2008 50 HP Mercury 2 Stroke Engine loses RPM when underway.

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ipukula2000

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Apr 27, 2014
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I have a 2008 50 HP mercury 2-stroke engine. It has had a problem for about a month with starting. I checked compression (each cylinder was 120 psi), installed new plugs (gapped correctly), installed new fuel bulb, new battery, and have removed, installed new fuel filter and gas/water separator and removed and cleaned all three carburetors. I also had the shift and throttle cables replaced by a marine mechanic (the throttle cable was rusting through). The motor now starts great and I took it our yesterday. Everything was great, at full throttle I had the usual 4,500-4,800 rpm with three people on the boat (17' flats boat). After about 5 minutes, however, the rpm suddenly dropped to 2,800 and wouldn't rise above this number the rest of the day. It ran fine at 2,800 rpm. If I put in neutral, the RPMs easily rose to 4,000-5,000 (I didn't push it any higher!). I re-engaged the shift, put in Forward and could still only get 2,800 rpm. This has never happened before. Today I checked in a trash can of water (adding resistance to the prop) and it worked fine, back up to 4,500 rpm near full throttle.

Any ideas?
 
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I have the exact same problem except I have a 2006 4 stroke. it rolls around 2600-2800 RPMs. I have done almost the identical things, still nothing. Did you ever solve your problem from April 27th???
 

ipukula2000

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Yes, I solved the problem. It turns out that my first cleaning of the carbs was not too good. I removed the carbs a second time an really cleaned them good with carb cleaner. I also ran a small wire through all of the holes in the carb. My cycle was...spray carb cleaner all over disassembled parts. Then, run wire through all the holes I could find. Then, blow out with compressed air (I have a cheap Home Depot compressor). Then, one last spray with the carb cleaner. Then, I waited until they were completely dry. I reassembled and the motor started right up. I took it out the next day and absolutely no problems. In fact, my RPMs were as high or slightly higher than the day I bought the boat! It only took a couple of hours for this as I am now very good at taking off my carbs after all this!

Good luck with it!!!! It was a very frustrating problem!!!
 

ipukula2000

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Apr 27, 2014
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Yes, I solved the problem. It turns out that my first cleaning of the carbs was not too good (although they looked very clean!). I removed the carbs a second time an really cleaned them good with carb cleaner. I also ran a small wire through all of the holes in the carb. My cycle was...spray carb cleaner all over disassembled parts. Then, run wire through all the holes I could find. Then, blow out with compressed air (I have a cheap Home Depot compressor). Then, one last spray with the carb cleaner. Then, I waited until they were completely dry. I reassembled and the motor started right up. I took it out the next day and absolutely no problems. In fact, my RPMs were as high or slightly higher than the day I bought the boat ~5,200 with just me)! It only took a couple of hours for this as I am now very good at taking off my carbs after all this!

Good luck with it!!!! It was a very frustrating problem!!!
 

AnthonySci

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Dec 4, 2016
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Did your problem of not getting up on on plane at WOT ever re-occur? Were one of the carbs gummed up again?

My 2005 50 hp Mercury 2 stroke is following the same pattern except it only happens sporadically.My guess is that 1 of the hi speed jets has some type of gummed debris that "liquifys" from the normal heat produced on the block--THEN the gas gets through the hi speed jet and my motor runs strong and up on plane at WOT !
 

GA_Boater

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Did your problem of not getting up on on plane at WOT ever re-occur? Were one of the carbs gummed up again?

My 2005 50 hp Mercury 2 stroke is following the same pattern except it only happens sporadically.My guess is that 1 of the hi speed jets has some type of gummed debris that "liquifys" from the normal heat produced on the block--THEN the gas gets through the hi speed jet and my motor runs strong and up on plane at WOT !

The OP left more than 5 years ago. If you want advice from active members, start a new thread.

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