Poor Hole Shot and only 4200 rpms. Advice?

[Borkman]

Greetings,

I'm a very new 2005 901 CDX owner, and a brand new member of BassBoat Central. I was steered here by a kind member of another board, who told me you guys would be the best for seeking solutions to problems. I am having hole shot issues and problems getting to the desired rpms. Here's a summary of what I have:

Plows water for 7 - 10 seconds to get on plane with my wife and I, total combined weight of 300 lbs (don't ask me to divulge the wife's portion of that total!). If I have a third passenger, I need to have the third buddy crawl up front to help get the bow down. I've been on other bass boats, and haven't observed such a sluggish start from other rigs. I read that the 901 CDX is a heavy hull, and perhaps a bit under-powered even with 200 ponies. I'm running the Tempest 25 pitch, three blade on a 2005 Optimax 200 2-stroke. PVS holes appear to be medium. Once on plane, I get decent top end speed (mid 50's), at least decent enough for a first time bass boat owner, not comfortable getting too crazy!. But I'm only spinning 4200 rpms WOT. Even on calm water and 10 - 12 miles of open water in front of me, I can't get over 4200 rpms even playing with the trim, unless of course I cavitate the motor.

After a bunch of research, here's more that I can offer:

Center of shaft (cone?) is approximately 3" below the pad. From what I read, this should be close to the sweet spot.
I have absolutely zero rooster tail (not that this is important to me). Not sure what this means.
I have no adjustable jack plate. Motor is mounted to a fixed setback bracket, so there's zero adjustability.
Motor has five mounting holes, and is mounted on the second from the top (meaning it's almost as low as it can be).
I had my wife bury the Hot Foot to the floor, and while looking under the cowling, I can confirm that the Hot Foot is set up correctly, and the throttle is indeed buried all of the way. I was hoping for a quick fix. . . . Manually, I couldn't turn the throttle body any more.

I've tried a buddy's High Five 23 point prop. Very good hole shot, approx 4800 rpms WOT, but I dropped 20 mph on the GPS. I tried a few other props last fall that I could bum from friends, but was never able to hit the magic 5700 rpms. I wasn't able to try a 24 pitch prop. And I've subsequently lost my notes on rpms and top end gps speed.

I'm not running a full tank of fuel (< 1/2), and I don't ever have the livewells full. I don't "think" I'm over loaded with tackle, but then does anyone think they have enough? Can't we always use more?

Boat was purchased last year, with only 5.2 hours on it. Motor checked out, i.e. good compression, injectors, etc. Maiden voyage, I observed the issues that I'm having. Now that I'm a bit more comfortable with it, I'd love to get the full performance out of her.

I did check out the Nitro Set-up thread here on BBC, but there was just so much info that I was overwhelmed, and little discussion on problems and issues with the solutions.

Will completely pulling out one or more of the PVS plugs help enough? See above where all three holes are plugged with what I suspect are the medium opening plugs. What about dropping to a 24-pitch prop, either 3-bladed or 4-bladed? Or am I looking at installing a jack plate, either manual or hydraulic? Or are there perhaps some systemic motor issues that I need to investigate?

I sincerely appreciate any advice, Borkman

[shapfromla]

I'm not a Nitro Owner but may be able to help some.

1.) Your prop is too big. I don't know what props are best for your nitro but staying with the same, A 200 on that boat will likely need a 23" tempest or possibly even a 21". But in the mean time, remove all of the PVS plugs from your prop immediately. The temptest should not need them and it is hindering your hole shot.
2.) Verify your tachometer reading. Although possible, 55 mph at 4200 rpms is a little suspect to me. You may have a tachometer that is not accurate so I would have a technician verify that before going too far.
3.) Bottom line is you are dealing with a Big boat that is a little under powered but can still perform well and make you happy but you must prop down to achieve that. I would expect a smaller prop will significantly decrease your hole shot times and possibly get you to around 60ish on the top end.

[Fishysam]

Agree that your 25 pitch is to large, try 23 or 22 or maybe a 21

agree I suspect that your tachometer is giving you false numbers. (My 2015 z8 20'1" with 250 at 3/4 throttle and low on fuel/gear spins 4700 at 55mph with a 25 tempest)

so after addressing those two come hit us up with some more information

also if you have good conditions and no boat wakes you can probably trim the motor all the way to the top of the trim at wide open throttle (it won't go into the tilt section)

[Borkman]

Thanks gents,

I'll call the local Merc dealer on Monday. My guess is they may be two weeks out on appointments. I'll also have them make sure the injectors and power packs all check out. That's what someone else suggested to me here in MN.

