Sprint 2004 Sprint 955i Holding Back

I would check the mapping using tuneecu, probably the wrong map.

 

Has it suddenly just started doing this?

 

What did the restoration entail? It seems that the bike has been idle for some time. It might be worth removing the tank and airbox to check that all of the rubber vacuum pipes are intact and that the airfilter and intake is clear. Also check that the tank vent is clear and not causing a vacuum in the tank and fuel starvation. Is it possible that the issue was already there when you acquired the bike for restoration?

 

Depending how and where it was stored it still might be worth checking the airbox for rodent nests.

 

And while you are there check the coils and leads and plugs.

 

The 955i engines are fairly robust, as the bike only does it between 2 and 3 K revs, which points either towards a faulty coil stick or an injector, given the machine was laid up for some time, the old fuel can and does congeal in the injectors, it may be slightly restricting the atomisation, hence the non-response low down the revs. My first call would be the coil stick in the centre cylinder, this is about the only real downside to this engine, the rubber retaining caps on the cam cover allow water in, degrading the coil stick, and worse still corroding the spark plug in the head solid, getting it out is time consuming along with patience. I would also check the fuel filter, as you will know having restored the bike these do require a regular change, and the gasket on the tank side retaining plate needs a new gasket each time it is taken off. A BMW replacement is cheaper and readily available. These bikes do not like being laid up for the very reason you describe, they also do not like E10 fuel.