High Speed Problem. Not sure of cause

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basbalj288

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I have a 1976 Johnson 85hp outboard and it is having issues getting to top speed at WOT. It should be going 40 which was normal but lately it will randomly drop to 26 mph and then after more riding around drop to 10 mph and not sure the cause. It's highly frustrating. The motor runs smooth and doesnt sound like it's misfiring just not firing enough when it starts acting funny.

Background info...I've replaced the stator, rectifier, powerpack and water pump all last month and the first 2 trips out ran flawless and then the problem of losing RPMs at WOT happened again. What could be the problem....the timing, powerpack failure again, ignition coils bad...

Thanks for any help because I'm going to the lake saturday and would love to be closer to figuring this out
 
oldcatamount

oldcatamount

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Re: High Speed Problem. Not sure of cause

Ignition coils will do what you are describing. When a coil gets weak, it'll drop voltage as it heats up causing lack of rpm. If you have a multi meter, you can test them but I'm not sure of the test numbers. There is a great website (www.cdielectronics.com) with the testing values you'll need.
 
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basbalj288

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Re: High Speed Problem. Not sure of cause

The fuel system is fine new hoses and filter. Also when I'm at WOT I had a friend prime the bulb to see if it wasn't getting enough gas and that didn't cause it to do anything different.
I have been told before it sounds like weak ignition coils but then I've been told that coils aren't usually a common cause of any problem so I didn't buy new ones because I wasn't sure. I will test it based on the numbers it gives me in my manual. Are there any other symptoms of weak coils? Thanks
 
oldcatamount

oldcatamount

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Re: High Speed Problem. Not sure of cause

Weak coils are tough to diagnose. A timing light would show you if there is a cylinder that's not firing right and that would lead you to the bad coil.
 
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Monte1961

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Re: High Speed Problem. Not sure of cause

Is there a chance it might be overheating?
 
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Daviet

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Re: High Speed Problem. Not sure of cause

It sounds like you could have some high speed jets plugged. Have the carbs ever been overhauled?
 
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basbalj288

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Re: High Speed Problem. Not sure of cause

-I thought about it overheating so I replaced the water pump impeller and now it is pumping water much better but didn't fix the high speed problem.
-I have a timing light but all I've used it for is to check the timing advance to set it to the correct degree...how would I determine if there's a bad coil with it? I'm interested to hear because I will try that tomorrow.
-The carbs were supposedly (SUPPOSEDLY) rebuilt by a mechanic a few months ago but I have no idea if they were really or not...I took the boat out of there before he finished the 2 things I had asked him to because the boat had sat there for 6 weeks so I don't know for sure but "supposedly" so...any way I could check to be sure?
 
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Monte1961

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Re: High Speed Problem. Not sure of cause

When the engine starts acting up, put the timing light on each of the wires and check for a good strobe. If intermentint or unsteady flash will tell you something electrical is wrong.
 
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basbalj288

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Re: High Speed Problem. Not sure of cause

Well that's easy enough. I will do that Friday morning when I go to the lake again and let you all know the results.
-The weird thing to me is that the boat cranks normal and gets to speed pretty normal but then once that second throttle arm starts to move it's a guessing game of whether it will catch and pick up speed like it's supposed to or whether it just seems like its running at half power (or less). This doesn't sound like a powerpack issue to anyone? (remember I just replaced it a month ago)
 
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AlTn

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Re: High Speed Problem. Not sure of cause

take a spray bottle with fuel mix in it along when you test with the timing light...if the ignition seems normal, spray the fuel mix into each carb throat to determine if the motor bogs or picks up..this can help diagnose fuel issues
 
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Monte1961

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Re: High Speed Problem. Not sure of cause

Try the suggested items first, then let us know. At that point we can assist you in what way you need to go. Post back and let us know.
 
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basbalj288

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Re: High Speed Problem. Not sure of cause

Ok I will do those things...I got some homework over the weekend but I will be glad to try those things and let you all know the results.
Thanks so much guys!
 
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basbalj288

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Re: High Speed Problem. Not sure of cause

Thank you all for your suggestions but a special thanks to Daviet and AITn you all were correct! Yall win! The timing light seemed normal and I did a spark test and all the coils passed so I then went ahead and looked in the carbs (which were supposedly rebuilt by the mecanic in March). What I noticed when I took the panel off and we started going down the lake was that there was no gas being sprayed into the throat leading to the 4th cylinder (which would explain the one fouled, black, and glossy 4th cylinder plug with the other 3 being a normal grayish color). So I knew exactly which throat to spray gas in and when I did so the boat picked up to the normal speed if I kept spraying very fast. So I guess I will be either running cleaner through it and hope that it cleans itself out or rebuilding the carbs...If I take the carbs off to clean the high speed jet will I have to replace all of the beirings and rubber pieces and floats or can I just take the jet out and clean it?? (I've never done it before!)
Really thanks guys so much! I have been looking for the cause of this problem all summer and now I will be able to have many successful trips throughout the rest of the summer!
 
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Monte1961

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Re: High Speed Problem. Not sure of cause

Post back after repairs are made, and let us know how it turned out! Good Luck.
 
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basbalj288

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Re: High Speed Problem. Not sure of cause

Can I remove that drain plug without having to take the carb off of the motor? I saw the picture on that link and I can't find where to remove the screw that is shown to be right in front of the high speed jet..
 
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AlTn

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Re: High Speed Problem. Not sure of cause

can you feel it with your finger or see it with an inspection mirror?...low on the side of the carb bowl?
 
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Daviet

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Re: High Speed Problem. Not sure of cause

Should be one on each side of the float chamber, should be able to see them clearly.
 
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basbalj288

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Re: High Speed Problem. Not sure of cause

Yes I can see with the panel off and feel with the panel off where the gas is shooting out from. I guess now I'm asking if there's an easy way to access the jet with a thin wire without having to pull the carb off of the motor? That would be ideal!
 
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