Fuel 'Primer', a Rotax 447 question
Connect your plunge primer fuel supply direct to its own dedicated pipe from the tank, not the main feed line, because if/when its own valves inevitably start to dribble it won't compromise the engine's suction feed.
My 1990 S4 was fitted with a plunger type carb. enricher fed via a Tee'd plastic pipe off the main fuel delivery line. Never constant it also bled fuel forward when squeezing the delivery primer bulb. I removed it completely to reduce the risk from its thin pipe for leaks. You also lose a few ounces weight. Full choke & closed throttle with prop hand turned 20 times is my method. Vince 'primes' the carb by blowing down the float chamber equalising pipe at its brass centre connection to atmosphere. I do it too as it's a magic method when cold.
Fuel feed failure risk. The squeeze bulb fuel pump 'prime' internal non return valve can also risk in flight feed blocking. Fitting a by-pass fuel tube is said (see below) to be a solution To feed fuel before starting, simply pinch the tube whilst squeezing the bulb.
The squeeze bulb is a primary and essential part of fuel delivery system. Black and gooey stuff from the pipes is not. I found my bulbs would do this and also crack on the outside and the ends would pop off on one of them, not to mention the valves malfunctioning as well.
After discarding it there was no more gunk in the filter and all the fuel lines stay the same colour without the blackening they used to get.
Another sign of the black rubber disintegrating is the change in colour of the fuel lines. Seems the premixed fuel might eat the rubber stuff up. Some bulbs are made out of oil resistant materials but they don't have labels on them. I now use oil injection and put a Facet electric pump in place of the bulb and the problem is now gone. I switch on the pump while starting then turn it off. Can always be used a emergency pump if the Mikuni gives up."
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