[Swekro]

Hi! Happy to find your forum and all knowledge here!

Just bought a 2005 Mariah sx18 with merc 4,3 , lowely boat but had a few fixes
The rpm and speedo gauge wont work, the other (fuel, oil preassure, charging and temperature works fine.

I tryed to find the cable from the rpm gauge to coil but couldnt locate it.
The gauge dont move at all when ignition is on(should it?) have turn the selector of cylinders on backside of the gauge with no luck.

Allso think the prop is to small( it has a 14x19 now in like new condition), it get out of the water very fast and pull strong but seems to over rev at higher speeds, as the gauge dont work i dont know how much it revs, the speedo on my iphone showed 35mph then i didnt push it harder.

What about a 4 blade prop?

Thanks from sweden!

[Motoxxx43]

Nice looking boat! A 4 blade in the same pitch will drop your rpm roughly 100-200 rpm. I don't recall what the 4.3 has for WOT range but that would be a good place to start. See where you are running currently an go from there.

[mikeyt]

I saw this same post on the Facebook Mariah Owners group. I'll repost my answers;

Speedo: It's likely that the pickup hole on the front of the outdrive is clogged with debris / corrosion. Easiest way to clean it out is to remove the tubing from the backside of the speedo itself and use a compressor to blow air back thru the line. That air should blow out any blockage.

Tach: Likely issue is poor wiring connection.

Prop: Boat likely came with a 14" x 19" 3 blade aluminum prop. You need to get the tach working first and then sort out what prop change (if any) is needed. The WOT range for the 4.3 is 4400 - 4800 rpms. Going to a 4 blade with the same pitch will actually raise your RPM's by about 150 - 200. I run a 14.25 x 20" - 4 blade SS Apollo prop on my 180 and my WOT rpms are sitting at 4850.

Good time to read this: Basic Propellor Rules