1999 Yamaha 100hp 4 stroke Stalls

[mmarcom1]

I just bought a houseboat with a 100hp 4 stroke with 198 hours on it. The engine has always run great (I know the boat), until this year. The owner hadn't started it in 3-4 months and it wouldn't rev up and idled rough. He had a local reputable marine tech come out and look at it. He said the carbs were dirty and had water in them. He took them off, back to his shop, and cleaned them. He reinstalled them and it runs great. Here's the problem. It runs great until I try to dock it back in the slip, then it decides to stall. I let it run for several minutes to warm up, backed out of the slip and headed out of the marina. The whole time it is running great, smooth as silk. I go out to the entrance of the marina and head back in. (I am trying to learn how to park this 45 foot beast) I get within 40 feet of the dock and it stalls. It seems to do it when I am easing into the dock. It's a big boat so I have to shift into forward and bump the throttle, shift back to neutral, back to forward and bump, back to neutral, into reverse and bump, you get the picture. It's a finesse thing with a boat this big especially with the wind blowing. Anyway, during all of this it stalls. I can start it back up and it may stall immediately or after shifting into gear and moving the throttle. I can take it back out and it runs fine. I even did this whole bump and shift thing out in the open and it did fine until I got back within 30-40 feet of the dock. It always seems to do it either right after bumping the throttle and pulling back to idle, or when shifting from forward to reverse or the opposite. When I say I'm bumping the throttle, I am talking about shifting into gear and bumping a quick 1500-2000 rpms and back to idle just for a little reaction from the boat. With the boat being this size, you can't make big moves that close to the dock, it takes too long to correct it when it's out of shape. Any ideas what this might be? The tech is supposed to be going back out to look at it but I don't know how he will see it mess up without driving it.

[boats.net]

The tech probably needs to recheck carb sync.

[99yam40]

Something to think about is where the water in carbs came from,
tank and all lines along with filters need to be clean of water and old fuel.

Hopefully the fuel was not ethanol and was treated when fresh before sitting that long

[mmarcom1]

The old tank had water in it. The tank has been replaced with a new one, water seperater has been replaced, I think the fuel filter has been replaced. I know the tech cleaned the carbs and said there was water in them. It barely ran before and runs great now other than stalling when it doesn't need to. It takes the gas when you rev it up even in gear I had it up to 2800 rpm under load and back to idle with no stalling when going out of the marina. It has to be something with a mixture screw, float, or an issue with the carbs not being in sync. The tech is supposed to go back out this week. I will keep you posted.

[mmarcom1]

Just a follow-up for you guys. Tech removed fuel pumps, tested good, no leaks. Took them apart and they had crud in them. He cleaned them and reinstalled. Motor still stalling. Replaced pumps, no more stalling, but started sputtering at higher RPM's. Found crud from the fuel pumps had gotten back into the carbs after initial cleaning of carbs. Removed and cleaned carbs, reinstalled. All is well so far.