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Discussion Starter #1
Give it throttle and it tops out around 3k. Don't think its a fuel issue, just did a carb job and checked all fittings, and fuel looks fine.

It was misfiring @ idle intermittently this AM, so I checked all connections, plugs, wires, etc. (BTW pretty sure I got zapped a bit when I pulled the cowling). Idle smoothed out but still no top end.

Any ideas?

Thanks!
 

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My troubleshooting routine from a previous post...


When an outboard acts up, it can be the most frustrating thing to deal with.
But the rules are simple...Air, fuel, spark, timing, compression, cooling, lubrication.
Any of the items listed above can affect how your outboard runs.

My outboards are carbed and my trouble shooting routine is this:

Check the kill switch...make sure it's not activated.
Verify the vent is open on the tank.
Quick visual check for spark at plugs, condition of plug tips. Clean if covered in crud.
Drain fuel tank, check for contamination by dirt or water.
Verify interior of fuel tank is clean, including pickup screen.
Air leaks between the tank and pump have to be eliminated.
That means every fitting from pickup tube to the fuel pump has to be inspected and tested.
Brittle or cracking fuel hose and primer bulb means time to replace.
O-rings in connectors may need replacing.
Verify hose integrity from connector to fuel pump, including last-chance filter.
Clean or replace fuel filters, check water separator.
Pressure test fuel pump to verify function.
Verify hose integrity between pump and carb.
Hoses under the cowl are exposed to heat-vibration and get brittle. Replace if needed.
Check intake vacuum pressure.
Check integrity of scavenger tube from crankcase.
A cracked or broken tube changes the fuel/air ratio.
Rebuild carb, verify every passage is clean and clear.
Sometimes bits of metal from the machining process make it into the carb.
Solvents won't remove those bits from the idle passageways.
A manual/visual inspection has to be done to ensure a true and complete cleaning has been done.
Replace the carb float, don't keep using the old one, they do leak and lose buoyancy.
Replace float valve and valve seat, vibrations will change the shape of the tip and seat, they won't seal properly.
After reassembling carb and installing, check linkages and throttle sychronization.
Verify choke settings and idle settings.
Run compression test.
Replace spark plugs, one of the easiest things to do to make an outboard run better.
Plugs don't last forever, recommended replacement is after 300 hours of use or 3 years, max.
Replace spark plug wires at 5 years due to resistance build up and cracking of insulation.
Run outboard at night with cowl off, check for visible sparks, including from under flywheel.
Check spark with a spark gap tester, easy to buy or make one.
Obtain a volt-ohm meter and learn to use it.
Use the meter to test the ignition components, specs are in the OEM manual.
Coils, CDI controllers, sensors, stators have specific resistance readings at each wire connection.
if readings are outside OEM manual parameters, replace.
On older outboards, check ignition timing.
Check throttle cables for fit. Any play or looseness can result in low rpms on the water.
Ensure proper oil levels are maintained in 4 strokes, proper mix in 2 strokes.
Check water pressure exiting block, check thermostat, poppet valve.
Check engine overheat sensor. (again, info in OEM manual )

Lots of steps there, but it's what I have to do sometimes
in order to find the problem...or in some cases, problems.
 

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Discussion Starter #4
Sorry. 99 25hp Merc 2st.
 

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If it skipping bad then it will more than likely be an ignition system; you should be able to tell visually and hear if the motor is skipping, but the RPM’s are getting pretty high to be an ignition problem. I would pull the carb cover off while running it put your hand over the crab for just a second, you are basically acting as a butterfly choke, since that motor doesn’t have a choke. If it picks up RPM’s you have a fuel issue not an ignition problem.
However the 1st test before all other test should be a Compression test!!!!
 

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Discussion Starter #7
Picking up a compression tester tomorrow. Thanks.
 

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since u got shocked,run the motor cowling off in the dark and look for fireworks
.

X2

And if at first you don't see the fireworks - mist it with the garden hose and vary the rpm's. Gotta be dark - not dark outside and under the garage light.
 