However, I'm accustomed to my work boats (I'm a fish biologist here in MN) and I really don't think my Merc is into the 5000 range. A 2-stroke running 5000+ rpms should be much louder than my motor is, at least that is what I'd suspect. Maybe I'm wrong, but the old 2-stroke Merc 50 on my electrofishing boat would just scream WOT.

However, that being said, on the Nitro Set Up thread on this site, most other 901 CDX owners were running the same Tempest Plus 25. I've called around to all of the Duluth / Superior Merc dealers, and no one up here has demo props for this boat. Everything up here centers on walleyes, and Lund is king. A Nitro dealer in Missouri that I called on Friday suggested perhaps a Tempest 23 or a Fury-4 24. Those are non-existent in the demo world here.

I think I'll take the motor in for an inspection. Never considered that the tach may be giving me faulty numbers. I'll just ensure that everything is purring as it should. Then maybe I'll call down to the Twin Cities and see if any of the Tracker dealers down there have demo props for me to test drive.

Now, I'll go out and yank out those PVS plugs and see what happens tomorrow on the lake . . . Thank you!

Borkman

[Mcjenson]

It’s tough without a good local prop shop that lets you swap. My last boat, (tracker 195) took like 6 different props to find something that worked well.

[Fishysam]

My 250 pro xs 2 stroke is really quite to me on the boat, but when another goes by on the lake it's loud as heck.

[Sun Fish]

I had a 08 901 and ran both a 25 and 24 tempest. In the spring and fall the 25 gave me a better top end around 65 but mid summer hole shot suffered so I dropped to the 24 and top end was 62-63. Sounds to me your motors not running right. Both top end and RPMs your reporting dont jive with a healthy 200 on a 901.

[Borkman]

Thanks Sun Fish, you aren't the only one to suggest to me that my motor just isn't right. That's a bummer! I'll be calling and getting her in to see the doctor at the first available appointment. Hopefully it'll be an easy fix.

I'd be plenty fine with 60 mph if my rpms were correct. I'm not out to race anyone out on the lake, but I do want her performing as she was designed to do so.

[remaly181]

To me, your 25p prop seems right for that set up. The thing that interests me is not knowing your exact prop to pad measurement. That is critical. If you are too high or too low then your overall performance will suffer. 3 1/2" is the typical starting point. Another point of interest is not knowing your water pressure at WOT. There are a lot of variables in getting the perfect set up. Unfortunately, it takes more than changing the prop. That 200 should be running around 5800 rpms with your speed in the 60s so long as you have all the variables in line. Also, the tach seems suspect to me as well, but if you are running in the 50s and the motor has the potential for 60s then it may not be that far off. Just know, a lot of us on this board have been running boats for quite a while and we too struggle with setting things up from time to time. It is very hard to diagnose your problem(s) without being there with you. I would suggest focusing on the easier, inexpensive things like prop to pad before racing to the mechanic. Chances are, the motor is just fine considering it only has 5.5 hours on it.

[Sun Fish]

Thanks Sun Fish, you aren't the only one to suggest to me that my motor just isn't right. That's a bummer! I'll be calling and getting her in to see the doctor at the first available appointment. Hopefully it'll be an easy fix.

I'd be plenty fine with 60 mph if my rpms were correct. I'm not out to race anyone out on the lake, but I do want her performing as she was designed to do so.

Its probably something simple like a coil pack having you down a cylinder or something.

[Borkman]

Greetings all,

As suspected, I can't get my motor in to the Merc shop for a check up for two weeks. So I'm doing a few things that I can do:

I'll replace the spark plugs, just in case
I'll replace the fuel filter, just in case
I just pulled one of the PVS plugs in the 25 Tempest Plus

However, when I was under the cowling, I noticed that the motor may be a 2.0 L? Is that possible? I thought the 200 Opti's in 2006 were all 3.0 L. But on the serial number plate, it clearly says:

2006 200L OPTI
Max RPM 5750
HP 200 / KW 147
LB 495 / KG 225

If this is a 2.0 L, am I just expecting too much from this 200? Should I be content with mid-50's gps?

I have an appointment, and have asked the Merc dealer to check compression, spark to all cylinders, I've asked for the computer print out on the diagnostics, and if everything checks out, have them review the accuracy of the Tachometer. Having the tach inspected is 2 hours of labor ($105 / hr) doing a lake run. Is there anything else I need to ask for?

This weekend, I'll take her out and see if the new spark plugs, new fuel filter, and one less PVS plug makes any difference in the world. I do have a buddy with an engine hoist. Is it worth dropping the motor down one set of holes, from 3" below pad to about 3 1/2" below pad, or should I check the other variables first prior to dropping to 3 1/2" below pad?

