1984 evinrude 6hp dropping power while full throttle

kevinstan

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I have a 1984 evinrude 6hp. At the lake last weekend while running full throttle it started dropping power like it was not getting gas. I could only run it at a medium speed to get back to the dock and take it out. It wouldn't run wide open at all without bogging down. I just rebuilt the carb 2 weeks ago so I cannot figure out what is wrong. The fuel tank and hose and primer bulb are all old so I have purchased new tank hose bulb and everything which I will be replacing this weekend. But what else could cause this type of issue ? I noticed with the portable fuel tank in the back bottom floor of the boat it wouldn't even start. I had to set the tank up in the seat to even get it started. Could it just be the old fuel tank and hoses and connectors ?
 

lindy46

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Weak/failing fuel pump? Will it run wide open if you continuously squeeze the primer bulb? Has it been running good at all since you rebuilt the carb?
 

kevinstan

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Fuel pump is new. I replaced that when I got te engine. Primer bulb stays tight once primed so I couldn't continue to squeeze it. That was the first time out since I rebuilt the carb but in ran at home in the trash can filled with water really good before I took it out. Before carb rebuild it wouldn't hardly start or run at all. Seems like the carb rebuild fixed that issue but now this.
 

sutor623

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I would get some clear vinyl hose from lowes and put it in line after the fuel pump to the carb. If you see lots of air bubbles coming through then you have an air leak somewhere.

Maybe you are dropping a cylinder? I have had a few 4hp's of that era, and it seemed that I had to be really careful not to contact the lower sparkplug wire with the engine cover latch when putting the hood back on.
 
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kevinstan

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I will try the clean fuel line and check for bubbles. What would be a cause of air getting in ? The old fuel tank and hoses ? I am just wondering since I have the replacement for all of that. Maybe that could be a fix ?
 

sutor623

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I will try the clean fuel line and check for bubbles. What would be a cause of air getting in ? The old fuel tank and hoses ? I am just wondering since I have the replacement for all of that. Maybe that could be a fix ?


May fix it. Typically if you have a leak BEFORE the fuel pump, you will have fuel leaking from that fitting. If you can get it to try and start better by lifting the fuel tank, that tells us that you have an issue getting fuel to the motor when fighting gravity.

Did the motor run at all after you rebuilt the carb? Did you use a new carb kit?

Do you have an inline fuel filter? If so did you check/change it? If you dont have one you really should add one.

In the future, do not bother rebuilding the carb if you arent going to change old dirty fuel lines, fuel bulbs, fittings and filters FIRST. It is easy to take those little (Expensive) pumps off and check the inlet. Those fuel pumps are small. It sounds to me like you got some debris in the entry to the fuel pump. Especially since you didn't clean up the fuel system BEFORE the carb when doing the carb. Kind of like washing the bottom of the car first.

If you still have the old fuel pump perhaps you can swap it out for the new one and see how she does.
 
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kevinstan

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That was the first time I took it out after rebuilding the carb. And yes it was a new carb rebuild kit. Also yes there is an inline fuel filter. I will replace all of that with the new tank and hoses and primer bulb. Can I just clean the inline filter and reuse it ? It's clear and has a metal screen inside it. Or do I need a new one ?
 

OptsyEagle

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Usually if you are having a fuel pumping problem the motor will simply run out of gas. All the fuel pumping apparatus does is get fuel to the carburetor bowl. You will either have fuel in there or not. If you do, you should be able to run the motor fast, slow or medium throttle right up until the gas is gone. When you have a running motor that seems to idle OK but has little top end power, you usually have a motor running on only one cylinder. So time for a cylinder drop test.

Start up the motor, let it warm up and bring it to a fast idle. With a pair of insulated pliers, pull one spark plug boot at a time. These motors should be able to run very well on one cylinder albeit at a highly reduced power at the top end. If the motor dies on you when you pull a plug boot, then you know that the other cylinder was never firing or was very weak.

Now the issue of the motor not starting unless you hold the fuel tank above the motor seems like a separate issue to me and a fuel pumping issue. Since you said you had some new fuel tank parts coming, I would see how things work after that. As for the clear fuel hose. Gas usually has some air bubbles in it when things are running fine so the observation of air bubbles will probably tell you very little. Now if you see no gas moving at all, that will tell you something but you can observe that better by removing the line connection to the carb and pulling the starter cord and see if fuel is pumping or not.
 
