Speedometer Clogged

My speedometer is not working properly. It says I'm running 20-25 mph at full throttle (which is actually 60+). I've been told the speedometer wire is clogged. What is the procedure for clearing it? Difficulty level? Thanks

150 Mercury XR4

this has happen to me and what I did was un hooked the tube frome the speedometer and at the end connected to the lowere unit asuming this is where your pick up is. used compressed air this blew out a small peice of wood. If yours has the seperate intake mounted to your transom I would look there first for obstructions or breaks .

Longhorns1,
On the Mercury's there is a small pin hole on the back side of the lower unit. Take a small drill bit that will fit in that hole, and turn the bit with your fingers not with a drill. Most of the time there is bark that gets stuck in that hole, witch will stop the flow of water going in to read the speedometer. Very easy procedure, 99% of the time when it is doing what you are describing this will fix it.

If my memory serves me correctly, I believe a 5/32 drill bit fits perfectly. Like Ranger21 said, be sure to just turn it with your fingers and DO NOT ATTACH TO A DRILL!

If you dont have a drill bit use a small hook.

Don't know if I'd use compressed air or not. Might blow the tubing off the fitting inside the LU. Go the drill bit & finger route. Better to use one that a little small than just a fit. After you get the bulk of the trash out, then take your splice apart and flush with water to get the last out so it won't make it's way to your speedo.

I have a little drill bit set that came with
my cutting torch as a tip cleaner and it works
great. I'm glad I read this I had forgotton that
I stopped mine up Wednesday and I have to clean it out.-----gozzie