Speedomoter not reading correctly????

[plane69]

Does anyone have any suggestions for checking the speedomoter intake on an Alpha1 drive? Will read @15mph when going over 40. Have taken an airgun to the intake, guage runns up tp 50mph. Back to 15 when in the water. Any ideas???

 

[hondon]

Re: Speedomoter not reading correctly????

Get your hands on a guaged pressure tester. Mighty vac comes to mind. Adapt it to fit into the speedo tube that comes out of your lower gearcase and pump it up to 5 psi.Should read 20 mph and hold that pressure without leaking off.If it leaks off you have a hole in the hose or the speedo diaphram.If all looks good there then the pickup is at fault.