rusefi.com

I'm looking at converting my 1994 BMW F650 motorcycle to EFI using RusEFI (probably a Frankenstein), I had planned on using a MicroSquirt but this looks to be a far more affordable choice and better since I'd be far happier with proper open source hardware and software

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

Welcome!

I am afraid that the answer for most of the questions would take actually trying, at least I definitely do not have most of the answers. I can comment on the software and confirm that you can have two channels with same exact signal in case of a one-cylinder.

Thanks for your response. Even though a lot of what I'm doing is going to be a learning process, I think I'm going to try and see how I get along, none of the components are going to be too expensive for an experiment, and I'm at my wit's end with these carbs, which I now need to strip and fix a fuel leak on AGAIN.



This is the video posted by the only person I know of who did an EFI conversion on this vehicle so I'm looking carefully for any details I can spot. He's really bodged the throttle body on there, I hope to get a more 'oem' look but I think I will probably go for a similar arrangement with regard to the coolant sensor and lambda placement although I think the fuel pump he used is about 5x the size it needs to be 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.

Is that 4 stroke? I would expect problems with 2 stroke as they dump lots of oil, which I would expect would bugger a WO2.

Do you have a schematic for CDI? I believe we have a russian kid who's done a CDI moped. So it might be possible, but I would need to learn more about the circuit before I can really tell you much.

Physically we can do 2 outputs both ignition and fuel. I believe staged injectors is planned for, but hasn't been implemented yet. So you may be able to use large injectors for WOT and full load, then small injectors for smooth idle.

Using a large carb as your throttle could cause problems regulating air flow at idle. You may want to plan for some kind of bypass if you can, but with EFI I would think there is a good chance you can do it with out it. You might get by with regulating fuel.

With the low inertia on these bike engines, I would suggest more ticks per rotation than 1, but you can probably do OK with only the 0 tick. I do not know how well the software is developed for this though. If you can install a 36-1, or similar wheel, that would likely be easiest from a software stand point, and you'd be using software that has been better tested.

It's a 4 stroke. The engine is a Rotax 654 which is a 649cc dohc 4v single. I believe the Aprilia throttle body pair I mentioned are an identical set, there's no staging of fuelling or the throttle butterflies but I'm definitely erring more toward doing it with a single throttle body for simplicity of wiring and weight. I can just use the one from the later BMW 650GS, which uses a mildly re-engineered version of the same engine making around the same power (only ~48 bhp) so it presumably has close-enough flow characteristics and has IAC.

Azurael wrote: 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!

I think the problem with a MAP on a single is that you get very strong pulses when it draws fuel in and nothing in between. I have been giving this some thought as I have been considering injecting my XBR500 engined race bike. I wonder if the solution is to synchronise the MAP reading(s) to engine position. At present the bike is in pieces scattered at three different locations, I was intending to get it running on the carb and take some measurements from a MAP to see what the waveform looks like.

Speaking of MAP rusEfi has configurable map averaging window and sensor sniffer is our build-in tool to look at the MAP wave.