50 hp Evinrude bogs down at 4000 rpm

[mfike]

Hi,<br /><br /> I am new to the site and the info is great. I have a 1996 50 hp Evinrude that will bog down as soon as you hit 4000 rpm, and it will not allow the engine to run smoothly unless you get below 2800 rpm. If you kill the engine and restart it you can run anywhere under 4000 rpm and be fine, but as soon as it hits 4000 it bogs down as if it is starved for fuel. The primer bulb is not collapsing but is not very firm either. Priming the bulb as it bogs down does not help either.<br /><br />It has been more consistant as of late but previously it would run great up to 5200 rpm and this would only happen occasionally. We have replaced the fuel line, bulb, power pack, had the tank drained and cleaned, and run carb cleaner in the fuel. What could it be and why wouldn't it be a consistant problem? Any help would be appreciated. Thanks in advance!

 

[Silvertip]

Re: 50 hp Evinrude bogs down at 4000 rpm

Sounds like the engine may be going into SLOW mode which limits engine RPM when a malfunction is detected. Does the alarm system sound when you turn the key from off to run. If not, you may have an overheating problem that is not sounding the alarm. Overheat causes the SLOW mode to limit RPM and will make the engine run rough.

 

[mfike]

Re: 50 hp Evinrude bogs down at 4000 rpm

Thanks for the reply, it does give a short alarm when I turn the key but it has always done that even when it ran well. How can I tell if it is overheating and what can I do to test it?

 

[jmillerz1]

Re: 50 hp Evinrude bogs down at 4000 rpm

I'm in Louisville as well. I haven't found the problem, but was about ready to replace the plugs and fuel filter. Let me know if I can contact you to discuss what I've been doing

 

[Silvertip]

Re: 50 hp Evinrude bogs down at 4000 rpm

The alarm is supposed to chirp when the key is turned to the RUN position. Thats the signal that the horn is working. Check the overheat circuit by disconnecting the brown wire near the temp sensor on the head. Ground the wire (not the sensor end) to the block. The horn should sound. If it does, that part of the system is apparently working. Try leaving that wire disonnected and make a quick run to 4000 RPM and see if it bogs. If it does, try pushing in on the key (choke/primer) momentarily. If the engine picks up, its a fuel delivery problem. Probably a fuel pump getting weak. Also look at the primer bulb when the failure is going on. If its sucked flat, there is a fuel restriction ahead of the bulb. (Tank pickup, bad bulb, pinched line, etc.). If the choke/primer doesn't help, then ignition and carbs need to be investigated. It is still possible that the SLOW mode is being activated due to an internal power pack problem (regardless whether its overheating or not). 2500 - 2800 is about the range that mode kicks in. It may be time for a power pack but do the cheap things first.

 

[mfike]

Re: 50 hp Evinrude bogs down at 4000 rpm

Upinsmoke,<br /><br /> Thanks for the reply, the power pack was the first thing replaced when it was summerized. The mechanic (I use the term loosley) said it was running on one cylinder, but I think it was the same issue I am finding now. I will definatly try disconnecting the temp sensor. The bulb has never been firm even after we replaced it and the fuel filter is never full. I have held in the choke because I thought that it may be getting stuck in the on position and it does not increase the performance of the engine. The bulb will not get firm even when it is not running. Thanks for your help.