The closing of 2017 saw the very first Transfer Port Injection 2-stroke motorcycle roll off the production line in Austria and onto dealer floors in what would be a world first…or would it? Could it be that a back-yard shed, deep in Waikato farming country, in 2012 be the actual birth place of TPi? We made a plan to find out.

Words: DRD | Photos: Supplied

Sometimes you stumble upon interesting information by sheer chance, sometimes you head out searching for it and other times it finds you. This was a case of all the above with regards to Transfer Port Injection – which from now on, we will call TPi.

Neil Hintz is an engineer, cum dirt bike enthusiast, cum serious microlight engine builder. His back shed is larger than you would expect, with all manner of engine, transmission, lathe and CNC machine lying round. He is also into casting his own engine cases, but that is a complete other story. What interested us the most was his claim that he in fact, invented TPi and installed it into a YZ250, back in 2012.

You might remember his injected Kawasaki F9 from last month’s magazine. That was Neil’s first foray into the motorcycling engine-injection business, which saw him meet with many obstacles, but ultimately led to success in a very old platform. It was a chance encounter at a trail ride that saw Wayne Blackwood from Blackwood Yamaha notice the F9 first-hand. Shocked at how well the old girl went with the injection system, he wondered what it would be like in his own YZ250.

Neil and Wayne made a plan to come together and sketch out a blueprint that would inject a 2012 YZ250 2-stroke right through the transfer ports, just like KTM and Husqvarna do it today.

In 2013, this was proven true on many different trail rides with the TPi YZ tested back-to-back with Neil’s standard carburettor YZ. Same bikes, same pipes, same reeds, everything the same; except for the fuelling system.

“We would fill the bikes and then go out and do a 30-odd kilometre ride, fill the tanks again, swap riders, repeat. Many rides were tested like this and the outcome was interesting. 14% savings if the track was open and fast with an impressive 21% fuel saving on the slower more technical tracks – much like we expected.”

It is also interesting that early on with this testing, no dyno time was used and it was just all seat of the pants tuning to get the fuelling system working right.

“I’m sure we could have had even better results with at least some test gear and it just goes to show how easy this system is to tune.”

A few months later, both bikes saw the dyno, with a very similar top end power output. But in the mid-range, the TPi didn’t have the same punch. With it being much smoother in the torque delivery, it had an almost ‘gutless’ feeling in comparison to the carb YZ.

“But the hard fact is, if you want to ride fast, the TPi is much better. Better control, better traction, just better all round. Less time reigning in slides and general uncontrolled wheel spin as on my normal YZ. It was very noticeable. It can lay on its side for as long as you want and start first kick with no flooding. In fact, it’s fitted with an auto clutch now so, as long as it’s getting fuel to the pump, it will just lie there and idle. But why is it laying on its side you ask? That’s just my riding.”

World ‘Release’

Late in 2013, a picture of the TPi YZ cylinder sitting on his work bench was released in a German dirt bike magazine, with some speculation as to whether it might be a secret Yamaha development.

“Ha – it wasn’t hard to tell it was my work bench by way of the Autogyro rotor head parts in the background. There were pictures being distributed of what I had already coined “TPI” on various websites here and around the world by this stage, with a lot of dialogue as to how it all worked with the hope that some manufacturer might run with it. There is a lot less of a story to accompany the TPi YZ unfortunately, as its development went so smoothly. After all the headache of the original Kawasaki F9 development, we were already half way there before we started, so you learn as you go I guess.”

The YZ project started in 2012 with the casting/machining of throttle body parts and modification of the original YZ cylinder to accept the injectors and the fuel rail around the cylinder – 6 years before the release of what you can now see on the KTM/Husqvarna set up.

“By March 2013, we had completed the hardware and ran the TPI YZ for the first time. I loaded my Kawasaki F9 program into the YZ’s Link ECU with a slight change to run it on petrol rather than the ethanol the F9 runs on.”

Within an hour of round the back yard riding Neil and Wayne had the tuning dialled well enough to take it out on an Epic Events trail ride on May 2013 for the YZ’s first official test.

Visit YouTube and search for the account GerbilGronk and check out the video of the first TPi YZ getting tuned around the back yard and its debut at the Epic Events trail ride.

“We rode the YZ on many rides in 2013, finishing up with the Acerbis Four Hour at the end of the year – it’s first competition event. The TPI YZ has completed the 2014, 2015 and 2016 events also, with development so low key (never needing to plug the laptop in) that not one person noticed this most unusual YZ circulating the pits.”

After the initial fuelling system was finalised, a bit of time was spent trying to work out a suitable oiling system. Turns out all that was needed was an old school auto lube, ironically.

