Carb Re-jetting
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With the vertical location of the carbs on top of the R1 engine there is absolutely no chance of squeezing the bike airbox on under the bonnet, indeed it would probably be mostly above bonnet level and perhaps even obscure your vision when driving. The new style Striker bonnet has a bigger bulge in it so at least the carbs are contained within the confines of the under-bonnet area and it should be possible to use either a foam filter or an alternative airbox.
Opinions on whether to use an airbox or
foam filter are polarised depending on whether you are a biker or a bike-engined
car owner. Everyone who races bikes or sidecars insists that an airbox is
essential to draw a good volume of cool air into the carbs. In a car install
there is less obstructing the airflow to the carbs, in fact there is nothing in
the way, so a foam filter is an easy solution, providing it is pulling cool air
in a non-turbulent location. Either way the standard airbox isn’t used and
this means that the carbs need to be re-calibrated to work with a less
restrictive air filter.
Based upon the positive experience of other R1 engined cars I decided to use the TTS re-jet kit. It would seem that this provides good fuelling throughout the range and makes good power with the increased airflow coming from the loss of airbox and also the less restrictive exhaust system.
The TTS re-jet kit for the R1 comprises a set of adjustable dynojet needles, three sets of main jets (140, 144, 150) and a bit of epoxy. I wasn’t exactly struck by the value-for-money of this kit, particularly as two of my sets of mains were obviously not new and quite dirty and there just wasn’t enough of one part of the epoxy to get a good mix.
The instructions are very simple, but then the job is fairly straightforward if you have seen it done before. I expect that I would have been on the phone a lot if I didn’t know what the basic parts of the carbs were.
First thing to do is remove the black plastic covers from the slides and carefully remove the slide and diaphragm. The needles are held in by a small grey plastic widget which you pull out with a pair of long-nose pliers. Then out come the standard needles. Remove the plastic spacer from the needle and retain for use on the dynojet needles using the new e-clips and washers in the same place as the originals. The instructions recommended putting the clips in position 2, which is one down from the top. With the slides out it is necessary to block one of the two air holes with some epoxy. When this has cured the whole lot goes back on as it came off using the standard springs.
To swap the mains simply remove the float bowls and unscrew the standard main jets – my originals were 130s and the instructions said to put 144s back.
It is also necessary to block the main air jets with some more epoxy. The instructions said to remove the bellmouths from the top of the carbs to do this. I followed the instructions and found the brass screws holding these on to be very tight, they were loctited in, and obviously not really intended to come off. I found it necessary to remove the rubber trumpets, they just pull off, to get a good purchase in the screw head and despite this still managed to round off one screw head and sheer another one off, one of which was so tight that it would not unscrew at all with a pair of pliers and sheered off again flush with the carb body thus needing to be drilled out and re-tapped. With hindsight it is possible to access both the main air jet and pilot air jet through the slots in the bellmouths and I would have tried to block the main air jet up through this slot. The instructions give no clues as to which is the main air jet, other than it is brass. It is in fact the smaller of the two which does not unscrew. The bellmouths were replaced with new screws which were loctited back in and the trumpets reattached.
I guess time will tell how good the needle height and main jet size is and now that I know what I am doing these can be swapped within a matter of minutes, without needing to be removed from the engine.
Once the carbs were fitted it was possible to stick the bonnet on and see what sort of clearance there was under there. At first the throttle linkage is preventing the bonnet from going on properly, but with this removed it went on OK. With the bonnet on it was clear to see that there is no clearance whatsoever under the bonnet. The trumpets are very nearly touching the underside of the bonnet as are the sides of the carbs. Probably a good job I did manage to move the engine inboard by a couple of millimeters otherwise the carb bodies may well have been touching the bonnet too. I had wanted to try and avoid a hole in the bonnet and was intending to fabricate some kind of airbox in the underside of the bonnet bulge. However this is not going to work now as there is no clearance at all between the bonnet and trumpets. I'll have to cut a hole for a foam filter or have an airbox that protrudes through the bonnet. I did find an interesting airbox made by plays-kool, who are now Sylva agents. This airbox looks like a copy of the SBD one and is probably too big, but I think that it fits over a Pipercross PX600 filter so would be a possible add-on at a later date. With the airbox on top of a foam filter it would provide a fairly effective ram effect, but might look a bit stupid. May give this some thought later.
After a bit more thought I decided to shorten the original bellmouths by removing the rubber trumpets and getting the alumium casting turned down flush with the upper surface with a small radius on the inside to smooth the airflow. I got this idea by looking at the QBCarbon website at all the goodies they do for R1. On this site is a set of replacement high flow trumpets that are basically shortened versions of the originals. These also claim to add a couple of horsepower too with the improved airflow. I also spoke to Ray Stringer who basically make the same items from original bellmouths and if it is good enough for them.
So it now looks like I will be able to use a foam filter and keep it under the bonnet with no holes to spoil to clean lines of the car.