WOT and RPM issues

joshbeye

Cadet
Joined
Sep 2, 2003
Messages
6
Here is one for all you troubleshooters; I have an 89 24ft Century 4500 with a 7.4 Ltr 330HP 454, 8 cyl, Thunderbolt ignition, w/ Bravo 2 stern, 275 hours, not sure the prop size. When we put it in the water this year it ran great, good hole shot, great top end 46-4800RPM 50 mph. <br /> Now for the situation: The boat was stationed at my dock with the cover on before I left for a 5-day vacation. While on vacation, there was about 8 inches of water and some severe storms that came through my area. When I returned home the cover was half off the boat and obvious signs that the water from the storm collected in the loser part of the boat. My auto bilge failed allowing the water level to reach the starter motor. The water level was marked one inch up on the starter motor. This verified the water level wasn’t too high. <br /> Now the problem part: The starter motor would not turn over, the solenoid would click but nothing would crank. First thing, checked oil (it was fine but I replaced it anyway, no water in it), purchased new battery, no crank, removed and dismantled starter motor, (here is where I found the height of the water level, as the rust line in the starter was obvious). I repaired and tested the starter motor (Then later decided to replace it with a new one, didn’t want it to fail while on the water.). reinstalled the starter and hit the ignition. Great news, It started with very little effort! <br /> The motor ran a little rough at idle but when I gave it a little throttle it improved. When I backed of the idle it would run but sound like it wanted to die, more of a fluctuation in rpm’s 400- 700 or so. Occasionally it would die while idling. So rather than take any chances, I did a compression test, everything was good. Replaced the plugs and wires, (did not replace the distributor), and the fuel filter. Ok, now I fired it up and it still ran a little rough for a moment then idled steady at 650 rpm.<br /> We untied the boat and took it out for a spin. From the hole it was a little sluggish, it probably took 5 more seconds to plane and the “punch” didn’t feel like it did the first time out. (The bottom of the boat has some growth but not too much, no hair). The boat seemed to only make 4500 RPM at WOT for about 10 minutes. The speed was probably 40 MPH. I then backed off the throttle to idle and checked the temp on the engine. Temp was fine at the gauge and on the motor it’s self. When I gave the boat throttle this time at WOT my RPM’s only hit 3400 and it took a very long time to plane. (no “punch”) And when it did, the RPM’s only came up to 3700 and the top speed was about 25mph. I backed off the throttle and checked the engine again, it looked and felt fine temp wise. Got back on the Throttle and had the same response. The engine sounded “flat” or “bogged” at WOT <br /> We decided to cruise back to the house (1 mile) and investigate. Our findings were:<br />1. the motor would idle with fluctuation, but it would not die.<br />2. The motor still had good compression.<br />3. The plugs looked OK, and replaced the Coil just in case<br />4. I pulled the distributor cap and noticed some green corrosion on the contacts in the cap. (I cleaned them up)<br />5. Checked all oil –good<br />6. Steering -good<br />7. Trim works – Good<br />8. Checked alternator -Good<br />9. Left it over night, it was late<br /><br />The next morning, we fired up the motor and it did not fluctuate at idle. Thought we had fixed the problem so we went for a spin. The hole shot was still sluggish like before, there was a little “punch” but the motor still sounded “flat” it took about 18 seconds to get the speed to 35mph and the RPM’s were only 4200. We ran like this for about 5 minutes. Stopped to idle –good , Then I checked the motor temp –Good, and gave it throttle again, it only made it to 3600RPM and about 20mph and it took a long time to plane out and slow out of the hole. Now stumped and in need of help…<br /> There is the situation and now I need some outside advice on what to look for/ check next. I have a manual and I feel comfortable working on the engine. Thanks for your help<br />JB
 

JB

Honorary Moderator Emeritus
Joined
Mar 25, 2001
Messages
45,907
Re: WOT and RPM issues

Hi, Josh.<br /><br />You got on the Merc Outboard forum.<br /><br />I will move this to I/O and Inboards for you.<br /><br />Good luck. :)
 

Skinsk

Petty Officer 2nd Class
Joined
Aug 31, 2003
Messages
128
Re: WOT and RPM issues

Spin off your Water seperating fuel filter mounted on the front of the moter, and pour it into a clean bucket. Look to see if the fuel separates out into two layers, like salad dressing. If it does, you have water in your fuel. This could very well be causing all your simptoms.<br /><br />And if the motor is fuel injected, and/or has an electric fuel pump, make sure you fill the filter with fuel again before installing it on the motor. If you don't you will run the electric fuel pump dry for a few secs, and maybe damage it.<br /><br />Scott.
 

