1999 yamaha f80 gas in crancase oil

R

reelchef

New member
Hi All,
My 1999 f80 lost power about a week ago. I flipped it around and crept back to the dock. I checked plugs, top plug running too rich, all carboned up. I then checked oil, and upon removing dipstick, oil/gas mixture shot out. I inspected my hoses and found a good sized tear in the tiny hose leading to one of the fuel pumps. I suspect that the diaphragm in pump was ripped due to air leak, and was dumping gas. Does this sound about right? The carbs were rebuilt 2 years ago, and ran fine for the last 100 hrs I have had the boat, so I don't think it is a stuck float. Any input or owners with similar problems/outcomes would be appreciated.
 
I had a yamaha 100 that had a fuel pump failure where a spring broke and the baklite body broke within the pump allowing fuel to get past an o-ring on the push rod that is driven by the cam. That does dump fuel into the oil. You can take the pump apart and check for damage. However, an extremely rich mixture in a carb can dump unburned fuel past the rings into the crankcase. I would check both items, and change oil and filter.
 
Most non electric pumps run off a cam shaft and there will be a diaphragm which the lever to the pump goes thru--if this ruptures, then fuel into the oil. No harm, but you have to change the oil and spring for a new pump. In this case it sounds as if new plugs, and a decarb are in order. Go from there.
 
Thank You both. New Pumps already ordered, hopefully here by Monday. I will change the plugs and oil before I fire it up. Only 6 weeks left here in our NY season, before the marina closes....I would love to end on a good running note.
 
Hi All- I took apart both fuel pumps. The top diaphragm was ripped. I then removed other fuel pump, inspected and is fine. I replaced bad fuel pump, de- carbed with seafoam spray, changed plugs and oil. I took her out and she ran great!!! Thank you all for your assistance, I feel like I won a round only spending 200 bucks online, as opposed to paying the Yamaha reaper(dealer). This job would have probably been $800 or so.....
 
Thism same thing happened to me about a month ago. I was going to take the boat up to Sportcraft for the yearly service on the twin hondas but wanted one more trip to the coast. The night before leavihg pulled the covers and pulled a dipstick and oil/gas shot out. Sportcraft changed out both pumps and both thermostats as they all looked bad. New zincs, the works. In doing this they also checked for a slight ticking I thought I could hear the last time I used the boat. Seems it was coming from the flywheel area. They pulled the flywheel and found that the magnets were coming loose, and one had jumped around and wedged behind one of the others. Flywheels are rather expensive, but they said they had never seen one fail before. Now going to wait for spring to try it out.
 
Back
Top