1975 mercury 7.5 hp won't plane 10ft fyran?

Rotamax

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Joined
Feb 27, 2012
Messages
2
Hey my 7.5hp mercury thunderbolt had been sitting for a good 20 years in a barn, I replaced spark plugs,impeller and switchbox with a second hand unit, cleaned carb and replaced tote tank. It starts first pull and runs mint but in foward gear in the water it seems to only get 50% rpm. I have a 10ft fyran tinny. My mate has a 6 hp and he's going twice as fast:mad: any ideas? Thanks
 

jerryjerry05

Supreme Mariner
Joined
May 7, 2008
Messages
17,923
Re: 1975 mercury 7.5 hp won't plane 10ft fyran?

You sure you have spark on both cylinders?
Remote tank?Vent open?
Check the fuel pump.20 years old?? Needs to be rebuilt/replaced.
Compression test.These motors will run great on just one cylinder.
My neighbor has a 9.9 and ran it for a year with one plug wire off.
 

Rotamax

Recruit
Joined
Feb 27, 2012
Messages
2
Re: 1975 mercury 7.5 hp won't plane 10ft fyran?

Yea she's only running on 1, getting spark from both leads tho, could this be the switchbox? I will check compression 2morro when I get a tester. Thanks
 
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