“We ended up running a small solenoid-operated jet into the drum throttle body, supplying two-stroke oil. Under 60% throttle, it shut off. Over 60% throttle, the jet opened for business. A very crude way of doing it, but it seemed to work well enough with no big end or piston failures to date.”

The similarities between Neil’s design and the TPi found on the new KTM/Husqvarna are eerily similar. Neil admits that he had no patent on his idea and that it was never something he wanted (or would have been able) to keep to himself or make money from anyway. Something that suggests some truth of this situation is that Husqvarna has produced a short video, explaining exactly how its TPi system works for the world to see. Surely, this is something you would expect a large company like that to patent if it was 100% their own innovation?

“TM contacted me in 2017 to ask for the rights to my TPi patent after first seeing it online, and then on the new orange bikes, but I had to tell them it was free to all. It doesn’t bother me if they did copy my design, I just would have loved to have been part of their process. This stuff really interests me; the 2-stroke still has a lot to offer, especially once fuel injection is involved.

All this has led to a new development using a modern alloy, YZ250F perimeter frame fitted with a water-cooled, 360cc rotary-valve engine, (Neil’s favourite kind of engine), running a newer version of his TPi design, which should provide even better results in terms of power delivery and fuel economy.

“This is still in the works though and something I will be keeping to myself for now I think. Perhaps it will run in this year’s Acerbis Four Hour. At least, that’s the goal.”

“Wayne sorted the charging system, a YZ450F flywheel and stator” Neil explains. “I organised the injector placement and an induction throttle drum to replace the carburettor.”

It became apparent after some initial fiddling that the injectors needed to be in the ‘B Ports’ and aiming toward the incoming air that travelled up the transfer for the best mixing.

“This also has the added advantage of a place to store the extra fuel when the injector ‘on’ time exceeds the port open (or at least flow) time. It also is apparent that at high engine speeds, there is some fuel that finds its way into the ‘A’ ports. This makes for excellent homogenisation when running up on the pipe.

“At lower engine speeds, however, where raw fuel is traditionally lost out the exhaust port, partly due to the ‘A’ port’s proximity (right next door to the exhaust port) and partly because of the relative long port duration time available with minimal gas inertia, the fuel spillage is greatly reduced due to the ‘B’ port (where the fuel is introduced) being so far away from the exhaust port.”

All pretty technical stuff that was all thought out and tweaked before a single barrel was harmed in the process and which, in layman’s terms, means the engine is far more efficient, introducing fuel via the ‘B’ port over the ‘A’ port or the traditional carburettor.

THE WORD | Wayne Blackwood

The other piece to the TPI puzzle, Wayne Blackwood of Blackwood Yamaha, had the bike and the enthusiasm to make a great team with Neil.

DRD: What was the initial idea behind it?

Wayne: The idea came from Neil’s F9, because he spent a bit of time developing that and nobody even noticed, so he wanted to do something a bit more modern so maybe people would see it and wonder what was going on there. But again, no one really noticed.

D: Was it a reasonably straight forward build as far as you expected, when you’re doing something so cutting edge.

W: Yeah, yeah it was. Getting things to fit in there was a bit of a challenge, just physically getting the components where we needed them and still not making it too ugly or too big. Because of the two computers we ended up having two pickup coils so we just stacked another one up outside the flywheel on a little trigger plate. But now, with the newer computers available, we could probably do away with that and just run one pickup which would be cleaner. You can see the injectors here. There’s the custom-made throttle body we had made for us too. We could have just used a butterfly throttle body off something without the injector in it because we weren’t running an injector there. But this way, you can see there’s no restriction on airflow, there’s no butterfly in there, it’s a nice and clean intake, ‘cos that was something we were keen to try. So it’s a drum-type throttle position sensor on the side, and the injectors going down into the transfer ports.

D: Does it add anything in terms of weight to the bike overall over the ‘carby’ version?

W: Yeah, it added a little bit of weight. We’re carrying a battery on board – a small battery – and a fuel pump, but that’d be the only added weight.

D: Did you find the TPI much better than the carburettor?

W: Just different. No more horsepower or peak horsepower, but much more linear in the power delivery. No traditional 2-stroke surge, well not in the same way. It seems to be a bit more controllable. Right off the bottom, I don’t think it seems quite as sharp as the carburetted one, but much cleaner. Like I say, you could stall it, tip it upside down, fall off, pick it up, kick it and it would run clean straight away.

D: Would that delivery help in your traction as well – not being so aggressive and help you on a hill that’s a right sod?

W: Definitely. So that’s where we want to go next. I like 2-strokes, but the power to the rear of a 2-stroke is not good for fast lap times when its slippery. It’s hard to control, so this way we should be able to tune the engine for higher horsepower and still have it ridable. With the electronics available, we might be able to and we’ve got some ideas about putting traction control in it.