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Old 11 December 2010, 14:41   #1
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Whats wrong with my engine?

Hi I am having a problem with a 4hp four stroke Yamaha , I had a job starting it up and it only goes with the choke out and runs very rough , when I push the choke in it cuts out , I took the carb off and blew it out with air and took the plug out and cleaned it. What else could be wrong, the fuel is getting to the carb. Can anyone give me any advice as to what it could be, thanks.
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Old 11 December 2010, 15:33   #2
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It sounds like fuel contamination see my thread here similar problem though different engine: Mercury Sailmate 4hp problem

Did you take the main and idle jets out and blow those through with an airline properly? If not, that's probably where to start.
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Old 12 December 2010, 07:32   #3
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4hp yamaha

Hi , YES this sounds like a fuel issue . we do have issues on these all the time and 99.9999% of the time its fuel related.Igntion system on these are pretty good . YOU need to take that carb off again and carefully remove all the jets inside etc . I do a Carb , injector CLEANING SERVICE for outboard engines and charge 25.00 for small engine per / carb . I run this thru a ULTROSONIC Cleaning machine and set it all up after cleaning . You may aswell remove the fuel pump on this aswell and check the pump in working correctly with a vacuum pump , make sure the diaphrams inside are all ok .WHat is you MIXTURE SCREW SETTING ????
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Old 12 December 2010, 11:04   #4
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thanks for the replies , sorry dont know about screw setting. I had a problem before and carefully removed the carb as I had never done it before, blew it out with air ,reassembled and to my delight it went grand, now having it again so was wondering was it something else as it wasnt run much since I took it apart.
Is the fuel pump difficult , as I would like to learn but not f up the engine and have to bring it to someone to reassemble
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Old 12 December 2010, 14:37   #5
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Personally I think you just missed some poo in the carb, how many jets did you take out? You need to take them right out and give each nozzle on each jet a toot with 100psi+ of compressed air to make sure they are all clear. Worked on mine anyway. Did you take the float chamber off and clean that out too?
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Old 12 December 2010, 14:38   #6
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Quote:
Originally Posted by davis View Post
thanks for the replies , sorry dont know about screw setting. I had a problem before and carefully removed the carb as I had never done it before, blew it out with air ,reassembled and to my delight it went grand, now having it again so was wondering was it something else as it wasnt run much since I took it apart.
Is the fuel pump difficult , as I would like to learn but not f up the engine and have to bring it to someone to reassemble
where in Ireland are you ?
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Old 18 December 2010, 11:09   #7
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F4 Yam

Hi,

I know for a fact that the F4AMH Yamaha has 'Jet' issues... Yamaha replaced the jets & sometimes whole carburetor under warranty if the problem persists... If you can, contact a Yamaha dealer and see if they will help you with possibly a new carb...

www.mobileoutboardservices.com
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Old 18 December 2010, 14:46   #8
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I am in the south east, thanks for the advice MOS , stripped the carb again today cleaned and blew it out , changed the oil , put back together and it started and ran for a while then I turned it off. Tried to start again and no go so maybe what you are saying may be the problem , but the engine is not in warranty anymore so probably no hope of a new carb from them. I was going to try the fuel line and pump next to see if there is any dirt in there ,other than that I dont know , but the fact that it started and run it must be a fuel problem.
These engines are not easy to get at everything seems to be packed in around each other.
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Old 18 December 2010, 17:09   #9
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I had this problem,

Make sure the tank does not have crud in as you can keep cleaning out the carb and the carb will keep getting crud in from the tank.
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Old 18 December 2010, 17:15   #10
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When I did mine I took the tank right off, drained it out, and sloshed a bit of clean fuel around in it then drained that off, did it 3 or 4 times just to make sure. Nothing in the tank of the Merc, but when I had fuel problems with the old Johnson aux it was crap in the tank. Small engines tend to have the fuel pickup right more or less at the very lowest point rather than having any sort of sump, which is great until you get some crud in the tank then it is the first thing that exits via the pipe...
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