1981 Johnson 90 bogs down after 2500 RPM

adestin

Cadet
Joined
Sep 16, 2002
Messages
8
I recently purchased a 1981 Johnson 90 and it ran fine the first day I used it (typical!). It starts fine and idles fine but at 2500 RPM it tries to plane, then bogs down back to idle.<br />Any ideas??
 

rickdb1boat

Supreme Mariner
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Jan 23, 2002
Messages
11,195
Re: 1981 Johnson 90 bogs down after 2500 RPM

Make sure you have spark to all cylinders. Check fuel lines,bulb and Vent when this happens. Does the bulb stay firm? Just a start! Let us know more!
 

Brew

Petty Officer 2nd Class
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Jun 9, 2002
Messages
121
Re: 1981 Johnson 90 bogs down after 2500 RPM

I agree with Rick. First thing to check is that you have spark at all the plugs. Assuming you do, check the compression on all the cylinders (if you don't have a compression gauge, you can pick one up at any auto supply place for about $15.).<br /><br />If that all checks out, start looking for an air leak in your fuel system. If your primer bulb goes soft, this is a good indication that air is getting in somewhere. Follow the fuel line from the tank all the way to the fuel pump and make sure all connections are tight.<br /><br />If that all checks out, then you want to start looking at the carbs. You can get carb rebuild kits from any dealer for about $20 (I think) per carb. Really isn't much to the process other than replacing a few gaskets and a needle valve. While you have them apart, use some aerosol carb cleaner to make sure you get rid of any old gummed up gas that might be in some of the passages. I had a similar problem to yours that resulted from a clogged high speed jet in one of my carbs.<br /><br />Above all else, get a manual if you don't already have one. It gives you detailed instructions and diagrams which are worth there weight in gold.<br /><br />Good Luck!
 

adestin

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Sep 16, 2002
Messages
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Re: 1981 Johnson 90 bogs down after 2500 RPM

Thanks for the replies. I really appreciate it. The bulb does stay firm. If I'm not getting spark to all cylinders, what should be done? Also, where is the best place to find a manual on this engine?<br /><br />Cheers and thanks again
 

Brew

Petty Officer 2nd Class
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Jun 9, 2002
Messages
121
Re: 1981 Johnson 90 bogs down after 2500 RPM

Manuals you can get in a variety of places. You can get one online by using link called "Manuals" at top of iboat webpage. Otherwise, you can try a bookstore, Johnson/Evinrude dealer or some department stores (I got mine at Wal-mart).<br /><br />If your problem turns out to be no spark at the plugs, then it's likely an issue with your powerpack. Unfortunately, I don't have much experience with electrical problems, but I'm sure someone here can help out.<br /><br />Assuming your spark and compression tests rule out those areas as problems, I would really concentrate on your carbs. A clogged jet in a carb has led to many a sputtering engine.<br /><br />Good Luck, and keep us posted.
 

adestin

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Sep 16, 2002
Messages
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Re: 1981 Johnson 90 bogs down after 2500 RPM

Well, I've changed the fuel pump. The plugs were fouled (after 2 slow runs) so I changed those. I checked for spark to the plugs and one plug has no spark. What's the cause of this and how would I fix it? Also, any idea where the fuel filter would be for this engine?<br /><br />Again thanks for all your help!
 

ob

Admiral
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Aug 16, 2002
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6,992
Re: 1981 Johnson 90 bogs down after 2500 RPM

Check all ground lugs on engine for good contact.Could just be coil defective on cylinder in question.You can swap coil with other for check.If no change possibly powerpack.Generally an inline filter on inlet side of fuel pump under cowl.Look for White plastic unit.
 

adestin

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Sep 16, 2002
Messages
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Re: 1981 Johnson 90 bogs down after 2500 RPM

I will be checking the coil this afternoon. Again, I'm waiting on my manual. Is there 1 coil per plug and if so, what does it look like and where is it located.<br /><br />Lost without this manual!!<br /><br />Thanks!
 

ob

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Re: 1981 Johnson 90 bogs down after 2500 RPM

they'll be fastened to side of engine near plugs. trace plug wire to them and you'll see them.
 

adestin

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Sep 16, 2002
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Re: 1981 Johnson 90 bogs down after 2500 RPM

OB, can't thank you enough for your help. One more question..should the vent on the gas tank be open during running or closed?
 

ob

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Aug 16, 2002
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Re: 1981 Johnson 90 bogs down after 2500 RPM

Open,so fuel can flow freely to suction side of pump.If it's closed think of it like a straw full of fuid with finger over top.
 

adestin

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Sep 16, 2002
Messages
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Re: 1981 Johnson 90 bogs down after 2500 RPM

I traced down the powerpack...or is it the coil? Like you said, it's mounted near each plug but I don't know if it's the coil or powerpack. How can you tell the difference and which is which?<br /><br />Thanks
 

ob

Admiral
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Aug 16, 2002
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6,992
Re: 1981 Johnson 90 bogs down after 2500 RPM

The coil will have two plug-ins.One from powerpack and the other is your sparkplug cable.Will be one coil for each cylinder.I believe your motor has two power packs.One for each bank.
 
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