This is a single cylinder water-cooled engine, and I had a few questions regarding specifics - I have had a look through the wiki to see if the answers were there but apologies if I've missed anything obvious.
Firstly, this engine as standard has 2 Mikuni (nightmare) carbs which are the main inspiration behind this project. I think the reason they went with a twin-carb setup on a single cylinder engine was to keep intake velocity high for good fuel atomisation at lower engine speeds, with this in mind and not being an issue for an EFI system, I think I will go for a single larger throttle body and eliminate the stock space-wasting air-box for my EFI set-up. The same Rotax 654 engine is used in a Bombardier quad (I think it's called something like a Can-Am 650?) and it looks like its 1-into-2 intake manifold should bolt straight on to my engine to minimise the need for fabrication.
As an alternative I could use a pair of throttle bodies from a later Aprilia Pegaso 650 i.e. (pretty much the same bike but with a 5v, single-spark variant of the engine but made for longer so it developed EFI later in life), which I believe would fit straight into my existing intake manifold, but I assume that having two TBs on a single is over-complicated from a set-up point of view and the bodies themselves look very primitive - they use a fixed idle adjustment (i.e. no computerised idle control) for one thing. If anybody had any specific recommendations for what would work best, I'd love to hear them.
Secondly, as far as ignition goes, this bike uses a CDI driving a pair of coils (it's a twin-spark) and I'm totally unsure what to do here. Ideally, I'd like to be able to drive a pair of plug-top coils and eliminate the HT wires - is this feasible using a single channel or multiple channels on Frankenstein? Which triggering set-up will work? I've read that big singles like this fluctuate a lot in speed during the 720 degrees of rotation between combustion events, so the most accurate set-up possible is essential - I guess a 36-1 trigger wheel mounted on the crank would be the best idea? I think I can manage to 'bodge' a hall-effect sensor under the cover at the alternator end of the engine. The one existing conversion I know of using this engine (with MS) was using the standard CDI pickup (once per rotation) and the person who did it appeared to be having great difficulty with the accuracy of the trigger. On an unrelated note, would I be able to drive two coils separately, since I seem to recall that in Alfa twinspark engine with a similar head design (one spark central, one off to the side between the intake and exhaust valves) actually runs a slight delay between firing the two plugs which helps to ensure complete combustion?
Finally, I've read that sensors in general can be a nightmare on singles due to the huge gap between firing pulses. Does anybody here have any experience in such matters? I had hoped to be able to use a wideband and a MAF to DIY tune it but that won't work very well if I can't get a stable readout... I think the guy who did the conversion with MS ended up using pure open-loop Alpha-N with only TPS-based maps, I'd like to do better than that!
Sorry if this post is a bit of a ramble, and I very much appreciate any advice you sages have to offer
which seems a bit foolish with only 280W to work with (actually, I can replace the alternator windings using parts from a later BMW 650 GS if I need more power) It's a shame the web link is long gone and I can't seem to get in contact with this person to find out a few more details though.
