new motor questions

[ksny1000]

my max rpms have gone from 6100 to 5600 after breakin period- everything is the same same load same fuel level. its a df200apx

[BigDfromTN]

Does the boat stay in the water? What kind of boat and where is it kept? Can you give any other data?

[Moonlighter]

If nothing else has changed, probably a throttle linkage has moved or slipped and you are not getting full throttle.

[ksny1000]

it is the digital motor with no cables drive by wire. it is a 21 mako i keep on a lift in florida i had a 150 optimax before that had a 15 inch prop with 15 pitch. it was actually faster with that motor and what really stumps me is that at most rpms the optimax was faster for example the suzuki at 4000 rpm goes 26 while the optimax was 28

[Moonlighter]

Forget comparing speeds/rpm with the Opti - the engines are geared totally differently and the Suzuki will require a completely different prop to work as it should. You should - and need - to be able to hit about 6100rpm.

If nothing physical has changed on the boat, there is no way that the rpm should have reduced like you say after the engine is run in. If anything, after 100 hours or so, the Suzukis will loosen up and gain a hundred or so rpm. Engine height is also a critical factor in how these engines are set up.

There must be more to tell us about what is happening?? The more info you provide the more likely it is that someone can help.

What prop are you running - make, model, pitch and diameter, number of blades? It may be a moot point anyway because you were able to hit 6100 at WOT with presumably the same prop? Nevertheless it may help to know.

[ksny1000]

thanks- it is a suzuki 16 inch by 20 pitch 3 blade prop. it is the newest version prop that has the bushing that can be changed without a press. after 2 hours we sea trialed with the tech it hit 6100. did not change anything except kept breaking in the motor as suzuki manual said to, burned about 19 gallons of gas - so less weight. took it to full throttle and now 5600 is max rpm. in theory everything the same except fuel weight the boat should have the same max rpm. my question with comparison to opti is that the suzuki runs a 2.5 gear ratio the opti 1.9 so even if it wasnt a 50 hp increase the suzuki should outperform the opti and it doesnt

[ksny1000]

also the opti had a 15 pitched prop and the suzuki has a 20 so just in theory it should be faster at the same rpm despite the gear ratio- unless i am not understanding pitch

[Hoosmatroos]

The same question in two topics. But oke, as I asked in the other topic, did you trim the motor during the full throttle run?

Explained:

[ksny1000]

yes i did thanks. i am stumped as to the performance of the suzuki specifically losing rpms after breakin and if anyone has ever had that experience.

[SukeHP]

Your motor is brand new .. so i am eliminating that it has any electrical or mechanical problems ..
therefor, the only explanation i can think off is that the prop ventilated the first time you tried it and that's why you've got the higher RPM .. best to retest in calm condition and check out the height of the motor (must be correct before start doing anything else) and try trimming at wot in small increments till you ventilate and/or stop gaining speed and only gaining rpm .. if that occurs from 5500 upward .. then you need different prop or maybe cupping the existing one will do .. all depends on your numbers ..
make sure you test at least from 4000 rpm upward every 500 rpm .. logging rpm, GPS speed, mpg .. that will help you move forward with different props. (all that giving the height of your motors are already correct)

[Solarman]

You might also check the basics, less fuel in tank(s), possible trash in main tank(s), fouling fuel flow? Check fuel filters? Just thoughts, that can limit rpms.