller issue. If you can track down some information, we can help you. Assuming 1.87:1 lower unit gear ratio, your speed and rpm numbers are impossible.

I suspect your motor is simply overloaded. You may be trying to operate it at an rpm and torque it cannot support.

1. Verify your tachometer.
2. Verify and report your LU gear ratio.
3. Verify your speed with GPS.
4. Verify and report the max rpm specification for your engine.

Then maybe we can figure this out.

hope it helps
John

Re: Optimax 225 2001 problem

Ratio is 1.75.1 on 3.0 liter 225 Opti's the 2.5 liter 150 Opti's are 1.87.1 and rpm spec's are 5000-5750rpm's. The early Optis's are very picky about voltage and if you have a lot of assy's and voltage falls below 12.3-12.5 engine will not run right at low speeds. Mercury recomend's a minium of a 1000MCA battery for this engine. Also has the air and fuel pressure been checked? If off it will run like crap at low speeds and pressure need to be exactly 10 psi difference. As old as the engine is I would replace the fuel pump diaphram(#21-857005A1) to ensure proper fuel supply to vapor separator. The next item would be the diaphram(#17) in diagram(#804533) this diaphram is in a regulator that balances air and fuel pressure, especially important at low speed operation. Also check the spark plug wires as these are known for burning into at the tips, this may explain your "boost" or the fuel /air pressure injector/s are not getting a good connection due to corroded connections on them from salt water usage. The prop calculator works with the correct ratio= 3000 rpms with 19 prop at about 6 percent slip, I also suggest you try the 3 blade Torrent prop or the 4 blade Typhoon to help hold bow down at slow speeds

Re: Optimax 225 2001 problem

Thanks all the friends for the help.
Finally after meany tries the TPI is damaged and i change it. The volt in TPI is less than the regular at low rpms (for 2000rpm we see 2,04 but after the replacement we get 2,45)
Also i step down the engine one hole (in 2nd) and with mirage plus 17" i get 42kn at 5500rpm.
I wish to all more fun with your boats at the sea, and remember the best way to past the winter is to boating.