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2014 Q25 low max RPM and speed

Potomacbassin’ said:
At first glance, not a prop issue.

I can turn a 17p with my F250 and get 5800 RPM. Hell with a 19p prop I could turn 5500 RPM.

To have such low RPM it's either an engine or fueling issue, and perhaps even a hull/toon issue. I would start with the visual inspection stuff first - making sure you have clean toons. I lost 17mph just recently due to crud covered bottoms. Then are your toons sitting unusually low in the water? Making sloshing sounds when on the trailer? Water in the toons will definitely put load on that engine and prop.

Check all of your maintenance items. Could be a fueling/filter issue but maybe electrical as well (plugs?). Honestly it could be many things so I would always start with the easy items then get progressively more involved. Also the F250 is a very popular outboard so consider posting on other boards such as the Hull Truth can also help in your diagnosis.

Good luck!
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I would agree with this statement. There isn't a prop change in the world that's gonna net you from 4300 RPM's to 5800 rpms. Its only 200-300 rpm's per inch of pitch either way. Mounting holes on transom might gain you another 100 rpm for every hole up, but there is a tradeoff on speed / blowing out in turns.

Something else is here at play. As other suggested, clogged fuel filters / fuel water separator (if equipped), water in toon's etc. Do you know when the last time the spark plugs have been changed? If the previous owner never ran any carbon guard etc, the top of your pistons could be full of carbon and causing lack of power etc.
 
Potomacbassin’ said:
I have the prop lock, and that's the problem! They use a sprung washer (Belleville washer is the official name) that locks the nut instead of a cotter pin. But if the washer fails for any reason the nut can start backing out. I'm still not sure how it happened and need to figure out a solution before I end up donating $800 to the river Gods.
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Are you talking about the washer on the right? This is my Mcgard prop lock.Screenshot_20240706-075419.png
 
Thanks everyone for the feedback! Quick update: Propgods was closed last week so didn't do anything with the prop yet. I did look at the toons as suggested and there was some marine growth on them. There were some small barnacles up to 5mm in diameter. I softened them up with barnacle buster, pressure washed the toons and then took the boat to the sandbar so i could get the entire undersurface and took a scraper to the toons. This improved my top speed 7mph from ~24mph to ~31mph. RPMs increased as well from 4300 to 4600. While I was under there I did notice that I was wrong and I do in fact have a splash guard running the full length of the toons. No water in the toons that I can tell. I do still think I have another issue and am going to look at sparkplugs and fuel filters when I have some time in the next week or two before moving on to prop if that doesn't solve it.
 
While you are checking , check the water fuel separator .
 
Will do, planning to do both water fuel separator and fuel filter at the same time since I have to prime anyways after. Thinking I'll throw in spark plugs at the same time too. The engine just had 100 hour service right before it was delivered to me, so theoretically this was all just done. Possibly something was skipped or done incorrectly, so probably worth looking.
 
Do you know who performed the service , previous owner or dealer ?
If a dealer ,they should be able to tell you what was done .
 
I just reread your original post , the motor has 400 hours now . There are other intervals of required service . Has the impeller ever been changed , is it running hot ?
 
Dealer did the most recent service, I'll check with them what they did. I believe it was dealer serviced prior to that as well. I'm not sure if the impeller has been changed. The engine temp is running perfectly normal
 
I think I've got the boat running a lot better and wanted to update you all. It seems like the problem was multifactorial. I had mentioned in my previous post that cleaning the marine growth from the toons increased my speed from 24mph@4300rpm to 31mph@4600rpm. I looked carefully at my fuel and electrical systems correcting issues and taking it on test runs to determine improvement. I discovered I had a one bad battery and this was reducing voltage to the engine, replacing increased to 32mph@4800rpm. I replaced the fuel water separator filter and fuel filter and they were clearly both brand new and no performance improvement was seen. I double checked all of the dealerships work and it looks like they did everything they should have in the 100 hour service except spark plugs. They said they replaced the spark plugs but they were clearly 100-200 hours old when I looked at them. With new spark plugs that I properly gapped I noticed a big performance improvement immediately, and combined with trimming the motor better (about 1/3 up) I was able to get to 37mph@5100rpm. I am still getting a little cavitation in turns so there may still be some room for improvement. However, I'm feeling pretty good about where it is performing right now and am not going to be in a rush to get better than this. I might look into a new prop to see if that helps a bit. I'm also thinking about a hydrofoil plate for the anticavitation plate such as the se sport 300 to reduce cavitation with turns like when pulling tubes; anyone have any experience with this?

tldr: My problems were primarily a combination of marine growth on the tubes, bad 12v battery, old spark plugs, and improper trimming of the motor
 
Thanks for the update! If you're maxing out at 5100rpm you definitely should re-prop if for any other reason than to get into Yamaha's recommended WOT rpm range for longevity. Many of us run the Enertia prop and it pairs very nicely with our boats, but since yours is a heavier Q model you might want to stick to a SWS2 prop and just pitch down.
 
Q25 said:
I think I've got the boat running a lot better and wanted to update you all. It seems like the problem was multifactorial. I had mentioned in my previous post that cleaning the marine growth from the toons increased my speed from 24mph@4300rpm to 31mph@4600rpm. I looked carefully at my fuel and electrical systems correcting issues and taking it on test runs to determine improvement. I discovered I had a one bad battery and this was reducing voltage to the engine, replacing increased to 32mph@4800rpm. I replaced the fuel water separator filter and fuel filter and they were clearly both brand new and no performance improvement was seen. I double checked all of the dealerships work and it looks like they did everything they should have in the 100 hour service except spark plugs. They said they replaced the spark plugs but they were clearly 100-200 hours old when I looked at them. With new spark plugs that I properly gapped I noticed a big performance improvement immediately, and combined with trimming the motor better (about 1/3 up) I was able to get to 37mph@5100rpm. I am still getting a little cavitation in turns so there may still be some room for improvement. However, I'm feeling pretty good about where it is performing right now and am not going to be in a rush to get better than this. I might look into a new prop to see if that helps a bit. I'm also thinking about a hydrofoil plate for the anticavitation plate such as the se sport 300 to reduce cavitation with turns like when pulling tubes; anyone have any experience with this?

tldr: My problems were primarily a combination of marine growth on the tubes, bad 12v battery, old spark plugs, and improper trimming of the motor
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good info, thanks! and a reminder that I need to check my plugs... ;)

also, it's normal to need to trim down when turning (especially when doing watersports) with a toon. that was something i had to learn, lol...
 
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