RPM's on a 200 mercury

mkeleher

Seaman
Joined
Feb 18, 2012
Messages
58
Gentlemen,

How many RPM's should a 200 mercury turn? I'm no mechanic by no means but surely an outboard motor on a high performance boat will turn at lease 5500 easy. Here's the deal, I took my motor to a local "out of his house" mechanic because my motor at WOT would only turn 4000 RPM's with a 25p tempest plus. He tells me I have good spark and compression on all cylinders but that the pitch is too big for this motor and that I need a 23pitch. I listen to him since he is the machanic and get a 23 pitch. Now I only turn 4500 RPM's. I tell him it still wont turn any more than 4500 so he says, bring it back and I'll work on it. One week later he changes out the throttle postioning sensor, 2 injectors, and installs a idle stabalizer. He then tells me 4500 is the best this motor will do and that nothing is wrong with it, oh and that I now owe him 791$. WHAT!!!!!! The motor runs exactly how it ran when I took it to him the first place. I know I need a new mechanic, but what RPM's should I be running and what else could it be? Its a 1991 mercury 2.4 200 Electronic fuel injected on a 19 ft norris craft. The boat will only go 50 with this motor on it. Norris craft tells me the boat was made to go 70 + with a 200 merc. Help please.........
 

wired247

Lieutenant Commander
Joined
Oct 8, 2011
Messages
1,557
Re: RPM's on a 200 mercury

It should go 70+ MPH and the 25 pitch should work fine. He put the idle stabilizer back on? Throw that piece of crap in the garbage or at least disconnect it. What are the compression numbers? What did he set total timing at? It should be 23 BTDC unless you have heavily cut heads. You think he'd at least give you numbers for your $800.

FWIW injectors almost never go bad. You can send them in for cleaning to a few different places for $25 a pop and they come back like new. My 2.0 fat block 150 turns a 21 pitch prop 6000 RPM. It will twist a 17 pitch 6800. I'm building a 2.5 liter 200 EFI right now to be a 7000 RPM motor.

Find out what the compression numbers are even if you have to do it yourself. A healthy 200 EFI should be in the 120-125 range. Disconnect that stupid idle controller and the rev limiter if you have one, disconnect the knock sensor. Keep the oil injection if you must. Its good to 6K most of the time. Get a good analog meter and a DVA meter to go with it. Look up the CDI troubleshooting guide.

4500 is cruising speed.
 
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oldman570

Lieutenant Commander
Joined
Mar 25, 2011
Messages
1,615
Re: RPM's on a 200 mercury

When you dropped to the 23P prop the RPM went up 500, so if you were to drop to a 21P prop you should get close to another 500 RPM gain. This would put you close to the 5000 RPM that is on the low side of the recommended RPM range. If this is the case then you were over pitched on the prop or the boat has a overload and can not push the weight. Best to take the boat to a scale and weigh it and see if that is the trouble. Several prop websites have prop calculators that will give a good insight as to just what the setup will run as it sets. JMO
Oldman570
 

wired247

Lieutenant Commander
Joined
Oct 8, 2011
Messages
1,557
Re: RPM's on a 200 mercury

Its not a 125 HP 3 cylinder. Its a 2.4 chrome bore 200 EFI on a 19 foot bass boat. It should be going 70 mph+ in the high 5000's to low 6000's. If its not, theres something wrong either in tune, setup of the boat or with a component of the ignition or the injection or with the motor itself.
 

1nebel0

Chief Petty Officer
Joined
Nov 28, 2005
Messages
512
Re: RPM's on a 200 mercury

I spin all my 200's 6,000 all day long.. I subscribe Wired....
 

mkeleher

Seaman
Joined
Feb 18, 2012
Messages
58
Re: RPM's on a 200 mercury

Compression is 120 on all cylinders with spark on all of them. I found someone to trade me a 23 tempest for a 25 tempest which is what I originally had so at least I dont lose out on the prop. The motor is VERY doggy out of the hole like I am pulling a skier. Could the switch boxes be breaking down causing the stator to fail? A guy I work with said he has heard of switchboxes failing at higher speeds. When I put the new stator and volt reg on it was charging the battery fine when I ran the motor.
 
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Faztbullet

Supreme Mariner
Joined
Mar 2, 2008
Messages
15,616
Re: RPM's on a 200 mercury

Did you ever figure out if you had 2.5 ECU on the 2.4 as it wont run as it to fat due to mapping in ECU.....What the part number on ECU? Did you test/set TPS?
 

mkeleher

Seaman
Joined
Feb 18, 2012
Messages
58
Re: RPM's on a 200 mercury

It has a 2.4 ecu. The mechanic put a new tps on it and that didnt change anything.
 

