Running engine on muffs.

[bailey05]

I have a question regarding running the engine on muffs. The engine is a Yamaha 250HP 4- stroke. Every time I try to run the engine on muffs I can’t get water to exit the tell-tale hole. I typically let the engine run for about 30 – 40 seconds because I am afraid to let the engine run longer for fear of ruining the impeller. I am using the split muffs that feed water on both sides and I believe the water pressure is adequate. Do I need to let the engine run longer? When the Yamaha service tech services the engine, he gets water to flow from the tell-tale but I don’t know how long he was running the engine.

[boats.net]

I personally don't trust the muffs, have seen a lot of water pumps damaged from using them. Some model F250 have dual water pickup on gearcase and if you have one of those models then would need muffs for both pickup areas to supply enough water to water pump. The muffs have to fit tight on gearcase, if see a lot of water spraying out around rubber cups then may not be getting enough water to pump.

[Joe Chatham]

Muffs and freshwater flush

I have twin 2005 4 strokes and I use one hose connected to the muffs and also attach a hose to the freshwater flush connection. Running both at the same time worked fine. This is what a Yamaha tech told me to do. He said using the muffs alone would not supply enough volume.

[phonfish]

Running on muffs

I tried using the 2 sided muffs on my twin f`150s. burnt up the impellers. Went to dealer (Bills Marine in Portsmouth Va) and asked what they use when servicing yamahas. He uses a cheap one sided muff and duct tapes the ears in place so they wont slip off while servicing.
Now when I use the single sided muff, I can get it to pee.

[davepjr71]

I ran into this problem today. Double muffs and no water out spout. I had to push in on muffs to get it to work. I should take the doubles back and get the single and duct tape that sucker on.