Posts: 829
Location: Maple Grove, MN | Could be a diaphram all right. That would probably be the best scenario. Could be something else too.
I had gas get into my F115 Yamaha a few years back. The problem was that the engine wasn't running correctly due to plugged fuel injectors. The gas was not being burnt in the piston so it leaked down into the oil pan. I would do the following:
If the motor is running poorly (lack of power, slow hole shot, etc.)
1. Check the spark plugs. Make sure the gap is set correctly and replace if old.
2. Check to make sure all spark plugs are getting spark.
3. This could be water related. Do you have a 10 micron gas filter on your boat? If not, add one. If you do, replace it. It could be full of water. This also will prevent fuel injector plugging which can be expensive to fix on these motors.
4. The motor could be loaded up with carbon. Get a bottle of Yamaha Ring-Free and follow the directions.
Other possible problems:
1. The engine could be running to cold:
* Running an F115 slowly to much, like at trolling speeds, can prevent the motor from heating up properly and cause gas to not burn off completely and end up in the engine oil.
* A faulty thermostat can cause the same problem.
* Incorrect spark plugs, as in not hot enough, will cause the motor to run cool. Make sure the plugs are those listed in the owners manual.
2. You may have gotten bad gas. If possible, use non alcohol gas.
3. One of your fuel injectors could be plugged up like on my motor. This was a big deal for me because the first mechanic blew all four fuel injectors out with compressed air and destroyed them. The injectors must be cleaned in a special process. Your mechanic would need to send the dirty injector(s) in to get cleaned. The entire job should cost around $500. Unfortunately for me, replacing all the fuel injectors and other damage caused by the first mechanic ended up costing almost $1200 - not counting the $400 the first mechanic charged. So, be sure to get a good mechanic to work on your motor and not some low-wage lunkhead hired by a not-reputable dealer.
I would, at the very least, change the oil and oil filter and see if gas is still getting into the oil. If this could simply be the result of extended trolling, then you may need to just take a break from trolling and hammer the motor for a few minutes every now and then to keep the motor up to temp.
Good luck
Edited by Herb_b 5/28/2013 1:46 PM
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