7.5 john power loss when hood is on

W

wet rat

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Jul 26, 2011
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I just purchased a 1981 johnson 7.5hp. When i took it out for the first time it had very little power and while running full speed I took the cover off and my power almost doubled(still not enough power to plane off). the air vents by the handle on the hood are clear. I just wanted someone to steer me in the right direction any help would be greatly appreciated .
 
R

Rick.

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Jul 30, 2006
Messages
3,740
Re: 7.5 john power loss when hood is on

9.5's are well know for exhaust leaks into the cowl which starves the carb. of air. Sounds like you may have the same situation. Have you noticed and exhaust smoke under the cowl? The only other thing that comes to mind is there anyway the cowl, when sucked down by the latch, could be pinching your fuel line? Best of luck. Rick.
 
W

wet rat

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Re: 7.5 john power loss when hood is on

there was some smoke so i believe you are dead on thanks. is this something a amature could fix or should i leave it to an pro.
 
R

Rick.

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Re: 7.5 john power loss when hood is on

OK now I need to confess. I am not familiar with the 7.5 at all so hopefully others will chime in here and tell you where exhaust might get in under the cowl. You can look also and see if there is anything obvious. Your probably going to need a OMC service manual at some point. http://epc.brp.com/SiteMods/BRP_Public/BRP_Public_Login.aspx?ReturnUrl=/Index.aspx Follow this link for a parts bread down of your specific engine. Rick.
 
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fmalott

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Jun 28, 2010
Messages
561
Re: 7.5 john power loss when hood is on

i was fixing a 75hp motor the coil was bad when i was replacing i thought i would clean the carb the carb was full of this beige type of dust so i cleaned very well put everything back together new coil was working good but ran like crap so i took the cover off and the carb was all clogged up again with this beige dust what it was the cover had this insulation foam on the side of the cover it was so old it was turning to dust so everytime i put the cover on turn on motor it would suck all the old foam dust in the carb keep that in mind when looking at the problem
 
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