Low RPM at WOT

[octave11]

This is similar to thread on here but not the same. I have a 1988 OMC Cobra 5.7 on a Four Winns Horizon 200. Last year i was able to get over 4000 RPM and about 40 MPH at WOT. In the off season it was winterized according to OMC manual. In the spring when i got it ready for summer i put in new spark plugs, fuel filter, thermostat, starter solenoid, and fuel sender. Since then i top out at around 3000 RPM and 30 MPH. I have not changed the prop. The hole shot has also diminished. Is there something i may have done incorrectly that would cause this? Other than this issue the boat runs very well. Thanks

 

[moki]

Re: Low RPM at WOT

On my 88 baretta supersport I found an inline fuel filter inside the carb (where the fuel line connects). Once replaced my rpm issues stopped.

 

[Levinz11]

Re: Low RPM at WOT

When was the last time you did a FULL tune up?

 

[Silvertip]

Re: Low RPM at WOT

You said you installed new plugs! Did you gap them to spec? Did you get a couple of spark plug wires crossed or possibly damage one when you pulled them off the plug? How old is the fuel? Was the fuel stabilized before putting the boat to bed for the winter?

 

[LAC_STS]

Re: Low RPM at WOT

Could be so many things. I would get in there and do a full tune up as Levinz was suggesting. When I had the same problem on my 5.7 it ended up being IGN related. Had to get rid of the resistor wire and add a ballast resistor. But as for your specific case could be anything.


Have you checked if there is water in the fuel? Even with a water sep filter I would check the tank. I would check everything and do a full tune up.

 

[octave11]

Re: Low RPM at WOT

im replacing that today. thanks for reply

 

[octave11]

Re: Low RPM at WOT

good info. thanks for reply

 

[octave11]

Re: Low RPM at WOT

plugs gaped per spec. i have ran at least 5 full tanks through it this summer. fuel stabilized when i winterized. will double check plug wires . thanks.

 

[octave11]

Re: Low RPM at WOT

didn't do it this year. i have been trying to learn how to work on the boat myself. that will be my next step if i cant figure it out with the help of these posts. thanks.

 

[4Wins]

Re: Low RPM at WOT

Have you found the cause to your problem?

 

[octave11]

Re: Low RPM at WOT

Finally took it out again (having very low water levels in our lakes this year). After changing the inline carb filter and and going through the plugs i gained 500 RPM. so now my WOT is 3500 at about 35 MPH on nice flat water with only two people in the boat. im really thinking its a throttle cable issue. to much slack? would that make sense in this situation?

 

[Boomyal]

Re: Low RPM at WOT

Check to see if your butterflies are wide open when you give it full throttle at the helm!

 

[4Wins]

Re: Low RPM at WOT

I am having a very similar issue. Have you found the problem?