mercury 40HP- Throttle not opening fully

Hi, Great to find this site and hope you guys can help! I bought a 1973 Glastron boat with a 1974 40 Hp mercury engine "402" and I looked into the carb and the throttle plate only opens about 1/4 of the way? Is this an easy repair as this is my first boat/ motor and know very little about how things work. I would like to find someone in CNY that could help me or repair this at a resonable cost, Thanks Don. enduro97@msn.com

Re: mercury 40HP- Throttle not opening fully

I have the same motor with the exception that mine is a 1979, but they are still extremely similar. I have been rebuilding mine since February of this year, so I have learned a ton about this motor. Let me begin by asking you, when you say the throttle plate only opens 1/4 of the way, do you mean that is all that it opens at WOT (wide open throttle) which is when the gear selector is in forward and pushed all the way down until it cannot travel any further?

Re: mercury 40HP- Throttle not opening fully

Yes, The throttle is only opening 1/4 of the way with the control lever pushed forward all the way. Any help would be appreciated, Thanks, Don.

Re: mercury 40HP- Throttle not opening fully

That is definitely an issue. The throttle cable can be adjusted using the barrel retainers on the cables where they connect to the motor. there is a locking lever that holds both of the barrels on the right side of the motor (if you are standing in the boat looking at the motor). Undo the clip on the barrel retainers and you can access them. I am not sure which cable is the throttle, as I have not tweaked mine in awhile. I think it is the bottom one. You can twist the barrel retainer on the threaded portion of the cable. Like I said, I haven't tweaked mine in awhile so I can't recall what direction will open the throttle more but you can try both directions and see which does it more. There is also an Idle stop screw above the barrel retainers that you can adjust to allow the throttle to close fully when it is in neutral, which would be the correct idle position. If any of this does not make sense, let me know and I will email you some pictures of my motor and what I am talking about.

Re: mercury 40HP- Throttle not opening fully

There is a friend at work that says there are a few adjustments that need to be done in a certain order so everything works the way it should. I see the cable adjustment your talking about and that looks easy but want to be sure before I begin moving things. Thanks, Don.

Re: mercury 40HP- Throttle not opening fully

Hey Guys, I went out today and found a turn buckel that I turned so the throttle now opens fully. Is this adjustment OK or did I mess it up? I have not got it in the water yet to see if it works?!?!? Is there anyone in central NY near Fulton that could look this over for me? Thanks, Don. enduro97@msn.com