Need Help On Boat Throttle Issue

Discussion in 'Boats and Motors' started by Knopper76, Aug 6, 2008.

  1. Hey guys got a question for you mechanically inclined. A buddy is having an issue with his boat. When running it full throttle it goes fine for a bit and then all off a sudden it's like it bogs down and almost cuts out. Will do this for a few seconds then kick back up. Or sometimes when he is running 3/4 full then goes to full it does the same thing. It almost seems like maybe it is flooding out then burning the gas off then kicking back in. I don't know and we are at our wits end trying to figure it out. Perhaps he is gonna have to take it in to have it looed at. But thought I would check here for ideas. Thanks in advance.
  2. Make, year, and HP motor?

  3. KaGee

    KaGee Monkeywrench Staff Member

    Sounds like fuel starvation.
  4. Merc cruiser 4.3LX, 205 hp, 1988 he believes
  5. yea sounds more to me like a fuel issue. whether the pickup isn't getting fed, or pump is failing. line could just be kinked, but doubtful if you're getting good response and then just shutting down randomly.
  6. yeah getting good initial response. Like from start to ful throttle no problems at all, just when your going full throttle for a few it starts to bog down then does completely...then picks back up when you throttle back then go full. Thanks for the coments guys.
  7. KaGee

    KaGee Monkeywrench Staff Member

    When was the last time the filters were inspected or changed? Engine tuned up?

    There is a clear tube from the fuel pump to the carb... inspect for signs of fuel. If there is fuel in the tube, the fuel pump is going bad.

    Other than that, the correct procedure is to hook up a pressure gauge and see what the fuel pressure looks like when the symptoms occur. Or take it to an mechanic.
  8. i just had wwhat sounds like the same issue.i would be running at about 1/2 to 3/4 throttle and the engine would just up and spitting or sputtering just die.would come to a stop wait a few seconds and would start right back up with no hesitation.the engine was tuned up new everything that would be in a tune would only do this at random and only at about half throttle. i eventually found out that i had water in the carb. i poured a couple of bottles of heet in the tank and as of now it seems to have taken care of the issue. when my fuel pump went out it messed up all the time except at idle.
  9. A plugged or not fully opened gas tank vent cap will cause a similar thing.
  10. UFM82

    UFM82 The one others want to be

    1) Fuel vent blocked. Check the tank vent and run a fine wire back through the line. Spiders, wasps and other creatures like to make homes in there and block things off. A sure way to diagnose is to have the boat do it's thing and immediately unscrew the fuel cap. If it makes a big sucking sound it's a clogged vent.

    2) Carb blockage. The carbs on boats sit for long periods of time and then get run. Then they sit. The fuel evaporates out of the bowls and leaves residue. After time, it builds up and causes problems. Under high fuel flow the dirt is sucked into the jets and blocks the flow. Then the fuel demand drops when the engine stalls or sputters and the dirt falls free. Then the fuel demand picks up again and on and on. The only way to fix the issue is to remove the carb and thoroughly clean it, spraying cleaner and then compressed air through ALL the galleys in the body. Replace any necessary parts and all gaskets and reinstall.

    3) Water in the fuel. While this could cause the issue, water usually causes hard starts and rough running and sometimes lowered WOT. If the boat has a water-separating filter on it, change it at the beginning of each season as condensation can cause water build-up in the tank. If the filter is a simple filter, replace it with a water-separator. Most I/O's I've seen use a water filter so it may already be there.

    4) Fuel pumps normally go kaput and die but if the diaphragm has pinhole, it could result in a fuel starvation issue. As stated above, look for fuel in the drain tube from the fuel pump. That's a sure sign of a ruptured diaphragm. I've replaced a multiude of pumps over the years and most show leaks before actually dying but many never exhibited any running issues.

  11. Seaturd

    Seaturd Catcher of Fish

    Sounds like a fuel starvation issue to me - replace filters first. Carb may have screen filter on fuel line leading into it.
  12. Hey guys I appreciate all the feed back. The fuel filter is new, but we will check into the carb, and fuel pump ideas. Thanks again knew I could count on fellow OGF'ers to help us out. I will keep you posted on what we find out was the culprit.
  13. Hey guys just an update. Turned out to be the carb, took her apart gave her a nice bath and buttoned it all up, and she started and ran like a dream. No bogging down or anything. So thanks again for all you replys.