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kevinstan

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I will try the cylinder drop test and post the results shorty. Also still going to try the clear fuel hose just to check things out. Will I be able to reuse my inline fuel filter or should I replace it ? The one on there now is red plastic and has a fine metal mesh screen inside it. I was gonna flush it with water and reuse it if possible. ?
 

sutor623

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I wouldn't flush it with water. If you didn't change that filter, yet cleaned out the carbs.......... Catch my drift?

What was the issue before you cleaned the carb, was it the same issue? If so, like OE said, probably a spark issue.
 

kevinstan

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Here's the full story - and maybe this will help everyone be able to help me better: When I purchased the boat the previous owner started the motor for me and it seemed to start right up with no problem. Even after I got the boat home I tested it myself a few times through the week and it would seem to start and run without any issues. A week later I took it o the lake and got it in the water and it didn't even want to start. After continuously trying it finally fired up but would only run at about half speed even with full throttle. I would also have to halfway choke it for it to stay running. I knew the previous owner told me he never cleaned the carb or rebuilt it in the 2 years he owned it so I assumed it needed to be done. I purchased a new carb rebuild kit and did it in a few hours. Started right up first pull after that and sounded great. Sounded like it had much more power than before. With my new confidence level after rebuilding the carb I took it back to the lake this past weekend, launched the boat and got in and pulled the pull cord and nothing. Wouldn't start. I realized that at home I had the fuel tank in the seat instead of on the floor, so once I moved the tank to the seat beside me and after a few more pulls of the rope, it started up. I stayed close to the dock but wanted to ride around a bit, and while at full throttle it would all of a sudden drop power then kick back up, then drop power again or sound like it was about to die. I noticed if I throttled down to a medium speed it would go without a problem at a steady pace, but on full throttle it would seem ok for a minute, then drop then rev, then drop then rev. I figured since the fuel tank is so old it has turned yellow, and the no telling how old the hoses were - I decided to purchase a new fuel tank, new primer bulb, and new connectors for everything. I was assuming maybe between the old fuel tank and hoses and connectors maybe air was getting in, or the tank hose inside the tank could be giving out or getting clogged or any of the other hoses so that's where I decided to start. Funny thing is that back at home in the trash can of water it will start and run perfectly fine. Seems like it's just in the lake or probably in drive at full throttle. I hope some of that maybe helped a little more. I just want to have a plan B if it's not the tank and hoses. I am also going to open the fuel pump and clean the screen then replace all the hoses and fuel line.
 

kevinstan

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Tim: I do have a water pump kit that I have not put on yet. Could that cause an issue like this ? At very low idle no water comes out but once I give it just a little throttle then water starts out the pee hole and all seems fine. Since I have no idea when it was replaced last I got a new water pump kit and plan on changing it soon.
 

sutor623

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Tim: I do have a water pump kit that I have not put on yet. Could that cause an issue like this ? At very low idle no water comes out but once I give it just a little throttle then water starts out the pee hole and all seems fine. Since I have no idea when it was replaced last I got a new water pump kit and plan on changing it soon.


Waterpump wont cause the issues about losing throttle, but it sure will cause an overheat. I would DEFINITELY change out the waterpump before your next outing. If you aren't peeing at idle that likely means the waterpump has lost its "spring" like rubber does after a number of years. Just prevent a future issue.
 

Tim Frank

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Tim: I do have a water pump kit that I have not put on yet. Could that cause an issue like this ? At very low idle no water comes out but once I give it just a little throttle then water starts out the pee hole and all seems fine. Since I have no idea when it was replaced last I got a new water pump kit and plan on changing it soon.

A compression test will tell you whether the head gasket is OK....which could have been caused by overheating.

Blown head gasket.

You have not mentioned what you did re: gas in the original tank.
It could be as simple as water and crud in the tank.

Follow the troubleshooting steps in the "Secret Files".
Verify compression/spark/fuel. Rectify each one in turn that is faulty.
 

kevinstan

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With a blown head gasket wouldn't it be spraying water everywhere while running ?
 

kevinstan

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I did empty the tank and hoses and filter and primer bulb and started again with clean gas and oil mix. I am also using the johnson evinrude fuel stabalizer while running.
 

Tim Frank

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With a blown head gasket wouldn't it be spraying water everywhere while running ?

Not necessarily. Could be blown between cylinder combustion chambers, or from combustion chamber into exhaust loop.
 

kevinstan

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I am going today to get a compression tester and check it out. What are good acceptable numbers for this motor ? And what kind of numbers should I be concerned about or will be the tale tale signs of a problem ?
 
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