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I have a 748s chassis with a 996 transplant. Earlier this week she started but died a few seconds later and hasn't started since. If I spray some starter fluid into the carbs she'll start for a few seconds so I'm pretty sure it's a fuel supply issue and not electrical/relays/plugs. Fuel pump whines when I turn the key so I'm focusing south of the tank for now.

Now that I have the tank and airbox off I'm a little confused at what I'm looking at and the Haynes manual isn't helping. The throttle bodies have 4 injectors (green heads) but only 2 of them have electrical connections. Should I clean/replace all 4 injectors or are the 2 that have electrical connectors the only ones that are actually doing work?

Any other usual suspects that I'm not thinking of?
 

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The throttle bodies have 4 injectors (green heads) but only 2 of them have electrical connections. Should I clean/replace all 4 injectors or are the 2 that have electrical connectors the only ones that are actually doing work?
Your 996 has been converted from dual injectors to single injectors per cylinder.

All 996s came with two injectors per cylinder. Before the 996 model, only the SP and SPS bikes had dual injectors. However, those earlier bikes use the larger P8 computer which is capable of firing the injectors sequentially, meaning that the second injector sprays only at the higher engine speeds.

The 996, on the other hand, is controlled by the smaller 1.6M computer which is incapable of firing the injectors sequentially. So the engine does not run well with both injectors firing at the same time, especially at low rpm where spray durations get too short to get good spray patterns. The fuel dribbles out. In particular, this causes a roll-on stumble at 3,500 rpm that is cured by using the single injector and an Ultimap UM222 Eprom.

So, the injectors that are hooked-up are doing the work. You can test your theory that the problem is with the injectors by connecting instead to the other injector on each cylinder.
 

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open your cap and turn the key on, do you hear or see fuel spraying in the tank? if so the fuel line is split, no fuel pressure, no pressure no start. if you dont see or hear fuel spraying in the tank, that means you most likely have an electrical problem.
 
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