On a early eighties model 15hp suzuki 2 stroke how do you know if the water pump is working?

Lean fuel mixture

you have to disconnect the shift rod first

first bit of advice
do not use e-mix fuels in outboard engines
WHY
because ethanol separates from the fuel if not used continuously so letting it stand between outings is not good
secondly ethanol is hygroscopic which means that it absorbs moisture from the air that is going in via the tank vent and that results in corroded aluminium parts and rusted fuel tanks and outboards operate in a very moisture laden environment
now for the problem
being a late model engine , it should be a 4 stroke and like any 4 stroke engine , check the timing belt/chain, crank/cam position sensors , ignition module
it is important to check all harness connections as salt water rapidly causes corrosion in electrical connections and components
have the service agent do a scan for fault codes remember this
Suzuki out board 2 stroke motors were used in the early suzuki 4x4 cars and modern 4 stroke engines are simply car engines on end

If your old engine/control has the same 'options' as the30hp, yes everything is compatible... (Electric start or trim )
The throttle and shift cables are allways compatible...

5.00 USD
Suzuki Rm125 Service Manual Repair 2004 Rm 125

Instant download of the official manual for the RM125 2 stroke bike. Specifically for the 2004 model, but can also...http://www.tradebit.com/filedetail.php/9003904-suzuki-rm125-service-manual-repair-2004-rm

I hope that this helps you and please do not forget to rate/vote and place a testimonial on my advice.

Wicked Angel

get a repair manual from Fixya

I have a 1979 Johnson 15hp Long shaft, and as a single motor just followed the rule of a shortshaft motor for a short transom and a longshaft for a deep transom. You have a little adjustment in the mount clamp. You want enough shaft not to cavitate and want the trim fin below the hull. If this is a kicker motor you want it deep enough for water pickup but less deep for drag on fixed mount.