Pro xs slowing down over time

[haus9393]

Serial number 2B125899

it normal to have your engine slow down over use. In 2016 my 250 pro xs could run a 25 fury 6k rpm and a 26 fury 5900 rpm and run around 78mph all the time. 2017 with 400 hours it was still good running about the same. 2018 with 550 hours it hit 78 mph 1 time when the boat was empty of tackle. The rest of the year I could barely turn 5900 with my 25 fury and high 5700 with my 26 fury. 76 mph was top speed and about 73-75 normal. I do all the maintenance myself and I even sent my 25 fury out for B&B to make up the rpm thinking it might be the prop. Got the prop back and could run 75 by myself around 5900 rpm still. I can raise my plate and loose speed but gain the rpm back. Last summer I got a new lower unit around 620 hours because my original started leaking at the seals. Figured that might be part of it but I don’t think so. Started running stage 2 mercury quickclean in my engine this year thinking it might be due to carbon build up. 2019 I have only ran 75 mph 1 time this year and on average my 25 fury is turning 5800 rpm and my 26 is running 5600 rpm. The engine now has 749 hours on it. Is it just wearing out over time? If that is even a thing? I haven’t had compression tested ever. My tackle load is the same now as 2016. On average I’m running 73 mph by myself maybe 74.5 with barely any gas. 71.5-72mph with 2 people. I used to run 76 with 2 people. I’ve basically lost 200rpm since I got it but it really started showing the decrease from id say hour 550 and on and like I mentioned previously I saw no difference between hours 0-400. I haven’t heard of this really happening to anyone else but then again no one I know has more than 300 hours on their engine. I asked a mercury tech at the service yard last year thinking he would know better than anyone about it and he said they shouldn’t loose speed over time. He said to look at the boat itself but nothing has changed except I added an ultrex which weighs like 20lbs more than a fortrex. I also run lithium batteries now which don’t have much affect on a phoenix but still the boat is lighter now than ever before in the back. The hull has some rubbing scratches on it from the bunks but that’s it. Just want to hear some thoughts.

[Tylerl92]

Ive noticed the same with my boat. I used to run 76-77 consistanly and now 72-74 max. 360 hrs on the motor.

[Savage]

Ultrex killed your speed. Your not the only person to lose a couple of MPH, after adding the Ultrex. Are your RPM readings coming from a Smartcraft instrument?

[haus9393]

Yes rpm is on a sc1000 smart craft gauge. I watch it quite frequently. This evening I ran with 30 gallons of gas around 72.5 mph with my 26 fury. 5580-5620 rpm. These props are mint condition too.

[lpugh]

Time to send your fuel rails to Don for inspection and calibration...….and then 87 octane top tier leading brand of fuel, quickleeen in every tank, 4 oz of premium plus for every 10 galls of gas and use the DFI oil for best results
Check the compression and plugs first, replace the filter and inspect all fuel lines, bulb and pulse pump
Ultrex is probably causing some loss. I may be wrong but I think it is more than 20 lbs heavier

[angle iron]

How much trim does that rig require?
http://www.bbcboards.net/showthread.php?t=518644

[haus9393]

A lot of trim to get the high end performance. I feel it pop up on pad but not like it used to but also it might just be because it used to really pop up only above 75 mph. I’ll check the striker plate tomorrow. I just had my entire trim and tilt replaced under warranty this April. I’ve never checked to see if that area was worn. If my trim is limited then I could see it slowing me down pretty bad because I’m not getting the proper bow lift that a Phoenix requires.

[haus9393]

[haus9393]

[haus9393]

Honestly I never even thought about anything like this. I just felt like I might need to shim the motor to get more trim but these look pretty worn to me. They have an extremely noticeable pit in them probably a few mm thick. Maybe this is why I’m not throwing a massive thick rooster tail like I used to.

[Savage]

Strikers are worn, but if you do a WOT run without the Ultrex, you will find your lost speed.

[haus9393]

I’ll take your word for it since mine takes about 2 hours to remove and install again because I have a through bolted precision bracket over the pedal. I’ve noticed the lost speed when I first put the ultrex on 2 winters ago and I actually asked a similar question after that and other ultrex users said the same. I think they said it weighs 18lbs more than a fortrex and 18lbs on the nose is like 100 in the back supposedly. But I’ve lost quite a bit more since then. I’ll gladly loose 3mph of speed in order to keep that ultrex!!!

[nojretlas]

When did you put the big graphs on and what did you come from?
I lost some speed when I went to (3) HDS 12s on the boat?

[haus9393]

I’ve had 3 big screens since I got the boat. I guess I originally only had 1 12” up front and now I have 2 so add another 10lbs there.

[Fishysam]

any weight on the bow is a lot more weight than just what it weighs. its on the long end of the lever

[Savage]

any weight on the bow is a lot more weight than just what it weighs. its on the long end of the lever

Precisely!

[haus9393]

So possibly the addition of an ultrex at 18lbs more and an extra graph at 10lbs. I think the day last year I ran 78mph I had no graphs on the bow at all because I was about to bring my boat to the dealer and wanted to run it before I dropped it off to make sure nothing else was bad other than my lower unit seals. I know the equation of weight from tip of boat compared to rear. Something like 5-1. Is it safe to say that a motor doesn’t slow down and loose rpm over time??? Or is that a possibility as well? That’s really what my main concern was. I guess one of these days I’ll take my graphs off and take out all my tackle and see what it does just for my own sanity. Probably get new striker plates as well since they look cheap and easy to replace.

[Jtreed99]

It is safe to say that if an engine slows down over time something has changed. Could be compression loss from wear, throttle linkages, injectors, etc. but all things being equal and less performance something had to change. This is difficult to monitor because we are constantly buying more tackle and batteries and bolting things to the boat. Also we tend to remember maximum speeds and forget that we ran that in October or March and now we are comparing that run to a run in 95 degree 95% humidity in June.

[angle iron]

Have you checked your hot foot?

[nojretlas]

Oh and as someone mentioned I would check linkages...my butterfly was not opening all the way because of I would assume a stretched cable.