Points gap on yamaha 3.5hp outboard engine - Yamaha Boating

.025"
you should be using multi discharge point plugs in out board motors -not regular car engine plugs and the gap is preset on them
the reason being , with multi point discharge they are less likely to foul from oil and carbon build up
available from any good auto parts shop or marine shop

try this

http://www.yamaha-motor.com/assets/service/manuals/2004/lit-18626-05-34_869.pdf

manuals are freely available on the yamaha website

0.040mm

0.024
http://www.globaldenso.com/cgi-bin/global/plug/usa/pw/pw-plug.cgi?filename=pw-14.txt

I Would Recommend a 0.8 Gap

1. Fuel
   • A common problem with an easy solution, Yamaha boat engine trouble could arise due to inadequate levels of fuel or engine oil. All Yamaha outboards take unleaded gasoline as a main fuel source with a pump octane rating of 86 or higher. The type of engine oil varies according to motor size and can be found in the "Specifications" section of a particular outboard's owner's manual (See Resources).
     
   Electrical
   • Problems with the electrical system can also prevent a Yamaha outboard's engine from working correctly. Troubleshoot the electrical system, first removing the main fuse that's located underneath the electrical panel on any electric-starting outboard. If the connection at the center of the fuse is broken, it must be replaced by a fuse of the same amperage. The battery should also be removed, cleaned and fully charged when troubleshooting the electrical system.
     
   • 
     
   Spark Plugs
   • Owners should also remove and inspect the spark plugs during the troubleshooting process. If the insulator tip of any plug is burned, that spark plug should be replaced. The number and type of spark plug depends on the specific outboard. Additionally, owners should ensure that each spark plug gap is set to the width stipulated in the owner's manual (see Resources).
     

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.

The correct gap is .035

For a 2001 Yamaha F115 4 stroke use NGK Plugs LFR6A-11 gapped between 0.039 and 0.043