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since u got shocked,run the motor cowling off in the dark and look for fireworks
.

X2

And if at first you don't see the fireworks - mist it with the garden hose and vary the rpm's.  Gotta be dark - not dark outside and under the garage light.

^  [smiley=badidea.gif]  Okay I have bitten my tongue on previous post about running the motor at night; but I have to say this is not the correct way to diagnosis an engine. That is what some junk yard mechanic would do, NOT A MARINE TECHNICIAN; To the OP it is highly unlikely that you were shocked from the engine while pulling the cowling off, If there is something arcing it’s taking the easiest resistance to ground and I highly doubt your hand on the engine cowling would be the easiest path to ground unless your grab the ignition coil wire ( Not calling you a liar just saying that it's not likely), In 15 years of working on Marine engines I have never been shocked other then when I have touched the Ignition coil wire.

The reason why I gave my previous suggestion was that it’s only a 25hp which means it’s a 2 cylinder and if you’re losing spark chances are you would never get to 3k rpm’s

Here are the 1st couple of correct procedures to diagnosis all marine engines. You have 3 needs to make and engine run, Compression, Spark, and Fuel.

1st Compression Check (Always 1st) any reputable Technician will always do a compression test 1st.

2nd A Spark test (Running the engine at night is not how you do this or any other test I have ever been taught at Yamaha, Mercury, OMC, BMC, or Suzuki school)

3Rd Fuel Test (Depending on the engine would determine how this is performed) 
After these 3 steps have been performed and only AFTER can you move to other trouble shooting procedures.
 

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running the motor at night...That is what some junk yard mechanic would do
Dang...all this time I thought it was ******* tech!   ;)


For those of us without a shop full of proper tools, the night time/cowl off/spark spotting technique
is a quick way to find cracked spark plug wires, loose connections, and improperly grounded components
that otherwise would require real tools and the knowledge to operate said tools.

It took me a few years and several boats before I got past that level of outboard electrical diagnosis.   :-[  ;D
 

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I can see your point of not having all the special tools and required skills to use them; However you don’t need any special tools to diagnosis a 1999 25hp Merc 2Stroke. And if you did a proper visual inspection of all wires, and checked all connections in the day time, you wouldn’t find anything at night that you wouldn’t know already.

If I was working on the engine the only tools I would need is a screwdriver set, a socket, and wrench set.

I just don’t see the purpose of doing it, I just feel it’s a 2nd rate way of doing something, and like you said it took you a couple of years to graduate up; well if people didn’t give bad advice and improper ways of doing things people could learn the correct way much faster.

I’m a newbie around here and I’m not trying to make waves, but there are I know of at least 4 (Probably many more) including myself Marine Technicians on here that have the proper knowledge and skill set to give correct and proper advice. Instead of saying run your motor at night and look for the blue sparks, You could say visual inspect all wires for cracks in the insulation and make sure all grounds are tight. However you should still start off with the 1st 3 steps I said earlier ALWAYS, ALWAYS, ALWAYS. Until that is done you’re just guessing!!!
 

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I’m not trying to make waves
You ain't...in order to make waves around here, you'd have to be dissing gheenoes.  ;)

All you've done is offer comments from the point of view of a trained professional
dealing with barely competent amateurs. I've got no problem with that.
I read all these diy posts, never know when I might have the same problem.
Comments from a professional mechanic are especially valued.
I was taught a long time ago: Never argue with a pro, listen instead, I might learn something.

                                                    [smiley=happy.gif]

                                                
 

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Discussion Starter #13
FWIW it was the control module.
 

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TRW I want to thank you very much for taking the time to report on what the problem was. So often we never hear back and wonder if it was our suggestion or someone elses that solved the problem.

Best regards,
Frank_S
 

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Discussion Starter #15
No problem. After I had it figured out I looked at the troubleshooting guide in the manual. Right there in black and white it said "timing will not advance= faulty control module".
Maybe I'll read more carefully next time!
 
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