Is Fuel delivery Routeing ?
The carburetor fuel pump draws the fuel into it from the delivery circulatory, then pushes it thru the carbs, into the return to the circulatory chamber line. If you remove the return line from the carb exit nipple, fuel should come out when you spin the engine. Thrus, It is Not routeing. A clog is restricting fuel flow. Either it cannot draw fuel or it cannot push fuel.
Do the purge/leak test for fuel routing, and Test or replace the rectifier in the electrical box.
Once you first notice that the motor is not performing as it should, immediatly park it and find out what is wrong. Do not keep trying to ride it. That is how motors get destroyed for no good reason other than it needed fixing before the damage is done. Now you need to do a compression test to see if you damaged your pistons/rings & cylinder walls. Hopefully, the rectifier has gone south and that is why it will not rev out properly, a very common cure for this type problem.
there is more often than not a problem inside a carbureator, typically, those problems are water sitting in the carbs rusting up stuff, needle and seat valves that are stuck shut, diaphrams that are stiff old and hard, sometimes vulcanized ( glued ) to the diaphram cover plates so they can barely move inward to open the needle valves when necessary, or just partially open the needle valve which reduces fuel flow, gasoline/oil varnished internal carb parts, clogged internal filters, bad fuel pump diaphrams, ect.ect.ect.
Then to add to the list, water in the bottom of the gas tank, or a gooey mess of hardened pre-mix oil thart seperated from the gasoline, a clogged up fuel selector valve, rotten fuel lines and last but not least, the wrong style inline fuel filter. The one small fuel pump that feeds two thirsty 720 carbs cannot put up with any restrictions caused by the wrong style inline fuel filter.
Also, knowing your carbs and fuel system is clean and flowing easily & properly is very important on old motors. A clean fuel system and carbs will go along way to keep you from needing a new motor premateurly.
Inspect the fuel separator/filter O-ring and gas tank vent one-way check valve. Remove the gas tank fuel bafel and clean the bottom screen, this is the most overlooked filter in the fuel delivery system. When clogged can overwork the drawing power of the carburetor fuel pump. Any Goo from deteriorated lines is immediatly recirculated into the outgoing fuel supply line. Any tubulented goo drops to bottom of the bafel when ski sits.
Disconnect the red wire to the rectifier and see if it run great. restart the ski several times to confirm and if everything worked, Rec is bad, This is the Rectifier test.
Open gas cap in case any pressure is in there, then re-tighten. Remove the gas supply line from carb
and put the hose end into a catch bottle. Remove the fuel return gas line from carb nipple and blow a small amount of air chuck pressure into return line. Watch routing fuel flow from
supply in a bottle, IF it routes good, the carb is faulty from a clog or pump diaphram has a hole.
Check pulse tube for clog, it operates the fuel pump with a push-pull or suck-blow as pistons
go up-down in engine case, that is how the mag carb pump actuates route pressure thru the carb, and back into gas tank . A WD-40 straw works good for that. Attach a 2'short fuel line to the tube and if you can blow into the crank-case, its clear of debris.
On dual carb systems, when the mag carb (it gets fuel first) clogs and the PTO carb starves as a result, and that cylinder runs lean, then seizes first. Running lean can cause Glow-plugging and the engine will Rev run-away. Pulling off the lanyard will not help. Asphyxiating by pulling choke and opening throttle may stop engine run-away. Pulling spark wires may injure you and not kill engine as its getting fire from burning piston carbon or red hot spark plug.
Any SeaDoo or other jetski with OEM grey tempo fuel lines will need the entire fuel system rebuilt due to known problems with internal fuel-line deterioration & resin goo clogging up the small internal carborator filters, fuel selector valve and most other fuel system components. Symptoms also include engine bogging at higher speeds (3500 rpm). Continued riding will cause carbonizing & a burned aluminum pistons and engine failure due to lean fuel/air mixtures and high combustion temps. The only solution is to replace ALL the fuel lines with standard automotive NAPA lines, clear race Fuel lines like:
http://fastflowfuellines.com/, or equivalent, rebuild the carborators with rebuild kits,new needle & seats, and replacing the fuel selector valve. It is suggested to install a clear glass marine grade inline fuel filter just before the carborators to catch any remaining debris.Yamaha also has a good i/f.
Inspect the fuel separator/filter O-ring and gas tank vent one-way check valve.
For the carbs to work, you have got to have the flame arrestor on. This is what creates resistance, along with the manifold pressure created by the compression of the engine, to get the gas to the motor. So, if you don't have the flame arrestor on, you'll never get fuel to the motor.
Gas Tank Breather Check Valves
A Hard to Start common cause is a carburetor needle(s) & seat(s) leaking fuel into the cylinders causeing a hard start condition when motor is hot. How can gas get past a needle valve other than what I have talked about? One way is if the fuel tank pressure release check valve in the OUT vent line thru rub rail is not functioning. The fuel pressure in the tank overcomes the spring tension on the needle valve and gas is FORCED past it. The valve should open at approx. 3-5lbs. psi.
