Thursday, 27 August 2015


The project came to a bit of a halt over the winter and spring due to the unexpected rebuild of another bike. Now though it is slowly coming back into line.

While I have not started the bike in months and progress would appear to be slow from looking at the semi-naked bike in the garage, some good and very important steps have been taken towards making sure the EFI system is fully integrated into the bike.

Firstly is wiring. During the early calibration and testing stages, I still had not fully finalised the wiring loom. While the EFI side of the loom is good and did not need to be touched, the auxiliary loom which forms part of the Koso dash installation had not been finalised. I pulled out the dash loom again and split it into two definitive sections which allows the dash to sit much better when the nose fairing is installed. One section feeds into the original loom via one of the original clock connector and the other which routes down the RHS of the bike taking the constant power source & fuel level signal to the dash. CLT & speed sensor wiring was also plugged into this side of the loom and I integrated the Eclipze headlight upgrade wiring into the auxiliary loom also.
That bit of tidying has fixed some items which I was not 100% happy with.

Revised Dash Harness Routing

The second and most important thing was to permanently turn the carburetors into throttle bodies. When I first fitted the throttle bodies I was unsure if removing the slides completely would cause issues with response & rideability at low throttle openings given that the throttle bores are so large in comparison to the inlet ports. In order to verify this, the slides were simply held in their fully open position using silicone sealant to test the rideability. During testing, no adverse characteristics were noted so the original plan to bond the slides in place permanently was carried out.

The slides were each filled with reinforced epoxy resin and bonded in the fully closed position with the same epoxy. The main slide area was then cut out using a dremel tool and cut back to meet the throttle bore wall. A brake cylinder hone was then used to grind any imperfections down and ensure bore roundness was maintained. After initial honing, epoxy resin was reapplied on any low spots and the honing procedure repeated. Once a good finish was achieved with the hone, the bores were finished by working up to 800grit emery paper. Right now, the gas path is smooth all the way through the throttle body with none of the imperfections of the carburetor left to disturb the air.

Epoxy Infill After Roughing

Finished Throttle Bore

I was not 100% happy with the injector testing which I had carried out before. Only one injector had been tested, the flow rate was a little approximate and the dead time calculations had been inconclusive so that my current calibration still contained the default figures. Getting the injector dead times right is crucial to a good idle, especially as the injectors are still a little on the large side for the mc22 so I opted to retest all four injectors using better equipment.

Short lengths of flexible tubing were slipped on over the end of the injectors to direct the flow and also to minimise vapour spray. The injector being tested was fired into a plastic container which was placed on a scales. Weighing the fuel injected was far more accurate than measuring it from a graduated cylinder as larger quantities of fuel could be used for the test and thereby minimise the effects of any errors in readings.

A variable bench power supply was used to power the ECU & injectors which allowed dead time tests to be conducted at 3 different voltage points and measure dead time variation with voltage. The fuel pump was still driven by the battery as the power supply did not have the current rating to support the fuel pump power demand.
Each injector was tested at 100% duty cycle for several periods of 1-2mins to get an average flow rate. Dead time tests were conducted using 10 different pulsewidths at 3 different voltage settings, with each data point test timed to last 2mins. This resulted in long test times although confidence in the results is very high.

Measuring Injector Discharge

Test Bench

Test Results

The fuel line fittings are also being upgraded. The initial testing was carried out with a standard steel banjo fitting feeding into the end of the fuel rail. A fibre reinforced fuel line had to be used due to space restrictions not allowing an aeroquip hose to bend around to meet the fuel pump. Space was also so limited that the banjo bolt fouled on the frame with the throttle bodies fitted. It was good enough for early testing but certainly not good enough to stay that way.

One solution was to cut 2-3mm from the end of the fuel rail and to shorten it. However, an alternative banjo fitting had to be found anyway to route the fuel pipe to the pump so modification of the fuel rail was held off until suitable fittings could be found.

Luckily enough, the good people at ATEC Autotechnic make a selection of quality motorsport grade fittings and will supply CAD models of everything on request. That allowed the packaging to be determined before buying and it was found that by using these quality fittings, the banjo stack height could be reduced by over 3mm meaning that no fuel rail modification was needed.

New Fuel Fittings

Old vs. New


  1. Congratulations. That's a well executed conversion! We have discussed briefly at the MSRUNS forum and I've been following your progress regularly. Why didn't you use the GSR400 TBs? Too much trouble to get them to fit properly may I assume?


  2. Hey! I've just realised I never replied to your query! Sorry about that. You hit the nail on the head though with the GSR TBs. The spacing was wrong with them and to get them to work properly I would have needed to make new butterfly rods as well as cutting & fabricating the castings. It was far cheaper and easier in the long run to modify the original carbs.

    Saying that, I'm not 100% happy with the modified carbs route. They are much bulkier and heavier than they need to be so I will be manufacturing a set of throttle bodies to replace the carbs at some point down the line. Not anywhere in the near future though.

  3. If you don't have any use for the GSR400 TBs and consider selling, drop me a line. I don't know how much of a direct fit for my GSF400 these may be, but I have the same issues as you with the modified carb bank. It may worth a try...