98 Johnson Ocean Pro 200 HP..dropped RPM

[finnaddict98]

My motor was running fine at 5500 RPM when the rpm dropped suddenly to 4500 RPM and felt as if something was being dragged behind the boat (nothing was). The throttle will still advance and the mechanisms on the carb have full movement but the motor will not exceed 4500 rpm. I put in new plugs last week and it ran just fine then. There is no smoke, water press/temp is good. No alarms sounded. I have no idea what the problem could be..any suggestions before I spend big bucks on repair????

 

[clanton]

Re: 98 Johnson Ocean Pro 200 HP..dropped RPM

I would lift the cover to see if anything fell off or burnt up, if not start with compression, spark test. To do the spark test you need to bypass the quickstart circuit. If I had to guess power pack.

 

[ReelRaider]

Re: 98 Johnson Ocean Pro 200 HP..dropped RPM

Is this Finnaddict from allcoast. This is ReelRaider and a just purchased a Avon Seasport 4.25 with a Mercury 50hp. Have problems with an alarm. Have posted here but not on Allcoast. I must be in the right place. Sorry I can't help you - know about gas/desiel but no outboards. I guess that's why I'm here...<br /><br />Al - the ReelRaider - We should go fishing together sometime.<br /><br />

 

[JB]

Re: 98 Johnson Ocean Pro 200 HP..dropped RPM

Sounds like you dropped a cylinder, Finnaddict. Pull spark plug wires, one at a time, until you find one that doesn't cause the engine to slow. That is a cylinder that is not making power. See if the plug wire will arc 1/2" to the block. If not, you have an ignition problem. If you have the spark, you probably have a fuel problem.<br /><br />Good luck.<br />Red sky at night. . .<br />JB

 

[hondon]

Re: 98 Johnson Ocean Pro 200 HP..dropped RPM

A dropped cyl. certainly fits the profile here. Your task is to determine ignition or fuel or mechanical.First, do a compression test.Then if all looks good ,put her on the water and with a timing light,move that light s inductive pickup from plug wire to plug wire.Point the timming light at your face and compare the differences between cyls..Much safer than pulling plug wires at this RPM.All looks good there ,then remove the airbox cover and inject a little 50 to 1 fuel mix into each carb via a spray bottle from your paint store.Any change,a carb rebuild is in your future.

 

[JB]

Re: 98 Johnson Ocean Pro 200 HP..dropped RPM

Hey, Finnaddict. Hondon's approach to finding your cause looks a lot better than what I suggested. Go with Hondon's suggestions.<br /><br />Red sky at night. . . <br />JB

 

[finnaddict98]

Re: 98 Johnson Ocean Pro 200 HP..dropped RPM

Hondon....I pulled the plugs and one of them looked as if it wasnt doing anything under power...the part of the plug that usually is chocholate brown is white...the other plugs look good. Im kinda torn between a power pack, coil or the part the spark plug attached too...that I cant remember the name of right now...would you think that simply the plug itself is bad and maybe just replace that single plug and go from there????null

 

[hondon]

Re: 98 Johnson Ocean Pro 200 HP..dropped RPM

If you have failed igniton on just one cyl,that plug will usually come out very wet with unburt fuel. That white electrode could indicate a very lean condition or conceivabley a blown head gasket.

 

[Big Four]

Re: 98 Johnson Ocean Pro 200 HP..dropped RPM

Before you even start that thing again I would check the compression in that dead cylinder. If she tripped over or broke a ring, running it is the last thing you want to do.<br /><br /> Swap that dead plug to another cylinder for a quick check to see if the plug is bad. Just in the last two years I've come across 5-6 bad Champions, before that it was 10 years since I've seen a bad plug, so it wouldn't surprise me if you had one bad plug. Especially since you just changed them.. If that plug porcelin looks white(new) from not firing I doubt it ever was firing. <br /><br /> After that you can check coils by just swapping them into a different positions. If the problem follows that coil you've found the problem.