If you have an SX-550 that has been modified in any way - even just the rev limiter removed - anything at all changed - you will be wise to do the following modifications to insure reliability. And the cost is minimal.
First - remove the ride plate and the brass fitting that screws into the pump. This brass fitting is a 90 degree affair and it often has a poorly drilled interior. Use as large a drill bit as you feel safe using and drill out the brass fitting from both sides. It is not uncommon for some of these fittings to have been only partially drilled making the "turn around" center part real small - like maybe a 1/8 inch hole or less. Putting the fitting into a vise or even a pair of vise grips will allow this drilling safely - go slow and straight and make sure you go all the way to the end - stop point - it is best to use a drill press and to set the arrangement up to "stop" at the end of the fitting to get maximum distance into the fitting - without going through. Visual inspection is clear and easy. This may seem like a minor item - taking out a small amount of brass - but - remember we are working with pi here - so - a 1/2 inch hole will flow 3.1416 TIMES the water that a 1/4 inch hole will flow. By merely going slightly larger one can often double the water flow amount. Re-install the 90 degree fitting and pay close attention to the factory water line where the flex rubber hose attaches to it. Sometimes in assembly the water line will get smacked by the pump or pinched in some manner. It is simple to take a file handle end or any other similar - small to large - tool and open the line back up to full size.

Next remove the brass fitting from the exhaust manifold - matters not if it is stock or aftermarket. Drill it out using the same method. And re-install checking the water line that the hose attaches to the same as you did on the pump. This water line that goes through the hull is very soft and easily pinched - so - close inspection is advised.

Now - you have a good flow of water TO the motor.
As these are an alloy cylinder and head - heat dissipation is fast and excellent. The head gasket slows the flow of water to the very top of the motor and does a pretty good job of equalizing the flow of cold water around the cylinder. The head - however - is another "miss".
When the ski is traveling through the water the nose is elevated which will mean the motor is considerably higher at the front than at the rear. The factory outlet on the head is at the rear. This arrangement will allow an air bubble to form over the front cylinder. In a bone stock motor - it is not an issue - but - still not right. SO - Turn the head around. You can usually re-use the gasket if you’re clean and careful - remove the brass fitting and drill it out as you did the pump fitting. Re-install and set the fitting toward the starboard side. You will need a longer hose to re-connect your "out" line to the exhaust. This short piece of hose is all this mod will cost you. Most all of you will be best served by this modification and few will need to do what is described below.
Some aftermarket heads and exhaust systems require a different water system. If you want to - the other option to service this arrangement is to remove the head and drill and tap a new outlet in the front of the head. A 1/8th inch pipe thread tap is cheap and easy to use. Buy a new brass fitting - your choice of straight or 90 degree - but - do NOT drill either of the head fittings. Re-install the head - you now have a fitting at either end of the head. Run the rear exit line to the exhaust because that is going to be the most consistent flow of water and you do not want to overheat the exhaust. Run the front line to an outboard water outlet ( pisser) - the stock one (1/16th inch inside diameter) is too small - eliminate it and use a free flowing larger outlet. This can be a simple brass fitting as used on the head - straight with a nut on the outside of the hull. This simple one line to the exhaust and one to the "pisser" is usually a near perfect set up. Some exhausts will be better served to regulate downward the amount of water that enters the exhaust pipe and muffler - this will simply mean the "pisser" will flow more water if that restriction is used in the exhaust line. Be VERY careful to check and make sure the exhaust is not overheating. Simply running the boat on the water for a few minutes and checking the heat will give you the answers - the water box or muffler should never be too hot to touch - but - maximum horsepower will be attained by using as little water as possible in the exhaust system. Trial and error is the game here. But the final results are worth it. If you have an alloy water box and a half pipe you can restrict the water flow in the line from the header pipe to the stinger if you wish. It is quite remarkable how little water one can use and "get away with it" - but - be careful - experiment with different restrictions - and - opt on the side of more water - not less. You never know when a piece of leaf or a rock will clog or restrict a line.
Always remember - if the ski suddenly sounds louder - it probably has a plugged line - shut 'er off as quickly as you can - and find the problem.
THIS water line system is ONLY for alloy cylinders and heads - it is NOT for the iron cylinder motors made from 1981 thru 1990 - THAT water line system will be explained in another post.
 
Written by Cliff Jones / JetCo