1990 Johnson 25hp surging

J

jackinabox

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Jul 17, 2007
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3
Hello All,
My first post here... I'm trying to help my elderly neighbor with her boat.
Unfortunately never worked on a Johnson before.

The engine will start and idle fine. If throttle is increased past 1500 rpm (a guess - no tach) the engine will increase speed then cutout then increase speed and cutout repeatedly. It will do this in gear or in nuetral.

It's difficult to describe in words. It sounds like the rpm limiter in newer cars when you push the pedal to the floor in Park.

Any Ideas??
 
tashasdaddy

tashasdaddy

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51,019
Re: 1990 Johnson 25hp surging

my first impression is it is flooding itself out. second is fuel delivery problem. both being carb problems. 1 st being the float is sticking and not closing all the way, the second being the high speed jet is partially clogged. it is in deep down inside the front drain plug, and requires a special screwdriver to take it out. 3rd is the the fuel pump is failing. 4 th link n sinc.

http://i155.photobucket.com/albums/s311/frankr_photos/FixedJetScrewdriver2.jpg?t=1177353186
 
J

jackinabox

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Jul 17, 2007
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Re: 1990 Johnson 25hp surging

Thanks for the reply - sorry about the double post, not sure how that happened.

I forgot to mention I did pull out the high speed jet and cleaned it. (they should put an access hole in the motor housing to get at that jet w/o having to remove the carb) Also pumping the primer bulb does nothing, nor does engaging the electric primer. I also pulled the hose from the primer to make sure it's not dumping fuel.

I did not check the float needle and seat. I'll pull the carb back off and check that out.
 
reload

reload

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Jun 29, 2004
Messages
368
Re: 1990 Johnson 25hp surging

Sounds more like it is starving not flooding. As stated it could be fuel pump or dirt in carb. Pull pump and clean first (easiest).
 
M

mikesea

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Re: 1990 Johnson 25hp surging

the carb has some small passages that can get gunked up that wont get cleand without disassembly
 
J

jackinabox

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Jul 17, 2007
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Re: 1990 Johnson 25hp surging

Thanks for the input everyone!
I rebuilt both the fuel pump and carb. I've rebuilt many carbs and never saw one as clean as this one, hardly a speck of dirt even on the outside of the carb. I blew every orifice out with compressed air. I checked the fuel pump flow and it's very good. But....

The surging is still there exactly as before.

I'm starting to think ignition problems.... Have not even looked at the plugs because it runs so good up to about 1500 rpm's with no engine misfire at all.
It's not getting hot mostly because I never run it more than a minute, but also has a good stream coming out the pee hole.

Any other ideas would sure be welcome...
 
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