# 50hp Johnson sputters at high speeds



## JasonL (May 17, 2011)

I just recently purchased a 1984 50hp Johnson outboard that runs great until I get to 30mph then stutters until I bring the throttle back down to about its sweet spot of 25mph.

I recently had a mechanic look at the motor and he said it ran great and aced all of their tests, but once I get it out on the water this issue comes up.

The bulb on the fuel tank gets hard and the motor starts and idles fine once warmed up.

Any suggestions or assistance would be helpful.


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## Jason (Oct 2, 2007)

Check the connector from the gas line to the motor and the gas line to the gas tank. Those connectors do not last and will get loose causing air to get into the line. Mine did the same thing and a $6 new connector fixed the issue.


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## JasonL (May 17, 2011)

Jason said:


> Check the connector from the gas line to the motor and the gas line to the gas tank. Those connectors do not last and will get loose causing air to get into the line. Mine did the same thing and a $6 new connector fixed the issue.


Did your issue only happen with the higher speeds like mine or what is sputtering all the time?


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## GWally (May 16, 2009)

I have had 2 48 Specials which I think are basically the same motor. Replaced the first since I found a good deal on one that had tilt/trim installed when it was new. I have had this problem and others (it really hates to idle). I used to end up getting carbs cleaned every year or so til a Cajun mechanic told me a trick (?). Now, when it misbehaves, I pull the carb covers and spray Sierra Carbon Free in the throats, high speed jets and get some in the fuel bowls (I spray it in, put my finger over the hole then quickly put the drain screw back in so some stays in). I let this sit overnight and so far, my "stumbling" is gone the next day. Could the high speed jets be clogged? This has saved me a lot of trips to my mechanic and so far, over the past 4-5 years has kept me on the water.


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## JasonL (May 17, 2011)

GWally said:


> I have had 2 48 Specials which I think are basically the same motor. Replaced the first since I found a good deal on one that had tilt/trim installed when it was new. I have had this problem and others (it really hates to idle). I used to end up getting carbs cleaned every year or so til a Cajun mechanic told me a trick (?). Now, when it misbehaves, I pull the carb covers and spray Sierra Carbon Free in the throats, high speed jets and get some in the fuel bowls (I spray it in, put my finger over the hole then quickly put the drain screw back in so some stays in). I let this sit overnight and so far, my "stumbling" is gone the next day. Could the high speed jets be clogged? This has saved me a lot of trips to my mechanic and so far, over the past 4-5 years has kept me on the water.


Thanks for the information. I went to West Marin and picked up a can of this stuff. Is this pretty much the same?

http://www.westmarine.com/webapp/wc...eFLINr5t8Qg&ls_affid=m4e4PA*fW9Q#.UcytxZzvt3s


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## lastcast (Oct 12, 2007)

Almost sounds like your prop. How bad are the nicks and how true?


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## JasonL (May 17, 2011)

lastcast said:


> Almost sounds like your prop. How bad are the nicks and how true?


I was actually looking at the prop yesterday and thinking that it might need to be replaced. I'll get a pic of it when I get home today and upload it to this post and hopefully you can give me your opinions. 

Would a beat up or ground down prop cause this issue?


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## jcoss15 (Oct 11, 2010)

Your prop could be slipping at higher rpm's...


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## JasonL (May 17, 2011)

Here is what my prop looks like. Thoughts?


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## GWally (May 16, 2009)

JasonL said:


> Thanks for the information. I went to West Marin and picked up a can of this stuff. Is this pretty much the same?
> 
> http://www.westmarine.com/webapp/wc...eFLINr5t8Qg&ls_affid=m4e4PA*fW9Q#.UcytxZzvt3s


I don't know. I got it at NAPA (the get something for anything that runs store in Chauvin LA). When you go to full throttle does it run smooth up to that "stumbling" point? When I had a prop problem, the motor would run smoothly up to high rpms but the boat would sort of "stumble". It was the bushing.


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## JasonL (May 17, 2011)

GWally said:


> I don't know. I got it at NAPA (the get something for anything that runs store in Chauvin LA). When you go to full throttle does it run smooth up to that "stumbling" point? When I had a prop problem, the motor would run smoothly up to high rpms but the boat would sort of "stumble". It was the bushing.


Yep, it runs great until the last 25% of throttle, then it runs for a few second and then stutters, then runs good for a few more, then stutters until I throttle down.


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## jcoss15 (Oct 11, 2010)

The hub on the inside of your prop may be wore out...not sure just a thought.


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## pappastratos (Oct 9, 2007)

JasonL said:


> Yep, it runs great until the last 25% of throttle, then it runs for a few second and then stutters, then runs good for a few more, then stutters until I throttle down.


Sounds like a fuel flow or carb problem. Could be sucking air around a fuel line fitting like primer bulb, the fuel line disconnect at the motor. Or motor running out of gas, that would be a fuel line restriction, fuel pump getting weak. I had a truck do the same thing, it was the pump. Finally you could clean the carbs, disassemble & blow out the fuel passages


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