Northern Eclipse

Senior Chief Petty Officer
Joined
Jun 24, 2003
Messages
665
Re: WOT and RPM issues

Are you sure you got all the water out of the boat, Like my Wellcraft some boats tend to allow water to move forward when sitting idle, so when I inspect the bilge it may appear mostly dry, but once you start moving the water will slowly flow back, thus adding weight to the back and bogging you down, water in the fuel will also slow you down.
 

joshbeye

Cadet
Joined
Sep 2, 2003
Messages
6
Re: WOT and RPM issues

Skinsk,<br /> I will check the filter on Saturday morning and post the findings. Thanks!<br /><br />Northern Eclipse,<br /> I have noticed there were two compartments in this boat, one for the gas tank which I had to manually pump out... and the one under the motor. The Bilge pump cleared that one out the day I got back from vacation. Ever sense then they have both been relatively dry.<br /> Thanks for the info!
 

K Hultgre

Petty Officer 1st Class
Joined
Jul 28, 2003
Messages
306
Re: WOT and RPM issues

I also agree with SKINSK, it is very possible you have water in the gas. Depending on the amount of gas in the tank I would add a bottle or two of "Heat" this helps remove water from the gas instead of draining the tank. One thing water will do is seep into any opening. Check your wiring if there are any connections that could have been below the waterline the wire could be corroding from inside the insulation causing a drop in current. Performing a voltage check sometimes will not identify the problem (voltage is only potential, current does the work)(had a car that had 12v at the coil but until I replaced the wire it would not start). Also after you ran the boat up to temp the first time then docked it and the next day it ran better suggests to me that the heat from the engine is helping dry things out. Then when you brought it up to temp again the water condensed into a vapor again and caused more problems. I would replace the dist. cap and rotor but allow some time for any condensation to evaporate from the base of the distributor placing a trouble light (60W bulb)next to the dist. with cap off (dont let it rest on any wires or hoses) will help speed up the evaporation. Good luck.
 

kenimpzoom

Rear Admiral
Joined
Jul 13, 2002
Messages
4,807
Re: WOT and RPM issues

If no water in fuel, check all your spark plug wires and spark plugs. Also run a timing light on all cylinder while it is bogging to make sure all 8 are getting fire.<br /><br />Ken
 

joshbeye

Cadet
Joined
Sep 2, 2003
Messages
6
Re: WOT and RPM issues

First of all, I want to say Thanks Guys! After removing the Fuel filter this is what I found in the bottom;<br /> http://www.empirewebs.com/josh/images/boatissue/gas.htm <br />You guessed it, bad gas. I pumped it all out (parts cleaner now)20 gal. I had about half an inch of water in the tank and the fuel looked a little yellow. Never-the-less, changed the plugs<br />and wires and checked the carbs. Everything is back to normal now!<br />Thanks again!
 

andrewgroup

Petty Officer 2nd Class
Joined
Aug 23, 2003
Messages
115
Re: WOT and RPM issues

Is this a steel or poly gas tank? If this is a steel tank, it's highly likely that rust has begun to form ion the inside of the tank and once this starts it doesn't stop. Whenever the rusting areas are above gas, the moisture further creates rust and all of this will end up in your fuel filter. I would recommend you consider getting a replacement Poly or Aluminum tank if this is the case...
 

joshbeye

Cadet
Joined
Sep 2, 2003
Messages
6
Re: WOT and RPM issues

believe it or not, this is an aluminum gas tank. The previous owner had the original one replaced due to the rusting issue.
 
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