WOT Issues OMC 5.0 1995

4Wins · Sep 23, 2013

1995 OMC SX COBRA 502APHUE Four Winns 195 Sundowner

I am trouble shooting my engine because I have less than desired WOT speed 3800 RPM and 27 MPH. I also have serious problems planing out under a full boat load.(MPH verified w/ Garmin)
*** I have also noticed that when I am at WOT or in hard turns (heavy load) I am getting a surge and then lag. The RPM's start to increase but quickly begins to decrease again. This happens continuously when I induce it. It creates a back and forth motion. Kinda like if you were pressing your gas pedal in your car very gently and letting off again.***

I have changed:
fuel filter, plugs, wires, cap, and prop. (changed from a 21 pitch to a 19 pitch)
Checked:
butterflies full up and down WOT
Cylinder compression all around 150 psi
Speedometer verified with GARMIN GPS

jerryjerry05 · Sep 24, 2013

Re: WOT Issues OMC 5.0 1995

Could be??
The injectors dirty?
The high pressure pump bad?
The low pressure pump bad?
The vent line from the tank clogged?
This guy had a problem like yours,go to this and read.
http://forums.iboats.com/volvo-pent...tdrives/loss-power-finally-solved-628736.html

alldodge · Sep 24, 2013

Re: WOT Issues OMC 5.0 1995

4Wins said:
*** I have also noticed that when I am at WOT or in hard turns (heavy load) I am getting a surge and then lag. The RPM's start to increase but quickly begins to decrease again. This happens continuously when I induce it. It creates a back and forth motion. Kinda like if you were pressing your gas pedal in your car very gently and letting off again.***

I have changed:
fuel filter, plugs, wires, cap, and prop. (changed from a 21 pitch to a 19 pitch)
Checked:
butterflies full up and down WOT
Cylinder compression all around 150 psi
Speedometer verified with GARMIN GPS

Check your fuel pressure and flow. Sounds like your pump or you carb is the issue.

jerryjerry05 · Sep 25, 2013

Re: WOT Issues OMC 5.0 1995

According to his serial#s.
No carb on this one.

bruceb58 · Sep 26, 2013

Re: WOT Issues OMC 5.0 1995

502APHUE should be a carbed motor. If it was a 502FAPHUE, it would be fuel injection.

4Wins · Sep 26, 2013

Re: WOT Issues OMC 5.0 1995

It is carbed, two barrel Holley.

Walt T · Sep 26, 2013

Re: WOT Issues OMC 5.0 1995

The turns are caused by incorrect float level. All the above by JerryJerry and check that you are getting wide open butterflies with the throttle in full throttle position and looking down the carb to see if the throttle plates in there are wide open. I suggest doing this with the engine off. Another cause can be exhaust flappers if it has them which is not uncommon with boats more than 10 years old. Haven't worked on OMC in years, so someone will chime in if I'm wrong about flappers. I do know they did have them on stringers type at least in the 80s. Coupler slipping is possible but you'd know it by now.

bruceb58 · Sep 26, 2013

Re: WOT Issues OMC 5.0 1995

How old is the fuel?

How long have you had this boat? Has it ever run properly?

jerryjerry05 · Sep 27, 2013

Re: WOT Issues OMC 5.0 1995

Sory about that I guess I missed a letter.
The fuel pump ?
The filters,the fuel lines and the anti-siphon valve at the tank.
The pick up tube in the tank.
The tank vent line.
Timing?Rust in the distributor?

4Wins · Sep 28, 2013

Re: WOT Issues OMC 5.0 1995

Throttle plates are straight up and down with WOT. Gas is fresh 92 octane.

Scott Danforth · Sep 28, 2013

Re: WOT Issues OMC 5.0 1995

is this a new issue? or is the boat new enough to you that it has always been there and your first addressing it now?
When you go into a hard turn, could it be prop cavitation that is unloading the engine?

did this happen prior to you installing the new fuel filter?

you have already checked for full throttle travel.

have you checked the rest of the fuel system?
blocked lines?
plugged filter?
water in fuel?
fuel pressure?

go here and check out threads #8 and 14 http://forums.iboats.com/omc-i-o-inboard-engines-outdrives/adults-only-no-exceptions-468284.html

4Wins · Oct 1, 2013

Re: WOT Issues OMC 5.0 1995

Scott Danforth said:
is this a new issue? or is the boat new enough to you that it has always been there and your first addressing it now?
When you go into a hard turn, could it be prop cavitation that is unloading the engine?

did this happen prior to you installing the new fuel filter?

you have already checked for full throttle travel.

have you checked the rest of the fuel system?
blocked lines?
plugged filter?
water in fuel?
fuel pressure?

go here and check out threads #8 and 14 http://forums.iboats.com/omc-i-o-inboard-engines-outdrives/adults-only-no-exceptions-468284.html

This was happening before but has gotten worse.
This was happening before i replaced the filter.
No blocked lines.
No water in fuel.
Fuel pressure checks good.
Got a mechanic to come out and take a look. Checked fuel pressure and accidentally leaked some fuel on the top of the motor around carb and valve cover. Noticed thousands of tiny air bubbles started to appear up and down the valve cover. Upon removal he noticed the gasket was shot. And there was surface rust the exhaust ports indicating moisture was getting in. Will keep u posted.