Speedo Gauge Slow to respond (and tach off sometimes)

[Liamfm]

1997 Sport Nautique - Left speedo became very slow to respond after I tried to fine tune with the knob. Maybe unrelated, but seems to have happened at the same time. Tweaking the knob doesn't solve it. I can get it to show the right speed, it just takes a long time to get there, and a long time to fall back down. Pulled the dash, tried to blow (lungs) from the gauge back (with boat in the water). If any air was making it through, I couldn't really tell. Just got red in the face! Thoughts? Clogged line? how to unclog?

2nd issue - last year on vaca, tach started reading high by about 700 rpm at 36mph. Should read 3700 but was up around 4400. Took the dash off, turned the cylinder selector on the gauge, put it back and all was good for a while. Problem came back again recently. Any way to solve this "long term"? Take the gauge off and use contact cleaner somewhere?

Thanks in advance!

[beamons]

IMO, I think they are unrelated. If you have the speedos(airguides) that I think you do they have a cylinder in the back that relays the pressure from water to air. The best way to fix this is get an air compressor and turn it down to 30 psi and then blow through them a bit from aft to bow. This will free them up a little and help them work more smoothly.
Your tach is similar in that the age and slight lack of use cause them to not work as smooth. Keep working the knob on the back a bit more and possibly put some contact cleaner, or better yet, a suitable lubricant in the gauge.


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[Liamfm]

Thanks! I'll give the compressed air a try. It's hitting the trailer Saturday for vacation again. I did twist the knob a bunch this last time. Not sure how I'd get any contact cleaner in there though, without dismantling the gauge.