Faztbullet

Supreme Mariner
Joined
Mar 2, 2008
Messages
15,616
Re: RPM's on a 200 mercury

Did you send EECU and injector off to Brucato to have tested/cleaned? Sounds like you got a bad MAP in ECU or injectors are flooding..
 

mkeleher

Seaman
Joined
Feb 18, 2012
Messages
58
Re: RPM's on a 200 mercury

Faztbullet,

First off wanted to say thanks for your help on my motor issues. I've had problems with my motor from the time of purchase and everything you have told me has pretty much been spot on. I took your advice and called Brucato earlier today. Extremely nice knowledgable people. Im going to send my ECU to them to test before I send off the injectors. I'll start with the small inexpensive things before I start spending on injectors. If indeed my MAP is bad in my ECU, can that be fixed or is it time to break out the checkbook on a new computer?
 

Faztbullet

Supreme Mariner
Joined
Mar 2, 2008
Messages
15,616
Re: RPM's on a 200 mercury

If indeed my MAP is bad in my ECU, can that be fixed or is it time to break out the checkbook on a new computer?
If bad buy Tonys(Brucatos) ACU and replace yous as: (1) it adjustable and (2) about 1/3 cheaper than a Merc ECU. I Like his as if you bore one over size you can fatten it up with adjustments at midrange and top end. Below is pic's of one I was dialing in on a test prop..note that ECU is turned over to adjust trim pots.
 

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Dukedog

Captain
Joined
Oct 6, 2009
Messages
3,245
Re: RPM's on a 200 mercury

Just gonna through this out there. '91 should be a fat block. There is no such thing as a chrome bore 2.4 fat block. '91 200's are 2.5 steel sleeve motors. Do you have pictures (port side)? Have ya found a "build date" on it? Might be "Heinz" motor. Either way like fb says, ecu, injector type problem maybe.................

JAN....A early analog 2.4 ecu ona 2.5 motor really sucks...............jmo
 
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mkeleher

Seaman
Joined
Feb 18, 2012
Messages
58
Re: RPM's on a 200 mercury

I'll get some pictures and no I cannot seem to find a build date on this motor. Quick question, can a bad ECU mess with a stator and possibly blow it? Reason I ask is when I installed the new stator and volt regulator the battery would charge great. After running the motor again at WOT to see RPM's the stator is bad again.
 

Faztbullet

Supreme Mariner
Joined
Mar 2, 2008
Messages
15,616
Re: RPM's on a 200 mercury

No on the ECU/stator question but a 35amp flywheel on a 16amp stator will fry a stator and retifier in a heartbeat!!!
 

mkeleher

Seaman
Joined
Feb 18, 2012
Messages
58
Re: RPM's on a 200 mercury

just did a test on the stator and rectifier and they are both fried chicken AGAIN. .3 ohms out of one set of charging wires from stator and nothing out of the other set. Rectifier reads 45,000 out of both yellow wires and the red wire. On both individual packs. Something is making these fry cause they were charging great before I went out and ran the motor. Im surprised that the computer isnt screwing with the stator. Either way, the computer is going to brucato's tomorrow for evaluation. Any other suspects with the ignition that might make these blow? Switchboxes?
 

mkeleher

Seaman
Joined
Feb 18, 2012
Messages
58
Re: RPM's on a 200 mercury

Update:

Called CDI today about stator and rectifier blowing again. 2 Potential problems. I have a maintenance free battery rather than a flooded cell battery which could be throwing things off. Also, the ECU could be throwing mixed signals to the ignition components in turn burning up the stator and Rectifier. Getting ECU evaluated and going to buy a flooded cell battery.
 

mkeleher

Seaman
Joined
Feb 18, 2012
Messages
58
Re: RPM's on a 200 mercury

Update:

Tony checked my computer and said the ECU was functioning correctly but that the computer is for a 220 laser rather than a standard 200 efi. He said it shouldnt effect how my motor is currently running. Looking at the injectors next. Has anyone heard of a maintenance free battery continuously blowing stators and/or rectifiers? I find it hard to beleive that the battery could be blowing my charging components. Its a brand new battery.
 

Dukedog

Captain
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Oct 6, 2009
Messages
3,245
Re: RPM's on a 200 mercury

Update:

Has anyone heard of a maintenance free battery continuously blowing stators and/or rectifiers? I find it hard to beleive that the battery could be blowing my charging components. Its a brand new battery.

I'm with Fb on this one..............Gonna add. Did ya ever determine if its a 2.4 or 2.5? '91 was a "strange" year for some of tha builds! Pictures of tha motor will identify it. Port side of tha block. Reed plate.........
 

mkeleher

Seaman
Joined
Feb 18, 2012
Messages
58
Re: RPM's on a 200 mercury

I'll get some pics tonight and repost. Pretty sure its a 2.4 though. The 2.4 throws a 40amp stator correct?
 
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