Evinrude 40HP loss of power after 30 mins. running

[monoshock]

Hello, this is my first post. I have a problem with my 1991 Evinrude 40HP ,after it runs fine for about 30 mins. it starts to lose power and cuts out. It does'nt stop but has about 1/4 power. I can push the chock/enrichment on the key and it will run fine for a short burst about 5-10 seconds. I have replaced the fuel line from the tank,checked the tank vent,took the carbs off and cleaned them-the jets are all clean,changed the spark plugs several times, installed a new coil. I think the problem is fuel related. I'm running a electric fuel pump and have been for two years with no problems, but I did installed a new fuel pump. This problem just started this season. I've checked everything I know and can't fix it. Anyone have a idea, I need the help. Or maybe I could just take shorter trips, LOL.

 

[CATransplant]

Re: Evinrude 40HP loss of power after 30 mins. running

OK, what has changed? You installed a new fuel pump. I'm assuming here that you switched to an electric fuel pump for some reason, but we won't get into that, because you had one before and everything worked fine. <br /><br />Where is the fuel pump located? Is it an identical pump with the one you had before.<br /><br />You're right that this sounds like a fuel problem. Heat may be playing a role in this, too. Try swapping out the fuel pump and see if that takes care of the problem.

 

[angus63]

Re: Evinrude 40HP loss of power after 30 mins. running

Welcome Mono<br />You can start by using a remote tank and different fuel line and bulb (borrow one?) to prove out if it is fuel tank or fuel delivery to the motor. Does the problem go away after immediately restarting? Does it go away after cool down? Does it happen when the fuel tank is full, 1/2 , 1/4? Have you checked every fuel connection for leaks?<br />Good luck

 

[monoshock]

Re: Evinrude 40HP loss of power after 30 mins. running

Hello, I changed the fuel pump with the same make and model as the old one; as a matter of fact I have changed it with two different new ones to make sure that wasn’t the problem. I have pulled in shallow water (when the problem has happened) unhooked the fuel line and pumped fuel back in to the tank to check the fuel flow and everything is fine. I have also bought a 6 gal. Portable tank and it has the same problem with this tank. I’ve check all the fuel lines for leaks or holes, they all look fine. When I had the carbs. off I used a small light and looked at the reed valves they look good. I have worked on 2 cycles (dirt bikes, and outboards) for years, this one has me stumped.

 

[CATransplant]

Re: Evinrude 40HP loss of power after 30 mins. running

Hmm..is the outboard pumping water OK? I suppose this could be an overheating problem or something else. But, the fact that it runs better when you hit the choke/enrichment after it stalls militates against both of those, although I suppose it might help in an overheating situation a little.

 

[monoshock]

Re: Evinrude 40HP loss of power after 30 mins. running

I installed a new impeller at the start of the season. Its pumping water fine. I also tryed unpluging the brown SLOW wire from the sensor, this didn’t help.

 

[monoshock]

Re: Evinrude 40HP loss of power after 30 mins. running

Originally posted by monoshock:<br /> Hello, this is my first post. I have a problem with my 1991 Evinrude 40HP ,after it runs fine for about 30 mins. it starts to lose power and cuts out. It does'nt stop but has about 1/4 power. I can push the chock/enrichment on the key and it will run fine for a short burst about 5-10 seconds. I have replaced the fuel line from the tank,checked the tank vent,took the carbs off and cleaned them-the jets are all clean,changed the spark plugs several times, installed a new coil. I think the problem is fuel related. I'm running a electric fuel pump and have been for two years with no problems, but I did installed a new fuel pump. This problem just started this season. I've checked everything I know and can't fix it. Anyone have a idea, I need the help. Or maybe I could just take shorter trips, LOL.

Hope someone can help on this problem.

 

[itstippy]

Re: Evinrude 40HP loss of power after 30 mins. running

That's weird that it will run for 30 minutes before acting up. I'd think heat or fuel issues would show up quicker than that; as soon as it's up to (or beyond) temp or had time to create a vacuum somewhere in the fuel system. Say ten minutes.<br />As Angus63 asked, does shutting it down and quickly restarting have any effect after it's acting up? Removing the cowl? Pulling plug wires one at a time? Can you lay your hand on the head? The guys on this site will figure it out if you give them enough info.

