I’ve never been completely happy with the Weber setup I have, its been very hard to get it properly tuned here in the Netherlands, there are not a lot of rolling roads available, and prices are expensive, also each change requires new jets, and associated fittings, the cost of this adds up very quickly.
When I first fitted the carbs, I let Speed On fit the jets and adjust the pressure, this resulted in an idle of 2000rpm, air leaks, and fuel pouring out of the rubbers. I then fixed the mess and fitted smaller idle jets which made it more drivable. From there I went to Hot Rod who spent a few hours balancing the carbs and adjusting the jets, however its still not quite on.
- At idle, the fueling is very rich, this results not only in a bad smell
- At sustained high RPM (IE Vmax) I get fuel starvation at around 200kph, this is very inconvenient, although more related to the fueling setup than the carbs.
- There are a few flat spots and it does bog down quite a bit accelerating from low RPMs at medium to high engine loads.
- Fuel economy, now whilst I didn’t buy a car like this for its fuel economy, I’m getting somewhere between 11l/100km cruising to 17l/100km at higher speeds (above 110kmh) and when driving briskly. What I’m really expecting, is somewhere in the region of 8-10l/100 when cruising and 10-13l/100km when driving briskly. Its a light car, albeit not a very aerodynamic one, but should be capable of good fuel economy. This is also represented in the performance. David Ashurst is getting 150bhp at the wheels from his cross flow, he has a much more larey camshaft, but similar sized cylinder head. My setup should be capable of around 130hp with proper fueling, so I’d like to get this sorted out.
Subsequently it is time to go fuel injection, whilst in theory there should be no difference between carbs and fuel injection as far as peak power is concerned. FI has significant advantages over traditional carburation.
- Air/Fuel ratio can be altered electronically, this makes tuning much simpler, rather than have to order jets, fit them, test them, and order more new jets, I can simply adjust a setting in software.
- There are a plethora of settings on a DCOE all slightly related to each other, and all with a profound effect on fueling and performance, however ultimately a carb is a huge compromise. There are three main ranges of adjustment, Idle, Progression, and WOT, at the ends of each phase AFR tends to be far from perfect. FI will provide much more fine tuning.
- Fuel economy can be improved in a few ways with fuel injection, for example by cutting the fuel on over run.
There are a couple of logical routes to fuel injection. The two logical ones being expensive and easy, or cheap and complicated. I’ve veered somewhat towards the expensive and easy option.
Looking at a thread on the megasquirt forums, http://www.msefi.com/viewtopic.php?t=6627 detailing the various sizes of motorcycle throttle bodies, I proceeded to order a set of GSXR 600 throttle bodies, these seem to be fairly well matched, with a 45mm internal ID. I also ordered a set of mounting rubbers, these have a rubber clamp on one side and a mounting flange on the other. I’m hoping that I can mount the flanges directly to the existing manifold, in doing so I can then respace the throttle bodies out to suit.
The fuel rail is cast aluminum, so I shall cut it where required, enlarge the hole in the casting to accept a pipe, and use duraweld aluminum brazing rods to seal it up.
I will install a swirl pot on the engine bay in place of the current fuel pressure regulator, the output from which shall go to a high pressure pump, and then to the fuel rail. The return from the pressure regulator will go to the swirl pot.
I’m most likely going to use megasquirt to control the fuel system, using the existing EDIS installation that has proven to work well for ignition. The functionality provided by the megajolt will be provided instead by the megasquirt unit. I will use a throttle position sensor (TPS) rather than the Manifold Absolute Pressure (MAP) sensor I currently use.
I will also permanently fit the LC-1. I had originally planned to keep this as a hand held device, but this is needed with the mega squirt both for initial tuning, and for ongoing adjustment of the Air/Fuel Ration (AFR) as I drive.
In order to make the installation nicer, I shall cut down the wiring for the LC1 so that it is a more manageable length, however I shall leave a longish tail for the gauge so that I may connect it up to provide a visual indication of AFR as required.