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'93 Evinrude 90 Loses Power at WOT

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BillyGA

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[FONT=&quot]My VE90MLETS cranks and idles normally. However, when I take off and get on plane the engine loses power and seems to be "missing" after approximately 15 seconds. I back off of the throttle and come to an idle for 15 or so seconds then take off again. The engine seems to have full power but loses it after 15 or so seconds. I am again able to bring her to idle, take off, and then lose power. This process seems to be able to be repeated in the same manner as much as needed to get back to the boat dock. The oil tank has plenty of oil in it. I think the amount of "blue smoke" coming from the exhaust at idle is normal to indicate the engine is getting oil. Important to note: The tachometer indication has been intermittent for 10 years now. It might work fine for 10 minutes, stop working for five minutes, bounce around a minute or two, etc. A mechanic told me years ago some electrical part (don't remember what part) might be going bad and may eventually have to be replaced. Any ideas?[/FONT]
 
The tach jumping is probably either a bad connection, or your rectifier/regulator going out. Neither would cause the symptoms you describe.
From your description it sounds like all cylinders are not firing. Could be from lack of fuel or lack of spark.

First thing the experts are going to want to know is compression numbers from each cylinder, and will the spark on each cylinder jump a 7/16" gap.

You can try a drop test: While it is running, pull each plug wire one at a time and see if there is any change. If not, that cylinder isn't firing.
 
riopga said:
The tach jumping is probably either a bad connection, or your rectifier/regulator going out. Neither would cause the symptoms you describe.
From your description it sounds like all cylinders are not firing. Could be from lack of fuel or lack of spark.

First thing the experts are going to want to know is compression numbers from each cylinder, and will the spark on each cylinder jump a 7/16" gap.

You can try a drop test: While it is running, pull each plug wire one at a time and see if there is any change. If not, that cylinder isn't firing.
Click to expand...

Thanks for the quick reply. Your analysis, lack of fuel or lack of spark, is hopefully spot on. For starters I'm going to change the fuel filter at the suggestion of my neighbor who works on small engines. I've had a clogged fuel filter on an automobile before and this acts just like my auto did many years ago. When not under a heavy load it runs fine. Shortly after loading the engine it starts stalling, probably from lack of an adequate amount of fuel. When I back off it is running fine again. Under heavy load it starts stalling. Hopefully a new fuel filter will solve my problem. If not, I will start troubleshooting the spark using your drop test method for starters.

Thanks again.
 
I apologize, my description of the issue was misleading. I don't think the engine is "missing" when it loses power. It acts more like a lack of fuel. My neighbor, who works on small engines suggested a clogged fuel filter. Yesterday, I was able to speak to a friend who is a semi-retired marine mechanic. Right off the bat he suggested the check valve where the fuel line connects to the fuel tank is probably stuck, causing fuel starvation when the engine is under load. He recommended removing the ball and spring (check valve) as it isn't needed on my boat due to the fuel tank is lower than the engine. He also suggested I could "blow out" the fuel filter rather than replace it. I did that and will see if that changes anything. If not, I will have to tackle the check valve which is a PITA to get to and the reason I'm trying the easier thing first. I'm also going to add a little oil to my gas in a 100:1 ratio and give the check valve a tap or two to try to free it up, assuming its stuck. I'm assuming the oil added to the fuel in the tank might help lube the check valve and prevent future problems. Any ideas on that theory?
 
Yeah, you can't tell by listening. They can sound fine on 3 cylinders. If your ignition checks out (good compression, spark jumps 7/16th inch gap), then I would look at the high speed jets way in the bottom of your carbs.
 
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BillyGA said:
I apologize, my description of the issue was misleading. I don't think the engine is "missing" when it loses power. It acts more like a lack of fuel. My neighbor, who works on small engines suggested a clogged fuel filter. Yesterday, I was able to speak to a friend who is a semi-retired marine mechanic. Right off the bat he suggested the check valve where the fuel line connects to the fuel tank is probably stuck, causing fuel starvation when the engine is under load. He recommended removing the ball and spring (check valve) as it isn't needed on my boat due to the fuel tank is lower than the engine. He also suggested I could "blow out" the fuel filter rather than replace it. I did that and will see if that changes anything. If not, I will have to tackle the check valve which is a PITA to get to and the reason I'm trying the easier thing first. I'm also going to add a little oil to my gas in a 100:1 ratio and give the check valve a tap or two to try to free it up, assuming its stuck. I'm assuming the oil added to the fuel in the tank might help lube the check valve and prevent future problems. Any ideas on that theory?
Click to expand...

With regard to the check-valve (anti-syphon valve) mentioned by the mechanic, I got the fitting on top of the fuel tank where I can get to it now and discovered it has an inline valve (picture attached). Does anybody know if it would have a check-valve in addition to the inline valve? Is this area worth checking out or am I barking up the wrong tree? I still need to check the ignition as recommended but haven't gotten that far yet.
 
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