1997 350 Magnum sputters up top (70% throttle or more) - Youtube video inside

[Sheefo2k]

I m using my friend's boat for the summer and so I decided to give it a much needed tune up/TLC.
The boat was rented out 2 years ago to one of his friends and I don't think they did anything but drive the **** out of it and return it at the end of the summer. Last year he went to use it and it overheated instantly. It parked all last summer with a full tank of gas. Fast forward to last month, I got my hands on the boat and right away I took the impeller out and found it in chunks and replaced it. I also did an oil change, new oil filter, new fuel filter and spark plugs. I tested it out for an hour or so and everything was great except when I give it about 60/70% throttle, it bogs BAD and rpms dip up and down. I assumed it was the gas, I removed the gas tank today and drained all the fuel. I added a bout 8 Gallons of 92 Shell gasoline and nothing was resolved except for the better fuel. It only happens when the prop is engaged.

I took the carb out and brought it over to a friend's shop where they took it apart and gave it a quick clean. One thing they told me is that I should get the carb rebuilt if the fresh gas doesn't fix it. The circular cup connected to a spring (in side the carb) was a little dry.

I understand there's a lot more information needed to correctly diagnose this problem (fuel pressure, timing, spark tester) but I was hoping if anyone had a similar situation or knows what I should do next.
When I got home today I removed the air filter and looked inside the carb and saw a puddle of fuel in each corner. I have a feeling it has to do with the carb.

Heres a video to maybe explain things better.

http://www.youtube.com/watch?v=3kD8qr7qvJY&feature=plcp

I don't know much or anything about carbureted engines but I m not mechanically inclined when it comes to FI engines and I m always down to learn something new.

 

[Sheefo2k]

Re: 1997 350 Magnum sputters up top (70% throttle or more) - Youtube video inside

I realized that you can't hear much in the video because of the wind :facepalm: Pretty much it drives fine and then when I give it 60% throttle it takes about a 1 minute until it bogs. If I give it 80% throttle then it will take about 30 seconds before it bogs. If i give it full throttle then it will start to bog after about 5 seconds.

Each time I have to bring the controller back to N and then slowly accelerate.
It sounds as if the carb is flooding up top, or starving, or spark is weak up top... No clue. I m done typing, I ll wait and see what you guys think!

 

[achris]

Re: 1997 350 Magnum sputters up top (70% throttle or more) - Youtube video inside

Sounds like the engine is starving... Did you change the fuel filters? Check them for air leaks too.

 

[tpenfield]

Re: 1997 350 Magnum sputters up top (70% throttle or more) - Youtube video inside

My comments . . .

most engines will idle and rev fine with no load.

I'm also in the fuel supply camp as being the problem. The carb bowl may be gummed up and it cannot get enough fuel into and through it at the high level needed for the higher engine speeds. A full re-build will do the trick, but also a fairly high concentration of carb cleaner may dissolve stuff as well. There have been times when I have run starting fluid through a carb to remove build-up, but that can be too harsh on some of the internal seals, etc.

 

[Sheefo2k]

Re: 1997 350 Magnum sputters up top (70% throttle or more) - Youtube video inside

I don't know much about carbs, how hard would it be to rebuild it? or should I bring it to a pro?
any links or videos to help me rebuild it?

 

[ksukats57]

Re: 1997 350 Magnum sputters up top (70% throttle or more) - Youtube video inside

I had Guaranteed Carburetor do mine because I wasnt confident enough with all the little parts to risk not getting it back together right.


www.flyingfishcarburetors.com

Worked great and was cheaper than local quotes I got.