SOURCE: does my 2000 honda 4 stroke 8 hp outboard have a fuel filter?
Your tech may have missed one or two parts of the idle circuit. There is an idle mixture screw hidden under a brass plug (to prevent tampering on the top of the carburator. This passage needs to be cleaned and idle air mixture screw adjusted properly.
There is also an idle air jet located close to the idle mixture screw. The jet should be removed and cleaned as well as the passage that it came out of. The jet is a small brass piece with a small hole and a standard screwdriver slot. Unscrew this, spray brake cleaner through the little holes and spray brake cleaner (using the little straw that comes with the brake clean) into the hole in the carburator. Take some compressed air ( from a small can of compressed air that you use to clean your computer) and spray into the hole. Reinstall the jet and see what happens. If this does not fully fix it, I would return it to whomever originally cleaned it. If the dealer is worth their salt, they will fix it (if they did not clean in the first place) Everybody makes mistakes.
Also, be sure that your oil level is not too high. It is better to be a little low than too high.
Be sure to be using NKG spark plugs DR5HS I assume that both spark plugs look ok.
The other item that affects this motors idle is the thermostat. Feel the top head of the motor. It should be about 130 degrees. Not hot enough to only just touch, but not cool enough to be able to keep you hand on for 10 seconds or more. A temperature gun would tell you for sure, but most people do not have those is their back pocket.
Timing could be an issue, but normally, it would affect all speeds of operation.
A lot of things for such a little motor.
SOURCE: yamaha outboard 150 4 stroke bad vibration at 700
is you propeller bent? a dent the size of a quarter will cause a shake. If not that means your engine is misfiring. here are the troubleshooting test and tool list you need to find out. Tools(1) A compression gauge (2) a spark gap tester.(3) A Clymer service manual for your engine. (you can purchase from your local outboard dealer. I know all these are expensive but if your going to be a outboard tech you will always need them. Troubleshooting (1) check compression. without the year model I'm giving you a average numbers. Look at your Clymer manual. all cylinders need to be over 100 lbs and equal each other within 5 lbs.(2) check spark. use a spark gap tester all cylinders should jump a half inch gap. if you have good compression and good spark, fuel is the problem nine times out of ten.Ethanol gas is proven to stay stable in fuel systems for 30 days in 90 + degree heat. Drain gas tank,clean fuel lines replace primer bulb and replace all fuel filters. Yamaha has a gravity filter under engine coul clean it. Finally replace spark plugs, I know spark plugs probably don't look bad but this is a outboard. Fresh spark plugs means less resistance for the ignition system. The ignition system is week compared to automotive. Test drive boat, if the problem is still there then there is further steps to take. Again I don't know the year model so I guessing its fuel injected. Pull out your clymer manual. what is great about the Clymer Manual for Novice techs is it gives detailed info on your outboard. Troubleshooting tips and teaches you how your outboard works.
SOURCE: i have a 15 hp
Remove top cover to find serial number on cylinder head.
Contact manufacturers here
http://www.marineroutboards.co.uk/main.php
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