 

[monoshock]

Re: Evinrude 40HP loss of power after 30 mins. running

Thanks for your reply. When the problem happens, I have let it cool off with the cover off for 30 min to one hour, after restart it has the same problem. So I will start back to the ramp pushing the key in about every 5-6 seconds and load it up for the trip home. Most of the time I will work on it with the (Lake on a Hose) hooked up and try to find what's wrong. The next time I put it in the water, runs fine for 30min and the same thing happens. I've been working on this for 2 months now. I'm thinking maybe a gasket on the intake side could be developing a leak after the motor reaches operating temp.I'm a very stubborn (and cheap) person and like to find a problem instead of just paying someone else to fix it.

 

[monoshock]

Re: Evinrude 40HP loss of power after 30 mins. running

Also the motor tempature doesn't seem to be hot like it's over heating. I have pulled the wires, both plugs a firing. I'm sure it a fuel problem but can't figure it out. I'm sure someone must of had this problem before.

 

[foxster]

Re: Evinrude 40HP loss of power after 30 mins. running

Check your connections on hose end comming from tank and check where it hooks on to the connection at the motor.I remember a problem something like this once,and everything had been checked three times over and had been determined that the problem was for sure related well it turned out,that the Female connections on both ends of the hose,has a rubber-o-ring in them,it would seal when pluged in but as the boat bounced accross the water the vibration from just normal use would losen these connections ( even though they were still locked in and looking good)and cause an air leak.If I remember right the guy who had this problem had changed 3/4 of his electrical system and rebuilt the entire fuel system.Kind of an expensive lesson to find out the whole problem lyed in a $2.00 part you can find at a Wal-mart.Just a thought but you might want to give this a check.He also thought he had his problem traced down to an exact time.Good Luck

 

[monoshock]

Re: Evinrude 40HP loss of power after 30 mins. running

Thanks, I was thinking of the o-rings when I was doing the flow test on the water, thinking maybe they were losing the seal in motion. I'll try new ends and see if it helps.

 

[Jcrain]

Re: Evinrude 40HP loss of power after 30 mins. running

I know this might sound odd, but have you rerouted the fuel lines? Could it be a bit of vapor lock?

 

[monoshock]

Re: Evinrude 40HP loss of power after 30 mins. running

Hello, I haven't rerouted the internal lines, just the external lines and mounted the electric fuel pump about 2 1/2 years ago. I removed the VRO pump and have been running premix 50:1.

 

[monoshock]

Re: Evinrude 40HP loss of power after 30 mins. running

Hello, I've been working on the 40hp all afternoon about 3-4 hours. I was thinking it could be the CDI unit under the flywheel, has anyone had problems with this before. Do they just work or not work?

 

[monoshock]

Re: Evinrude 40HP loss of power after 30 mins. running

I for got to say, I did a compression check, 125psi and 127psi looks OK to me.

 

[monoshock]

Re: Evinrude 40HP loss of power after 30 mins. running

Hello, hope someone can help with this problem. Does anyone think It could be a falty CDI unit?

 

[chpowell]

Re: Evinrude 40HP loss of power after 30 mins. running

I had the same problem a couple years ago with my 50hp Evinrude, Turned out it was the thermostat. It was sticking open and over cooling the engine.

 

[monoshock]

Re: Evinrude 40HP loss of power after 30 mins. running

Thanks for the input. I worked on the motor yesterday again, cleaned the carbs,changed the fuel lines, changed the spark plugs, it sounds good on the water hose but didn't get to take it to the water yet. I think I will get a new thermostat before the next test run, I think the temp does seem low to me so mabe it will help. Thanks - chpowell

 

[monoshock]

Re: Evinrude 40HP loss of power after 30 mins. running

We took the old 14ft Sears alum. w/74 25HP Johnson out yesterday, that old motor will run for ever just keep gas and oil in it, sometime high tech is a pain in the rear.