Won't rev over 5000 RPM

KennyKenCan

Commander
Joined
Aug 26, 2002
Messages
2,501
I have a 1994 Mercury 135 HP V6, that will not go above 5000 RPM. :eek: <br /><br />I normally run a 14.25" X 21" prop. that usually topped out at 5300 RPM, so I changed prop to 14.5" X 17", which usually revs at 5800 RPM, but I could not get motor to turn more than 5000 RPM with the 17" prop! :mad: <br /><br />This is not normal! :confused: <br /><br />Any ideas??? :cool:
 

KCLOST

Commander
Joined
Jun 22, 2002
Messages
2,095
Re: Won't rev over 5000 RPM

With the 21P prop it "currently" runs at 5300rpm, or used to?<br /><br />Something doesn't sound right...
 

rickdb1boat

Supreme Mariner
Joined
Jan 23, 2002
Messages
11,195
Re: Won't rev over 5000 RPM

Got good fire on all cylinders? Good plugs? I know this is kinda out there, but are you sure it's a 17" pitch prop and have you tried running it again with the old prop to verify it's still running up to par?<br /><br />EDIT: I see you have gotton 5800 out of the new prop, so it must be a 17" pitch. Check the spark and plugs..
 

KennyKenCan

Commander
Joined
Aug 26, 2002
Messages
2,501
Re: Won't rev over 5000 RPM

This motor has always been run with the 21P prop for normal cruising, and it was consistanly running at 5300 RPM, 43.6 MPH, with that prop.<br /><br />I use the 17P prop for watersports, and that prop always turned 5800 RPM.<br /><br />Now with the 17P prop, the maximum RPM is 4900 - 5000 RPM.<br /><br />I checked the spark last season, using a spark gap testor, and all seemed fine.<br /><br />This problem began at the end of last season, and I wish to get it repaired before the beginning of this years season.<br /><br />Also top end MPH have dropped off.<br /><br />Use to be 43.6 MPH, according to the GPS, and now I can barely get over 38 MPH.<br /><br />Could the coils be becoming weak??<br /><br />Or could it more likely be a stator or switch box problem??
 

rodbolt

Supreme Mariner
Joined
Sep 1, 2003
Messages
20,066
Re: Won't rev over 5000 RPM

well if all the cylinders spark and compression is good then open up the fuel pump and rebuild it. buy a gasket set and do the carbs. its a 3 hour operation on a saturday afternoon and then you will know if its fuel or ign.<br /> good luck and keep posting
 
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