Unclejake Posted August 23, 2009 Share Posted August 23, 2009 Yamha 40hp carburetted three cylinder oil injected outboard motor. It has been running perfectly for years, serviced about 40 hours ago and always looked after etc. We use it moist weeks and this weekend did close to 20 miles without a problem until we were steaming toward home on Saturday. All was well until we wanted to anchor somewhere and then suddenly the motor kept coughing and stalling at very small throttle openings or at idle. Under load it is fine, and was fine on the final leg of the journey after we pulled up the anchor and made for the shore. Back at the shed it was coughing and sounding 'off song' when we were washing it. A compression test showed 125 psi on all clyinders so I cleaned the plugs and put it back together. At idle it still coughs and stalls. At a fast idle it keeps running but sounds 'wrong', a bit like the timing being out. Where the exhaust note used to be a sharp 'crack' it is now more of a dull 'pock'. I put the timimg light on it but couldn't get a reliable signal from any of the three coils. The ignition trigger seems to be a magent pressed into the flywheel. The only thing that we changed in the last week are the battery cables to the powerhead and I did stress the fuel line a bit which could have introduced an airleak into the fuel system (which I have not checked for but the fuel filter was full of fuel) Any ideas two stroke masters? Quote Link to comment Share on other sites More sharing options...
kyteler Posted August 23, 2009 Share Posted August 23, 2009 Haven't read all through just yet... got to; We use it moist weeks ...and chuckled. Will continue to read dilemma now. Quote Link to comment Share on other sites More sharing options...
kyteler Posted August 23, 2009 Share Posted August 23, 2009 Sound like a fuel delivery issue to me? Quote Link to comment Share on other sites More sharing options...
sheepers Posted August 23, 2009 Share Posted August 23, 2009 id like to buy "blocked idle jet" for 10$ please. i reckon you might get some wins if you give the carb/s a clean. sheepers Quote Link to comment Share on other sites More sharing options...
Black Francis Posted August 24, 2009 Share Posted August 24, 2009 yeh im with that sheep on the blocked jet idea happens all de time on lawnmowers. Sometimes will only run if you stand there pumping the primer and play with throttle or something like that. then you clean jets and they runs goods. or maybe like carb gaskits/diaphrams/stuff like that. That stuff is always causing poor running. Does it idle good with the choke on? its alwayz the the bloody carbs that give me trouble Quote Link to comment Share on other sites More sharing options...
Borgweiser Posted August 24, 2009 Share Posted August 24, 2009 If its not the blocked jets which would be my first guess too, im going for air leak.. Check for cracks in manifold as im sure Yamaha uses rubber manifolds or possibly a crankcase seal has had it Quote Link to comment Share on other sites More sharing options...
ESKIN8R Posted August 24, 2009 Share Posted August 24, 2009 wouldnt hurt to throw some new plugs at it Quote Link to comment Share on other sites More sharing options...
Black Francis Posted August 24, 2009 Share Posted August 24, 2009 yeh i reckon air leak if it runs good on partial throttle or with the choke iduno outboards tho but thats what happens with hedge trimmers lol buy a carb rebuild kit or if its got those rubber conector things btween the carb and engine like motor bikes then check for cracks/ tighten the hose clamps cos that happened to my friends bike and it produced similar results Quote Link to comment Share on other sites More sharing options...
Unclejake Posted August 25, 2009 Author Share Posted August 25, 2009 The carbs are solid mounted. I got some spark plugs today so will try that tonight but I doubt the plugs are the issue. A blocked idle jet sounds likely, but the change in exhaust tone had me thinking it was timing. If it is a blocked idle jet I think I will take it to an outboard specialist. Quote Link to comment Share on other sites More sharing options...
My name is Russell Posted August 25, 2009 Share Posted August 25, 2009 Have you got petrol in the tank? Quote Link to comment Share on other sites More sharing options...
Unclejake Posted August 25, 2009 Author Share Posted August 25, 2009 New plugs didn't help (as expected) so I blew through the carbs with compressed air and the problem has gone away. Thanks team. Sheepers (and others) probably had it right. Low'N'slow............ you are a dweeb Quote Link to comment Share on other sites More sharing options...
My name is Russell Posted August 25, 2009 Share Posted August 25, 2009 Sorry if there is fuel in the tank i can't help you any further ... checked battery terminals? Quote Link to comment Share on other sites More sharing options...
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