Suzuki 2020 DF250S alarm over 5000 rpm

[Keith1969]

I have a 2020 Bentley tritoon with a DF250S motor, when rpm hits 5000 a alarm sounds and motor gores into safe mode, 21 pitch stainless prop, I have had cavitation issues on other boats and do not believe that is the issue, any idea what maybe going on here? Specs on motor indicate 5300 to 6300 rpms and I can get no where near that without alarm sounding....Thanks for any advice!!

[Moonlighter]

Alarms are often done as codes eg a series of beeps.

Also depending on what gauges you have, there will usually be an indication on the gauge lights (eg a particular light will come on) or the digital gauges (if fitted) will report a speciiic fault.

Can you throw any light on any of that?

Failing that, all fault/alarm codes are logged in the ecu, and your Suzuki mechanic will be able to plug their laptop in and use the Suzuki Diagnostic software to interrogate the system and find the details, and will be able to work out how to solve the issue from there.

[Keith1969]

Ok thank you!! The tilt warning comes on on C10 unit, but alarm on Simrad says engine rev limit raised, however I do not see a surge in rpms or hear it like have had on other boats with caviation issues!! Motor starts visually shaking when it goes into limp or safe mode.

[Moonlighter]

It sounds very much like the over-rev protection may be being activated.

These new engines protection systems are quite sophisticated and the over-rev protection kicks in very quickly. the computer cuts spark advance and fuel supply and the engine will then run badly, its like a race car that has the pit lane rpm limiter activated, it kicks and farts etc - does that sound familiar??

From memory, when it happens, if you slow down, put the throttle back into neutral with the engine running and wait a couple of seconds, the alarm will clear and you will be able to accelerate away again.

If you test this procedure and that is what happens, then you can be pretty sure that the problem is the prop losing grip on the water.

Then you can investigate the cause - it can be the wrong size or type of Prop is fitted (eg too small diameter - the Suzukis typically run a larger diameter prop than other manufacturers) or the engine is set too high or trimmed out too far.

Its something that your Suzuki mechanic or boat dealer should be able to help with. The 250’s and 300’s typically run a 16” diameter prop, if you run less than that you can get issues with props losing grip.

I really cant add very much more because I have no experience with props on pontoon style boats.

Having said that, a VERY useful resource is Suzuki USA website and if you look there, they have some performance tests with various different boats - eg I found this example for you where they have a pontoon boat that is set up running a 250 with a 3 blade 16” x 20” prop. That may give you some ideas that could help with your setup.

http://www.suzukimarine.com/Product%...2585%20DF250TX


Other boat tests for the 250 can be found here:

http://www.suzukimarine.com/Product%...012/DF250.aspx

Hope this info helps.

[Keith1969]

The prop is a 9571-150-21 Lexor stainless, I wonder if I need to move to a 16 with 20pitch prop?

[Moonlighter]

Well, that Lexor appears to be a 15” dia prop, correct?

Possibly thats the problem or at least part of it. From discussions I have read, it seems that pontoon style boats need props with high thrust and, that means extra blade area. several manufacturers even make props with large blade areas and lower rake specifically for pontoon style boats.

So the 16” would certainly have MUCH greater blade area than the 15”.

Have you tested the over-rev theory as suggested earlier, to see if the alarm clears when the throttle is brought back down for a second or two?

I would suggest that you talk to a spe******t prop supplier that knows the requirements for pontoon boats and is also familiar with Suzuki’s. Tell them about the current issues and the prop you currently use, and ask their recommendations.

Are you aware that Suzuki’s, with their offest drive shaft, run a very different gearing to other makes? And that as a result, they need different sized props to the other makes. Eg putting the same size prop on a boat that works for a Yamaha WILL NOT work satisfactorily with a Suzuki.