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Rpms plummet at 5k

P

play2win

Member
Hey gang, been a while - been having similar problems as Eluders recent post. Boat cruises fine under 4500 rpm, at 5k....the engine bogs down to around 2k, and sometimes "kicks in" again before I come off plane. Compression good, spark all there, replaced in line filter, and water separator. Should I go with plugs now? Thought it was fuel issue, but not quite sure now. Also, took out carbs and cleaned them up last weekend
 
check your back-flow preventer, otherwise known as an anti-siphon valve.
I had similar issues with my current boat and it drove me nuts. In the end I
removed the back-flow preventer and replaced it with a regular barbed fitting.
problem solved.
 
Hey Play2win, if you have an inductive timing light or inductive tachometer, hook it up and run the motor and see if you lose ignition at high rpm. If the ignition stays strong then you would be looking at fuel supply. I urge caution, if you are going lean at high rpm you can damage a 2 cycle engine very quickly. If the ignition fails at high rpm then you would look at checking stator high side, rectifier/regulater, idle stabiliser, or switchboxes. If I remember correctly, you are running a Merc motor.
 
I had a leaky head gasket that cause a very similar issue. I was able to replace it while in the water and was good to go.
 
Hit or Miss

Well I cleaned the gunk from the fuel lines added Sea Foam and I finally installed a fuel/water seperator that has beed sitting on the shelf for years. Took her out and all seems good! 3 Adults and a 10 year old for weight and ran that Merc Flat OUT and no sputter etc, but it still feels like I'am not going as FAST as I remember??? TO top it off my TACH is way off at idle it is 1200 RPM off according to my Lazer Tach., all connections are good but need to verify the Rectifier again-Anybody have a similar issue-I think its the Tach but your guess is better then mine until I check the Rectifer!!! Happy Boating.... Eluder...
 
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