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Jason, Marine Mechanic
Category: Boat
Satisfied Customers: 14831
Experience:  Degree in Marine Technology. Gas and diesel marine mechanic.
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2006 mercury 40hp 2 stroke losing about half power at full

Customer Question

2006 mercury 40hp 2 stroke losing about half power at full throttle...cones and goes but you can push the choke momentarily and engine speed will stay up....
Submitted: 1 year ago.
Category: Boat
Expert:  Jason replied 1 year ago.
Hello my name is ***** ***** am I speaking with?
Couple questions back to you. First, how old is the fuel? When did the engine last make full power? Has it been sitting a long time?
Customer: replied 1 year ago.
My name is ***** ***** boat...I have run probably one tank of fuel...previous owner had fueled it up about a month ago...boat was running fine (pontoon) then rpms dropped from 6000 to around 4000 while still at full throttle.. had some trouble starting after that and would die when putting into gear.. in neutral will Rev up but with a little hesitation. I could tap the choke intermittently to keep rpms up at 6000
Customer: replied 1 year ago.
I ran the boat yesterday
Expert:  Jason replied 1 year ago.
Hi Tim,
When you say "I could tap the choke intermittently to keep rpms up at 6000"
Are you reving the engine in neutral doing that? Or is that with the boat in the water and in forward gear?
Customer: replied 1 year ago.
Yeah...on the river moving forward trimmed out
Customer: replied 1 year ago.
Plugs look good...linkages look good..has some black gunk in fuel filter
Customer: replied 1 year ago.
Small amount
Expert:  Jason replied 1 year ago.
Gotcha. If that's the case the problem is going to be 1 or more of the carbs is slightly clogged, and not flowing enough fuel. The reason I say that is the engine does not have a traditional "choke". Instead what it has is what is called a primer solenoid. What a primer solenoid is, is like a little fuel injector. It injects fuel directly into the engine on a separate circuit that is separate of the carburetor. The reason I say it's the carbs is because if they were flowing fuel properly, then activating the choke/primer would cause it to run to rich, and it would run worse, and not better, does that make sense? And if there is black gunk in the filter, that again points to the carbs, as those filters don't catch everything.
Customer: replied 1 year ago.
Something else I noticed while engine was running...fuel filter was pretty much empty so I pumped it up to get more fuel in it...should it get hard to pump or will it just relieve itself back into the tank?
Customer: replied 1 year ago.
Yeah...if I kept the choke in too long the engine would bog down worse
Expert:  Jason replied 1 year ago.
Well if pushing in the choke for to long did make it run worse then there is something else going on here. And the engine really needs to have its compression and spark tested first. Is that something that you have the tools for, and think you can do?
Customer: replied 1 year ago.
Yeah...I have the tools and mechanically inclined..pushing the choke would give more fuel correct? Causing it to be feeling all along has been fuel related
Expert:  Jason replied 1 year ago.
Pushing the choke does give more fuel. Before doing any testing at all my gut says the carbs are gummed up. But I want to rule out a compression or spark problem first.
Customer: replied 1 year ago.
Top cylinder is 110...middle is 115 and bottom cyl is 112
Expert:  Jason replied 1 year ago.
Got it. Those are good numbers. Do you have a timing light or a spark tester to check spark on all 3?
Customer: replied 1 year ago.
Spark tester.. good spark all three cylinders
Expert:  Jason replied 1 year ago.
Got it. At this point I would feel comfortable rebuilding the carbs. Also, if you don't have one, it would be a good idea to install a fuel/water separating fuel filter between the tank and the engine, the engine mounted fuel filters don't catch much in terms of debris, and they don't catch any water at all either.
I think that should do it. If you had a further question on the issue by all means feel free to ask. If not, Just incase you do not understand the way the website works (and some folks do not). You do have to put forth a positive rating in order for it to credit me for helping you. When ratings are not done, the website simply keeps your deposit and they will not credit me. Please let me know if you run into any problems or errors when trying to do it. If you do have a problem, just reply back "I rate Jason's service _______" and fill in the blank.
Questions do not lose out, so if you have to come back tomorrow or next week with follow up questions to this you still can even after doing a rating. And if I have saved you quite a bit of money, or saved you a trip to the dealer, tips are always greatly appreciated.

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