'93 OMC 351 hesitation/miss around 3400 RPM

[firefighter4u]

Boat is new to me and I'm experiencing a hesitation/miss around 3400 RPM both during acceleration and deceleration. Engine does not hesitate below or above that RPM. So far I have changed the fuel filter (yes there was water in it - drained tank, treated and filled with new) and changed the spark plugs, rotor, distributor cap and coil. Mechanic said carburetor is fine. Plug wires are next on my list to do, but I'm baffled what else the problem could be. Perhaps the distributor itself (spitfire) is having issues? I'm also appearing to have an issue with my alternator not charging my batteries thoroughly. Volt meter on dash only reads 11 and batteries are going dead. I metered the batteries (relatively new batteries) with engine running at idle and higher RPM and they read about 12 - 12.5 - that doesn't seem high enough. Any thoughts? The model number on the engine is 584DPPJVB

 

[kenny nunez]

Check that there is voltage at the alternator out put stud. There could be a fusible link that is burned. Someone may have connected the battery backwards. If there is voltage take the alternator to a rebuild shop and have it load tested.

 

[firefighter4u]

So I ended up buying a new alternator. Put it in this weekend and sure enough, the hesitation at 3400 RPM was gone! Runs like a champ. However, I still find it odd that at idle or slightly above the volt meter still reads about 11 volts. at high RPM it goes up to about 12.5 - 13. is that enough to charge the batteries without having to run up and down the lake? Next year I hope to have a slip at the dock with shore power. I'm just glad that hesitation is gone, drove me nuts.

 

[kenny nunez]

If you are running the boat with both batteries switched together that may be the reason for only going to 13 volts. Especially if one battery is not as good as the other and will cause an imbalance. Have both batteries load tested after having them trickle charged for 24 hours separately.

 

[firefighter4u]

ok, I'll do that. I know they are grounded together but their positive cables are separate. I have a battery switch which I have been selecting both to start the boat but then switch it to the battery that has less juice to try and charge it. I was looking at solar powered trickle chargers that would help keep the battery charged during the week. Thanks for the info.