Motor looses power at full throttle but picks up rpm’s when I decrease throttle

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Ga Aquadog

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Does it run smoothly when the RPMs decrease?
or
Does it sound rough and did the RPMS drop quickly?
I see a low speed idle screw on the starboard side of the carburetor but no high speed idle screw?
 

cyclops2

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No high speed adjustment screw is normal on those years of smaller Johnson & Evinrude.
 

thill

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Take the air box off (if it has one) and look down the carb and watch the butterfly while throttling up with the engine OFF, not running. At full throttle, the butterfly should be perfectly horizontal for maximum airflow. If your throttle cable is out of adjustment, it will open fully, and then continue past horizontal and close partly in the other direction. This will cause the motor to slow down. So you may actually be at full throttle when the handle is only turned 3/4 or so. I had this issue in the 25 Evinrude in my sig pic years ago, and someone here helped me.

You may need to do a "sync and link" according to the service manual to get everything working properly.
 

cyclops2

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I had a car with that same problem. Same cure of linkage adjustment.
 

Pappy

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Usually the roll pin in the throttle shaft will keep it from going too far past parallel. One side of the roll pin will land against a cast in boss on the outside of the carb. A small amount of over travel will not make a difference.
However if all else fails I would suggest purchasing a replacement high speed jet as the existing one may be worn. The ammonia content in a lot of 2-stroke oils wreaks havoc on the brass the jet is made of.
 

Ronbedard57

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Hi,
Ditto on the main jet. I'd take the whole carb to someone that could put it through a session in an ultrasonic cleaner.
Also ditto on the water pump! Not sure about your motor, but I'd definitely replace the shift rod seal, possibly the prop shaft seal(s), refill the lower case, pressure test. 32 years! Great find!
 

Ga Aquadog

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Take the air box off (if it has one) and look down the carb and watch the butterfly while throttling up with the engine OFF, not running. At full throttle, the butterfly should be perfectly horizontal for maximum airflow. If your throttle cable is out of adjustment, it will open fully, and then continue past horizontal and close partly in the other direction. This will cause the motor to slow down. So you may actually be at full throttle when the handle is only turned 3/4 or so. I had this issue in the 25 Evinrude in my sig pic years ago, and someone here helped me.

You may need to do a "sync and link" according to the service manual to get everything working properly.
 

Ga Aquadog

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Thanks. That makes sense. Can’t wait to check it. I will let you know what I find. I have been getting info. to check the high speed jet. This model only has a low speed jet.
 

cyclops2

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All carbs must have a high speed jet. Even if there is no adjustment screw for it.

Read post # 23 again.
 

Pappy

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Lordy.......
NO....you do not have a low speed jet. You have a low speed adjustment. Even you have noted that in an earlier post by you.
Are you going to get in to this mechanically and get something done or are we just getting writer's cramp here?
You still have not even agreed that you have to remove the starter to remove the carb.

Cyclops.....many engines of that horsepower DID have a high speed adjustment which was phased out by arouund 1965 or so.
 

cyclops2

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65 to 90 is a long time. My 1999 9.9 has a slightly rich jet. But a little rich is far better.
 

Ga Aquadog

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All carbs must have a high speed jet. Even if there is no adjustment screw for it.

Read post # 23 again.
Yeah I misstated it No adjustment screw is what I meant to say. I have the service manual. Doesn’t show one.
 

Ga Aquadog

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Lordy.......
NO....you do not have a low speed jet. You have a low speed adjustment. Even you have noted that in an earlier post by you.
Are you going to get in to this mechanically and get something done or are we just getting writer's cramp here?
You still have not even agreed that you have to remove the starter to remove the carb.

Cyclops.....many engines of that horsepower DID have a high speed adjustment which was phased out by arouund 1965 or so.
Take the air box off (if it has one) and look down the carb and watch the butterfly while throttling up with the engine OFF, not running. At full throttle, the butterfly should be perfectly horizontal for maximum airflow. If your throttle cable is out of adjustment, it will open fully, and then continue past horizontal and close partly in the other direction. This will cause the motor to slow down. So you may actually be at full throttle when the handle is only turned 3/4 or so. I had this issue in the 25 Evinrude in my sig pic years ago, and someone here helped me.

You may need to do a "sync and link" according to the service manual to get everything working properly.
Thanks that fixed my problem. 😊
 

thill

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Usually the roll pin in the throttle shaft will keep it from going too far past parallel. One side of the roll pin will land against a cast in boss on the outside of the carb. A small amount of over travel will not make a difference.
However if all else fails I would suggest purchasing a replacement high speed jet as the existing one may be worn. The ammonia content in a lot of 2-stroke oils wreaks havoc on the brass the jet is made of.
That depends on which motor it is and if it's adjusted properly. Mine was a late 90's Evinrude 25.

If it goes past horizontal, it can make a VERY noticeable difference because the edge of the throttle plate "scoops" air and disrupts the venturi that pulls the fuel. Depending on the carb design, of course.

Not trying to be snarky or combative, but it is definitely a thing.

Someone on this forum told me the same thing many years ago, and it solved my problem. I can't remember, but I think there was a max throttle screw that was missing or adjusted wrong. That, or the roller was adjusted by the PO so the plate never closed fully because it needed a carb cleaning. Either way, it was an easy fix. It didn't gain me any more speed, but I didn't have to feather the throttle to get WOT, just crank the handle and go.
 

Ga Aquadog

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That depends on which motor it is and if it's adjusted properly. Mine was a late 90's Evinrude 25.

If it goes past horizontal, it can make a VERY noticeable difference because the edge of the throttle plate "scoops" air and disrupts the venturi that pulls the fuel. Depending on the carb design, of course.

Not trying to be snarky or combative, but it is definitely a thing.

Someone on this forum told me the same thing many years ago, and it solved my problem. I can't remember, but I think there was a max throttle screw that was missing or adjusted wrong. That, or the roller was adjusted by the PO so the plate never closed fully because it needed a carb cleaning. Either way, it was an easy fix. It didn't gain me any more speed, but I didn't have to feather the throttle to get WOT, just crank the handle and go.
I truly appreciate everyone’s input. Thanks for taking the time to help. The problem was the throttle linkage adjustment.
 

thill

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For what it's worth, your very first reply was from Pappy recommending a sync and link. He nailed it on his very first guess. He only got more complicated as time went on, as it appeared that it was more than that, based on your replies.

I just happened to recommend the same thing much later.
 

cyclops2

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All those ADJUSTABLE screws Are the first things played with. Then you have a motor that is difficult to correct. NOTHING helps if using a guessing way to correct anything.
 
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