Injection

Yager GT 50 EFI

Why Electronic Fuel Injection?

1. I do not like carburetors, there aged, and you can't propperly tune them for the whole rev range of the engine. A nozzle has a fixed size and can't adapt it self to changing circumstanses. (the weather, temperature, barometric pressure and more) Also there is no control mechanism to check if it is tuned right.
2. With an EFI you can tune everything in to detail. Pre ignition, injection time, air to fuel ratio, with a laptop. This does requires some knowlegde
3. Most of all, I like doing these sort of things.

To understand why an EFI is beter than a carburetor you need to know a few basic things.

To get a stoichiometric combustion you need to have 14.7 kg of air and 1 kg of petrol. At this ratio the petrol will be fully burnt with minimal tocxic gassen. That optimun ratio will in general never be reached, it is affected by several factors. (Throttle position, temperatur, air pressure and more).  A carburetor cannot adapt it self to these factors. If you tune a carburetor today with the right nozzle, it could all be different tomorrow due to changing weather. With an EFI the stoichiometric combustion is checked by an oxygen sensor

The oxygen sensor measures the amount off oxygen in the exhaust gasses and passes this information on to the engine ECU. With these values from the oxygen sensor the engine ECU can determine how much fuel is needed for a combustion that is less environmetel disturbing

• Lambda = 1 - optimum mixture - 14,7 kg air op 1 kg pertol
• Lambda < 1 - Ritch mixture - Not enough air, example: 12 kg lucht to 1 kg benzine
• Lambda > 1 - Lean mixture - To mutch air - example 16 kg lucht to 1 kg benzine

The EFI parts

The EFI system parts lkist

1. Engine ECU
2. Fuel injector
3. A throttle body with a throttle position sensor to read the opening of the throttle
4. Fuel pump
5. Fuel pressure regulator

The above are the minimum required parts to get an EFI working. The differences with a carburetor are small. Every value is pre fixed and it can't adapt to changing circumstances.
To be able to adapt to changing circumstances the EFI needs more info from different sensors.

1. MAP sensor - Manifold pressure sensor - measures the air pressure in the inlet
2. Air inlet temperature sensor
3. Oxygen sensor
4. Engine temperatur sensor

With the values from these sensors the EFI can adapt to changing circumstanses. The changes the EFI can do are:

1. Injection time - how long the teh injector sprays fuel in to the inlet in milliseconds
2. Pre ignition - advance or retard the ignition

This is the EFI kit I'm going to use: Small Engine Fuel Injection Kit van Ecotrons.
This conversion kit is suitable for single cylinder engines in the range from 35 to 300 cc, but is not plug and play. To get this kit working on my Yager GT 50 I need to make some modifications.

The modifications

The things that need modification are:

• An adapter between the throttlebody and the intake manifold
• Shortening the throttle cable housing at the throttlebody
• An extra outlet on the gas tank
• Oxygen sensor in the exhaust pipe
• Adapt the Ecotrons wire haness to the Yager GT 50
• Make some brackets for the fuel pump, the fuel filter en the fuel pressure regulator
• Making everything rock solid

The adapter between the throttle body and the intake manifold

I have not found anything suitable for this, so I had to create something myself. Luckily I had acces to a lathe what solved the the problem. After a lot of measuring, drawing and fabricating the adapter was ready. The inside connects seamlessly to the throttlebody and the intake manifold.




Shortening the throttle cable housing

To allow the throttle plate to fully open and close the throttle cable housing needs to be shortend at the throttlebody.


An extra outlet on the gas atnk

The fuel pump can't suck fuel, gravity makes the fuel  flow through the filter in to the fuel pump. Because of this the fuel pump needs to be lower than the gas tank. An extra outlet needs to be welded in to the botom of the tgas tank.
The old outlet on top of the gas tank will now serve as an inlet for the return fuel from the pressure regulator. When the fuel pressure is more than 3 bar the pressure regulator will open and let the excess fuel run back in to the gas tank.

Oxygen sensor in the exhaust pipe

With the kit comes a bung, this bung needs to be welded in to the exhaust pipe at aproximatly 10 to 15 from the exhaust port. The oxygens sensor will be fitted in the bung. The tip of the oxygen sensor is now in the exhaust gassen where it measures the level of oxygen.
The sensors only work effectively when heated to approximately 316 °C (600 °F). This temperature gets reatched with the help of a heating element and/or the exhaust gasses. The element heats the oxygen sensor after start and keeps it at the required temperatuur with the help of the exhaust gasses. Placing it at 10 to 15 from the outlet port helps the heating.


Adapting the wire harness

The wire harness that comes with the kit is made for a specific bike. Because my parts are further away or in a different location I had to shorten or extend numerous wires.

Fuel pump fittings

The fuel pump has to be mounted below the gastank, to achieve this I had to make 2 brackets and weld them to the frame. The fuel pump is now in a very hostile inviroment, water, sand and salt are thrown up by the front tyre and end up between the gastank and the underbody. To shield the fuel pump from this I fitted it inside some pvc tubing. The fuel filter is accessible by removing the under body.

The installing

Disspite the long preparation you still will encounter problems when you finaly install the kit.
After I mounted the throttlebody I noticed that the iron bend part at the end on the throttle cable was resting on the chainbelt tensioner bolt. After mounting longer stud bolts and 2 isolators ( the black disc between the cylinder head and the intake manifold) I had enough clearence.
Because the engine moves in relation to the frame I wanted to limit the strain on the injector caused by the movement of the engine. The injector is very small and made from plastic.
I made a bracket on the stud bolts and made a brass pipe that connects the fuel hose comming from the injector to the fuel hose fixed to the frame.

The brass pipe absorbs all strenght due to movement of the engine.
I also sealed of the two vacuum intlets on the intake manifold.

I placed the engine ECU on the bracket of the original fuel pump and made a bracket to hold the wire harness. This bracket also hold the oxygen sensor connector (white connector), fuel pump relais and a bluetooth module (black box with the gray connector. When paired with an android device (phone or tablet) I can read and record what the engine is doing and make adjustments to it. To read and adjust the recorded values you need a program called ProCal.

The original map sensor broke pretty quick, I replaced it with one form VPV racing  and mounted it on the underside of the luggage compartment.

First start

After bleeding the fuel line, checking for any leakage and all connections it was time to fire it up. sadly I do not have this on film, but it ran at first try. At first idle was to low to keep the engine running (1000 rpm) but after adjusting the idle air screw it now idles at 1400 rpm. At first drive a few changes were noticable. Up hill I gained a few kilometers, going from 43 kmh to 47 kmh and I had more top speed.
With the carburetor my top speed was 61 kmh (55/56 kmh on the gps) and I never reached the revlimiter. Now the engine reached the rev limiter (8000 rpm) at top speed (64 kmh - 58.7 kmh on the gps). That is a little bit to fast. In the Netherland the legal speed limit for a 50cc scooter is 45 kmh. Between 46 and 56 kmh you get a ticket and at 57 kmh and above your vehicle registration will be suspended. I don't want that so the rev limit has to be lowered. I am now at 7750 rpm and have a topspeed of 61/62 knh (55 lmh on the gps).