Again, I sure appreciate all of your time in helping a newbie to bass boats. . . . respectfully, Borkman

[Borkman]

I forgot to mention that I don't know my water pressure, as remaly asked. I never knew what that was for until recent google searches. On saturday, I'll pay more attention and report back once I get my engine checked out at the doctor's shop.

[Fishysam]

My 250 is a 250L, pretty sure the L is a long shaft. 20" (a xL is a 25", a xxL is a 30" motor. )

there may be a little dial behind the tach with 5 positions, many people have had tachs start working correctly again by switching that knob one position and or moving it back.

these are not specifically nitro questions you can definitely start a new conversation on the Mercury forum, just make sure you have your serial number because the guys there will pull up your motor, it's history, Any service memos, recalls....

we have the same gear ratios in the lower units I do not see how it is possible to be running the same prop, my 20'1" boat with a 250 runs max 5900 rpm, your boat with a 200 would need to be at least 600 pounds less weight than mine to string out that prop. Pitch is 25, this in jello would move forward 25" in one rotation. There is a slip calculator on mercury website, 4200rpm and 1.75 gear, and a 25 p at 55mph is a slip of 3%, that's extremely good. Aka I think your tach is off. My 25p 250proxs will touch 76mph on a good day low on fuel at 6000 that is 3% slip paired with 6000rpm

[BMCD]

Pretty sure most ran a 25p tempest or trophy And sometimes a 24p. The L/Us were different back then and they had alot more slip. Its a rear tank design so it will never have great holeshot.

I agree Something is off with the #'s posted. Almost like your down a cylinder, and that is one of the years they had issues with the power packs.

No rooster tail generally means your getting good lift.

[Kerz321]

Borkman,
I would recommend cylinder compression test before going into too much engine work. Cylinder compression will eliminate many possibilities while providing valuable info.
Vic

[Borkman]

Thanks Vic, I'll be asking for that during my Merc dealer appointment in 10 days ... stay tuned!

[Borkman]

I'm back from the doctor's. . . . Merc Opti passed with flying colors! Compression was good. Power to all six cylinders. They said there's nothing wrong with the actual motor. They did tell me that with the old Opti's, you can't just check the tach's rpms like you can with the new 4-stroke Yamahas. So the tach was not verified for accuracy.

New spark plugs and new fuel filter the other day. I did take it out last night to test the plugs and fuel filter. I also removed one of the three PVS plugs in my 25" Tempest. Actually, my hole shot now is acceptable. Much better than ever before, although I only had maybe 15 gallons in the tank. With my wife and I, and not a huge runway to test her out, I did get up to 4700 rpms and 52 mph gps.

I did take note of my water pressure, somewhere north of 12 but not at 15 at WOT. Not sure what this means.

So I guess that leaves me with either:

1) a fawlty tach, but I'm thinking I should still be getting better than 52 mph. Combined, my wife and I weigh in at 300 lbs;
2) Need to demo a 24" prop and see if that helps with rpms and mph;
3) Lower my motor from 3" below pad to 3 1/2". I have one hole to drop down. Merc guy said today that the #2 hole is the typical installation, and that was before he saw that I'm at the #2 hole, or;
4) Invest in a jack plate.\

Again, I'm very grateful for any advice. Thanks!

Borkman

[Borkman]

BMCD,

Can you fill me in on what you mean by getting good lift? I don't know what bow lift is all about, or what is good, bad or otherwise. When I stomp on the hot foot, the bow raises, then drops down when she gets on plane. When I trim her up, last night to 4700 rpms, I didn't really notice the bow lifting at all. I did notice the splash created by the hull moving further back past me and towards the transom.

thanks!

[remaly181]

Now that you know the motor is good to go, it is time to figure out your setup. To me, that prop should be fine. It is the 3" PTP that is most likely giving you fits. There is a lot hydrodynamics involved when you are trying to lift thousands of pounds of solid mass on top of water. The way I understand it is if your prop is not far enough below the pad then you create water flow problems (cavitation) which prevents your prop from gripping properly. You essentially create an air pocket where you should have water flow. Also, when your PTP is too high it limits your torque thus the reason you tilt all the way down when taking off.

[BMCD]

remaly , but that would also create RPMs which he is not seeing. Propshaft 3" below is normal on most boats and acceptable. Borkman, lift is basically as u describe, when u trim the motor up the bow should rise, and u should notice the spray is no longer underneath u. But at 52 i doubt it can get the lift it will at speed. Your speed given to us should be full throttle, and trimmed up as far as she will go.

You just got to eliminate stuff, the tach is the next thing.

Am I reading you have no Jack plate? Then i would agree in dropping it, closer you are to the hull the deeper the motor needs to go.