OMC 350 Planing Issue - Fuel or Prop?

[Chris5280]

Hi Folks-

Thanks to help from several on this forum, I've resolved some of my issues with a 1988 Bayliner Capri 1950 (Rebuilt 350 and OMC Outdrive). Replaced Fuel Pump and Filters to resolve a no-start, then no idle situation.

Now I have a new issue: Boat runs fine and hits 3000/3200 at WOT with my wife and I on board - even pulls a tube just fine at 3000. Add 2 more "normal" size and weight people and she bogs down at 2000ish RPMs and boat will not plane. By moving one person into the cuddy at the front of the boat, she eventually comes down and planes. However, the boat has 6 seats and I feel like she should be able to hit 3500/4000 at WOT even if I had 6 people in seats - never mind 4. I'm assuming I shouldn't have to stick someone in the cuddy to plane

Am I still fighting a fueling issue? If so, where do I look next? Or does this sound more like a prop issue? I never had more than 2 people on board prior to my fuel pump problem, so I have no comparison to know if it's at all related...

Thanks so much guys-

 

[southkogs]

Re: OMC 350 Planing Issue - Fuel or Prop?

When you say "bogs down" do you mean it's struggling to get up on plane (or falling off plane), or do you mean you can hear the engine dying down?

I'm thinking WOT should be over 4000 RPM on your boat. It might be prop issue, but I'd be wondering about things like air/fuel mixture to make sure you're not choking out the engine.

 

[Chris5280]

Re: OMC 350 Planing Issue - Fuel or Prop?

Sorry- by "bogs down" I just meant it can't seem to get enough power to plane unless weight is redistributed.

Would length of fuel line from fuel pump to carb make any difference in adequate fuel supply? The only real change I made was installing about a 3 foot steel fuel line to replace the 2 footer that was stock... (Bought it pre-formed as I didn't have a flare tool...)

Thanks

 

[Maclin]

Re: OMC 350 Planing Issue - Fuel or Prop?

Is this problem new, meaning did it run OK before the fuel pump and filter issues? If it was OK before, what RPM and MPH could you get then?

What speed do you get at the 3200 rpm now?

Gut feel, it Kind of sounds like carb tuning issues or ignition tuning issues. When was the last time the carb was renewed?

Regarding prop, what pitch prop is on there now? Has it always been on there since you got the boat?

 

[wildboater]

I had this problem with a Merc 5.7 260 hp. I had the carb rebuilt. No fix. So, I did my own troubleshooting. It wound up being two ignition parts: The electronic module in the distributor and the coil. The coil didn't show up as a problem until the module was replaced. I replaced the module myself, but had to take it to a marina for the coil since I needed it fixed quickly and no one in town had a coil. The marina water tested the boat and did a couple WOT tests. They discovered the prop was not the proper pitch (yes the coil was bad). I replaced the 3 blade Mirage solid hub (19 pitch) prop with a new four blade stainless 19 pitch. Top speed is about the same, but the holeshot characteristics are different. Trim tabs down, half throttle for the Mirage. Tabs up, quarter throttle to get going then push the throttle as fast as you want.