I just bought a 2001 Ranger 520 VX with a 2001 Mercury 225 Opti. Mercury 25P Tempest prop. The previous owner had the lower unit replaced with the same gearing and the motor mount bracket replaced, which the motor would have had to come off of the boat for. He has not had it in the water since the work was done. When we took it to the lake for the lake test, the previous owner was the first to notice something was wrong. He said it should come up on plane faster. The speedo wasn't working, so we had no idea how fast we were going once up on plane. I got a GPS after I bought the boat, and found that it is only running about 55 GPS. We tried the prop off of his new boat which is the same, and I saw a 60 MPH max, but wasn't sure if it because of the conditions at the time,(strong tailwind). I concluded the difference was negligeable for this rig with the tailwind..etc. I wound up with 2 plugs out of the prop to improve the hole shot, but it is still not like it should be, and the previous owner said it was routinely 67-68 and he even saw 70 MPH once or twice with a light load. This boat only has me and my 10 year old son in it with one tackle box that has hardly anything in it. I suspect that they got the motor height wrong when they went back on with it, but they assured him it went back just as it was before. What else could it be? It was running 68 before, and now it's running 55. The prop was worked at the same time but all they did was clean it up as I understand it. Also, as I said we tried his prop with some improvement, but not much. I haven't measured the prop height from the pad yet. Any ideas?

UPDATE: Well, finally got it figured out. I never would have thought the plugs would have been the problem. I suspected once before that it might be missing on one cylinder but brushed that idea aside because the previous owner said it just came out of the shop for a service check, tune up. The plugs were carboned up pretty bad. They put new plugs in it and it jumps out of the hole now. I saw 66 MPH @ 5700 RPM. I think it will do 70 if I can keep my foot in it long enough (I was cramped for space)and I must admit I am a little rusty in driving at these speeds. It was chine walking to the point I had to back out of it a couple times. Glad to have the chine walk, it's just a driving thing, but I wonder if I should put the motor back down one hole where it was. I think before I do anything, I will take it to Steve and let him look at it. I have some opinions on a couple of shops in the area as a result of my experiences with them pertaining to this problem. I am still debating wheather to post my experiences with these 2 shops. I am not quick to bash anybody, but I will seek advice and consider it more and let you all know. Good to have the boat running like it should. Thanks to Steve at Steves Custom Props for his insight and suggestions that helped in tracking down the problem, and thanks to Michael Bristow at North Texas Fiberglass whose troubleshooting led to the fix.

Don't have any ideas......just wonder why you need to go 60 with a ten year old.

Are you trimming the engine up after you get on plane? I know it took my friend 5 years of ownership to figure out that once he gets on plane at full throttle, bang the trim up a few times and he went from 44 to 55.

gclark, I agree with you that rig should definitely run faster I would think mid to upper sixties as the previous owner stated. Unfortunately I don't have any suggestions as to why it is not attaining that speed other than motor height. Were the RPMs in the normal range at WOT for that motor?

Oh yeah I forgot to mention, it is running from 5300 to 5400 rpms. It kinda fluctuates around there. This is on the Merc smartcraft gage. For the poster that wanted to know why I need to run 60 with a 10 year old....He knows how to ride and I know how to drive. 60 is nothing for this boat, or us. With that said, I don't drive that fast all the time, but I want the boat to be able to run like it should. Hope that clears it up for ya.

Are you trimming it up after you get on plane with wot?

I had the same boat, it should run mid to upper 60's all day long .... You need to measure your prop shaft height, in relation to the pad, to see where your motor is first of all then we can begin figuring out what is wrong. Also what were your RPM's at Wide Open Throttle ?

5300 rpms is telling me the motor is about 2 inches too low. You should be able to turn that 25 tempest at 5700.

I agree with the other posters. measure your prop shaft heigth. start at 3 1/2" below pad. that should be about right.

could also be a problem with the current prop. sounds like your boat is plowing the water.

If you ever come to lake fork, stop by and i'll be happy to check out your current setup and take a look at the prop for ya.

I plan on coming to Fork soon. I will hook up with you Steve. I wanted to meet you anyway. I agree the first thing to do is find out where the engine is. The only thing that has changed since the previous owner had it in the water, is the engine came off and the prop work.

How do you know that when the engine came off, it was re-mounted in the same location as before? It sounds purely like an Engine Height problem to me, and that's relatively easily solveable.

Yeah, that is what I am saying. It is about the only thing that makes sense to me. I will check the height tonight, and post what I find. I hope that is all it is.

One other thing to check is how the trim tab was adjusted. I noticed a difference after getting my Yam back from shop and it helped when I put it back to previous setting.

Good Luck

I would also check your throttle linkage. Problems with a sluggish hole shot combined with a low top end speed sounds exactly like the boat isn't seeing full throttle anymore. That would be my first thing to look for. That would be a heck of an easy fix.

Good point Bass Hog. The only reason I haven't done that is because the previous owner said the RPMs are the same as before. But it is easy to do, I will check it anyway. I might get lucky.

Normally top end speed and RPMs go hand in hand. I cannot imagine it running 65 - 70 mph @ 5300 RPMs. In fact I would bet a steak dinner that if Steve put the numbers to it you would not get 65-70 mph even with no prop slip. Also, a lower motor usually gives you a better hole shot. A 10-15 mph drop would tell me that the motor is significantly lower. If you are trimming it i would do as suggested above.