RPM not reached at WOT

[cheers731]

The 92 OMC 5.8L/Cobra is doing something weird and need some troubleshooting. I post a thread a week ago about engine rattle at 1500 rpm prop engaged running on the leftover fuel from winter storage. Took the boat out yesterday with fresh gas and boat start up much easier, idled smoothly and no rattle/vibration at 1500rpm. Once out of no-wake zone hit the WOT and the boat won't plane. I thought the trim was not down all the way so adjust the trim and boat ran nicely. After that, did boating with low or high rpm for about 6 hrs and it was great until on my way back to dock. I hit the WOT and it stayed at 3000rpm and boat won't plane. Perhaps the normal 4200rpm at WOT not reached because the boat was not planed. Boat has 4 adults in it and was planning at 2500 rpm a couple hours ago. I read through the #13 on adults only but wondering what could cause this intermittent weak power problem?
Thanks for your advice.
Frank

 

[Howard Sterndrive]

Re: RPM not reached at WOT

ESA is the only thing not on the list in the adults only that comes to mind as possible intermittent.

linkage to the carb is a good place to start - and checking that the choke plate isn't closing - some basic visual checks while someone else drives - watch the ESA switches while someone shifts (in the lake).

I'm pretty quick to check voltage to the coil + terminal in diagnosing problems like that...

 

[cheers731]

Re: RPM not reached at WOT

Thank you so much, really really appreciate your advice.

 

[HT32BSX115]

Re: RPM not reached at WOT

92 OMC 5.8L/Cobra

Howdy,


You might be a little more specific on what you have.........like model number. Some 92 model Cobras used electronic ignition and had the cone-clutch drive for example. (so NO ESA)

After you change filters, replace fuel with fresh, ensure that your in-tank fuel pickup and fuel vent are not partially blocked, you should check timing and other ignition issues.

Having said all that, when i had a WOT RPM issue with my previously installed OMC 460, after checking EVERYTHING, ..............I discovered that it had several flat lobes on the camshaft.


Regards,


Rick

 

[cheers731]

Re: RPM not reached at WOT

Sorry, my bad. It is a 92 Four Winns 205 Sumdowner. It has OMC 5.8L engine with Ford stamped on it and a Cobra outdrive. It has a Holley 2 barrels carb and does have a ESA on it. I am not sure if it has a fuel filter but it has a fuel water separator. It has not been changed since I have the boat for 2 years. I will have it changed tomorrow then do a test run on Tue and report back. One thing I did today is to clean the fire arrestor. While I checking around the linkage and wires, I noticed the flame arrestor is very dirty. No light can go through, looks like it has never been cleaned. I hope it will make a difference. I will report back on Tue.
Can't say enough thanks for your advices.

 

[HT32BSX115]

Re: RPM not reached at WOT

Sorry, my bad................fuel water separator. It has not been changed since I have the boat for 2 years. I will have it changed tomorrow then do a test run on Tue and report back. One thing I did today is to clean the fire arrestor.

No problem!

The fuel/water separator IS the fuel filter! Start there. It's unlikely the flame arrester is plugged bad enough to restrict airflow but you should be able to see through it....


Hope the filter change fixes it!

 

[cheers731]

Re: RPM not reached at WOT

Bad news.
Got the fuel filter changed yesterday and started athe engine at curb side, it ran well for 2 min then I turn off the engine. Took it to the lake around noon, it ran very well, plan quickly and I ran it at 3500 rpm for about 5 min then slow down to idle. Tried take off again and it won't plan, feels like engine does not have full power. Check the engine temp and oil, they are fine, but now I doubt the temp guage is showing correctly because engine is showing some signs of overheating. Engine has a fresh water cooling system and the heat exchanger is very hot. The lower big hose is very hot but all other hoses are cold. I used to hear some grinding noise once a while but it always goes away, does it suggest the water pump is failing?
I quickly turn back toward launch ramp and use idle speed going back. The temperature goes in between 150 to 190 has not go beyond 190. I have my helper drive the boat and I paddled the boat hoping it will reduce the use of engine. Finally, I got the boat on the trailer but feel sad on what I have done. I alway feel the temp on heat exchanger and risers and they always warn, never hot until now. I don't know how much damage I have done but guess a cylinder compression test will be the next. Please advise me on what else I should check, and is it a failing pump or I have a obstruction on returning hose from heat exchanger?