MF 755 Yamaha 150

[mf755wahoo]

Got the chance to go out on our MF 755 for a couple of hours today - some respite from seemingly never ending rain and pretty windy weather for the last 3 weeks here in SW UK. We were on our way back, opened her up to 19knots, all fine, revs 4800 or so. Then I noticed that the Yamaha speed/knots display was playing up and was only showing a speed of 4 knots. No other malfunction signs, no change in engine sound, boat still planing nicely - GPS data showed SOG as 19knots.
When we came back off plane and then pootled into our berth the speed display did not sort itself out.
Presumably there could be a bit of 'crud' in whatever device is on the outboard that deals with speed through the water measurements. Any advice please?
Thanks in advance

[odetta]

Simple fix: use a small diameter drill bit to remove the "crud" from the opening at the front of the motor's lower unit. Unfortunately, this is easiest done with the boat out of the water or when swimming in the water and difficult to reach from the back of the boat. Might not be worth doing until you pull the boat, as you can rely on GPS speed readings....

[mf755wahoo]

Many thanks - will sort when the boat is out in Feb