OMC 5.0 Stumbling issues

Hey fellas I've been chasing this problem for a while now. and haven't had any luck yet. The Boat has a 1990 OMC 5.0. The issue is when I go to WOT the boat stumbles and spudders. sometimes it will run great and then some times the problem pops up. it pops up more than runs great .It also runs awesome on the ear muffs in the drive way purrs like a kitten. I've went through the carb"2 barrel" Holly with a rebuild kit and even after the rebuild I've went back to make sure the jets were clean. I've also replaced the fuel filter and ignition coil and spark plugs. I'm kind of stumped I'm trying to get the boat ready for this weekend but not all that excited with this issue. I've read that it might be the pick up line being clogged in the gas tank. This might explain why it took about 3-4 min of turning over the motor to prime the new fuel filter and to get the motor fired up. or it might be electrical in the dis cap. any thoughts on this?

Also what is the normal operating RPM for a OMC 5.0 with a Cobra outdrive? all I can get out of it is around 32-3400 rpm and maybe 35-40MPH does this sound about right?

Thanks in advance! hopefully I will get this all knocked out and working properly.

Re: OMC 5.0 Stumbling issues

Accelerator pump in the carb, or timing. Is the boat new to you?

Re: OMC 5.0 Stumbling issues

KlrPanda said:

Hey fellas I've been chasing this problem for a while now. and haven't had any luck yet. The Boat has a 1990 OMC 5.0. The issue is when I go to WOT the boat stumbles and spudders. sometimes it will run great and then some times the problem pops up. it pops up more than runs great .It also runs awesome on the ear muffs in the drive way purrs like a kitten. I've went through the carb"2 barrel" Holly with a rebuild kit and even after the rebuild I've went back to make sure the jets were clean. I've also replaced the fuel filter and ignition coil and spark plugs. I'm kind of stumped I'm trying to get the boat ready for this weekend but not all that excited with this issue. I've read that it might be the pick up line being clogged in the gas tank. This might explain why it took about 3-4 min of turning over the motor to prime the new fuel filter and to get the motor fired up. or it might be electrical in the dis cap. any thoughts on this?

Also what is the normal operating RPM for a OMC 5.0 with a Cobra outdrive? all I can get out of it is around 32-3400 rpm and maybe 35-40MPH does this sound about right?

Thanks in advance! hopefully I will get this all knocked out and working properly.

Click to expand...

Ayuh,... Sounds like it's down on power, or the prop is too Big,...

Ya should be turnin' 4400/ 4600 rpms, at Wot...

Re: OMC 5.0 Stumbling issues

Bond-o said:

Ayuh,... Sounds like it's down on power, or the prop is too Big,...

Ya should be turnin' 4400/ 4600 rpms, at Wot...

Click to expand...

Sounds to me like a electrical problem with the cap or plug wires, These can operate ok under lite load, but under heavy lead the spark can break down and cause the engine to not fully rev up.

Re: OMC 5.0 Stumbling issues

617bsman said:

Sounds to me like a electrical problem with the cap or plug wires, These can operate ok under lite load, but under heavy lead the spark can break down and cause the engine to not fully rev up.

Click to expand...

The boat is new to me.. I timed the boat yesterday it has 9-10* at idle and right around 28* at WOT... I also replaced a few vacuume lines that were dirty. I'm going to take it Out on the lake this weekend and see how it acts. I also cleaned the cap going to replace plug wires and dis cap. If its not fixed with the timing.

Re: OMC 5.0 Stumbling issues

If you have an electric fuel pump check that it’s working correctly example electrical connection and fuel pressure, it may be starving for fuel at high RPM's