Max RPM out of 50HP efi is 3400

[benningtonr]

I have a new to me 2004 18' Fisher with a Mercury 50hp EFI 4 stroke. Yesterday was our first outting, i read max rpm is 6000. The most I could get was 3400.
I still need to look at what prop is on it, but I am sure it is the one that came with the motor/boat when new. I got it from my inlaws that have had it since new and he was very particular, the boat and motor are in excellent condition. The boat sat in the garage since Oct with ethynol stabilizer in the gas. It fired up first turn of the key and runs/sounds great. with the exception of the rpm's being low, oh, it also stumbled once after 6-7 min of WOT, It did not die, the rpms just fell off like it was going to, i backed her down and she purred like a kitten at 2000-2500 rmp's for the next two hours of putzing around the river.

 

[Fun Times]

Hi there, welcome to iboats!

Being the first trip out on a new boat to you, did you by chance try raising the power trim/outboard up a few degrees from the lowest position to see if the RPM would go up any higher while underway?

No alarms are sounding at all?

 

[benningtonr]

I did try moving the trim up and down some, there are no alarms. It dings once when I turn the key to the run position, then to the start position it fires right up. no other dings.

Thanks for the welcome, nice to have a group of folks you can bounce questions off of.

 

[flyingscott]

We need the year and serial#. You also need to do a cylinder drop test it sounds like you are not running on all cylinders. Here is why I think that, you are 2600 RPM shy of the max rpm that means you would need to drop 13" in pitch to work that is a big drop. Since I bet you are running about a 15" pitch prop so you would need about a 2" pitch prop. When it's running get a plastic pliers and pull the spark plug wires off 1 at a time if the idle doesn't change that is the cylinder that has the problem. Another option is get a spark checker make sure it jumps a 7/16" gap.

 

[benningtonr]

2004 S/N 1B020095
These are the numbers on the prop
0814A
21301110
TURNINGPOINT (but it looks like ( IURNINGPOIN )

I have raced stock cars for many years, owned and worked on, I was on a Busch team (hard card holder) for a number of years.
If a cylnder was down I would know, right. I can tell when a four cyl is running on three.
I started out in the 80's racing ford 2.3L race engines in mini stock race cars.

I could be wrong though, this is my first time playing with an outboard engine.
My last boat had a 350 and a OMC outboard.

Thanks again for the help, and if I am wrong let me know, I will check for spark.

 

[flyingscott]

Your prop comes up as a 10 7/8" diameter with 11" pitch. Being down a cylinder is my opinion and the easiest to diagnose. After that compression and if all those are good then you are into the fuel injection and the sensors.

 

[Fun Times]

Thanks for the quick reference about your engine mechanical history... As you may know there are many question that pop up on a forum and sometimes it's a little challenging at getting a quick read about the persons level of experience one may have....or not.

Since we're not able to be there next to the engine, all we're really able to do is suggest trying a few things out that would be within reason of a possibility of being wrong and offer up some suggestions of how to go about proceeding with them if it may make it easier/safer on someone. So it's really not going to be a matter of who is right or wrong, it's going to be more about the process of elimination by actually verifying by tests to ensure that area in question (no spark, etc.) really isn't a problem vs non visual guessing as one just may never really know.

Being an EFI marine outboard engine, you may eventually need to get the engine connected to a marine diagnostic scan tool to see the live data to ensure none of the EFI sensor parameters are out of range and verify the tachometer gauge is reading correctly.

Here's a parts catalog for your engine plus a couple of service bulletins that might pertain to your engine,,, http://www.crowleymarine.com/mercury-outboard/6993.cfm?mdl=Q4DJPV&q=1B020095#

Below is some info about your propeller,
TURNING POINT PROPELLERS:
Hustler H1 Prop Diameter 10.875 x 11 pitch RH Propeller part number 21301110 .$82.99
http://boatpropellers.iboats.com/propeller-showcase/turning_point/

 

[benningtonr]

Great info, i will look now, I have a mercury certified service shop just down the street, may be worth the effort of towing her down and getting a look see at the diagnostics.

Thank you fun times, again, every ones help on these forums in invaluable.

 

[benningtonr]

I just talked to the shop and here is what they said:

Drain out 6 month old gas, even though it has ethynol stabilizer
fill with fresh, add 1 quart two stoke engine oil to the fresh 20 gals
Also add the appropriate amount of Quick Clean fuel cleaner

Run it for a few hours, vary the throttle full WOT to slow cruising speed.

He said that it is probably the fuel pump, the oil will lubricate it and the cleaner will clean the rest of the fuel system, lines injectors and etc.....


What do y'all think

 

[jkillion]

I had pretty similar problem last year. Try this. Replace all fuel lines on the engine side, rebuilt the mechanical pump and run off a small external tank (I got a 3 gallon one from bass pro for like 40 bucks). Its about 2 hours of work once you get your parts collected together.

Granted mine is a 200 EFI, but your symptoms are the same as mine were and it was a fuel supply issue (at least for now, still trying to chase down on board fuel tank problems).

 

[benningtonr]

May have to rebuild pump. We took her out Sunday and it was better with the kleener and 2-stroke oil 44-4500 rpm max. Sounds like it was cavitating, it would have spots of the RPM's raising rapidly, only 2-300 but sounded like the prop was unloading, then it would bite again. so i baked her down to 3500 and it was smooth trolling, about 13 mph

 

[benningtonr]

Well it was the fuel line from the take to the motor, rotting from the inside out.