Back when I was in the boat business, the boats used in waterski
competition had compressed air that could be shot backwards through the
speedo tube to clear out whatever blockage there was.

For your problem, probably removing the tube at the speedo and blowing
(or shooting some compressed air) into the tube towards the pickup
(reversing the flow) should do the job.

*************************************************
Scott H. Sexton help@
www.sexton.com sexton.com
Eeyore's Birthday Party http://eeyores.sexton.com
*************************************************