Austrian reader Wolfgang with his special brew bike!
Pop the Kettle on and we will tell you about one Austrian’s amazing cross between a Suzuki GT750 and a Bimota HB1.
It’s fair to say that Bimota’s HB1 has always been one of Wolfgang Hromada’s all-time favourite motorbikes. Recently the 58-year-old sales director from Vienna made his dream come true – he built his own interpretation of the HB1 in a Bimota-like chassis and Suzuki’s seminal GT750 Kettle engine. Wolfgang admits: “Since I was a teenager, I was always swimming (or should I say riding) against the mainstream in regards to motor vehicles. While my friends in the 1970s all had two-stroke mopeds like KTM, PUCH, Zündapp etc. and sometimes reached the-then magic 60mph mark, I had to have a four-stroke Honda SS50Z; hopelessly slower on flat terrain, but leading the pack when it went uphill. When we grew older and got our motorbike licences, my friends exchanged their mopeds for four-stroke bikes like the Kawasaki Z650, Honda CB500 and the like; I had to do the opposite of course and got myself a 1976 Kettle, Suzuki’s water-cooled, three-cylinder two-stroke bike. It was not necessarily my plan, it just happened when this bike was offered to me in 1981 at a fair price. Today, 37 years later, I still have this bike. I fully restored it in 1999, and still ride it occasionally.” Over the years, Wolfgang bought other bikes depending on his financial situation (sound familiar?) but he rarely sold any on, so he was able to keep most of them. He says: “As a result, I have a collection of 20 motorcycles currently, each either in very good original condition, fully restored or customised to my tastes. The range is from 50cc to 1100cc, from 1971 to 2003: half of them being classic two-stroke bikes from the 1980s.
“One of these customised bikes is my Bimota Suzuki GT750B. For me Bimota’s HB1 has always been one of the most beautiful and desirable motorcycles. For obvious reason (only 10 have been built), it was always unaffordable. At least, my bespoke GT750 already had a typical Bimota-style seat unit with the duck-tail 30 years ago. “My dream of owning one of Bimota’s classic models goes back much longer than the 10 years that I had a GT750 spare engine, ported to TR750 specs, laying in the corner of my workshop/garage. I purchased it from a chap in the UK, and I had plans to build a cafe racer one day. I had already purchased an extra complete GT750 donor bike minus engine as basis for my build soon after. “Over the years, I hunted for suitable components to improve on the Suzuki’s outdated technology to something more exclusive and better performing. So ebay and similar sites were perused at night and I purchased a 38mm fork front-end, 18in wheels and brake discs off a Kawasaki Z1000J plus some other accessories for the planned cafe racer project. “Then, one day, it must have been in 2014, I was sitting with friends over some refreshments at my favourite place, Schwammerlwirt in Vienna (this would translate to something like ’The Mushrooms’). One of my friends told me about a Serbian guy who builds beautiful carbon body parts mainly for classic Laverda models, but he obviously had also built a tank and seat unit in exactly the same HB1 style recently for a project bike in the US. I am not sure if it was the beer which accelerated my decision to build an HB1 replica with my Kettle engine instead of a typical cafe racer, but I immediately had an exact picture of the finished bike in my head. My brain at that moment was already in a state where it could hardly formulate complete sentences, only able to see pictures, but this immediate decision I would never regret, it just hit me like lightning! “My new plan was to build a HB1 replica, as close as possible to the original, using components from that era and possibly avoiding modern technology. A bike that could have looked the same in the early 1970s. “I started to ship my spare GT750 frame, front-end, an aftermarket swingarm, wheels, an HB1 tank cover as a template and an empty engine to a Gerard (aka Jerryt) in The Netherlands, who builds beautiful custom chassis and bodyparts in steel and
alloy. I included sketches with dimensions of how I wanted the frame to be modified to mimic the HB1 chassis. Jerry looked at it, placed the tank cover on the frame and realised that the most typical design element of the Bimota, the contour of the tank with its continuation in the frame down to the swingarm pivot point, was not easily achievable by just modifying a stock frame. So he proposed to build me a completely new frame and swingarm, in exact Bimota HB1 style, to accept my GT750 engine and the Z1000J forks that I still wanted to use. To my surprise, the price he was asking was more than fair, so it took me only a few seconds to happily agree to that plan. “During the following weeks, I regularly received pictures showing the actual state of my build, so that I could address any potential changes if needed before Jerry continued with the next steps. I saw how more and more tubes were bent, cut, milled and welded around my engine, keeping more or less the Kettle’s original geometry except a steeper steering head and different swingarm pivot position. Using the tank cover as a template, the frame exactly matched the tank, which is quite the opposite of what other people would normally do – usually the frame comes first, and then the tank is made to match it. “The swingarm incorporates an eccentric chain adjuster and the swingarm pivot has moved a bit forward, closer to the sprocket to reduce the impact of chain tension on the rear suspension. The original HB1 frame used the engine as a stressed member and had no lower subframe. I did not want to put that much stress on the old GT750 engine since I did not know if it was designed for this, so I had separate detachable lower frame cradles produced, which were powder-coated in black later, so that they optically almost disappear on the finished bike with the red frame. “After eight weeks, I received the completed frame and swingarm back home in Vienna. During the following months – my job only allows me few hours here and there to spend in my workshop – I completely disassembled the engine to check everything, replace all seals and gaskets and had the crank inspected and new crank seals installed. I just did not want to rely on an engine that was sitting on the garage floor for over 10 years and which I had
not built up myself. I replaced the original head gasket with a copper gasket and exactly matched the combustion chambers in the head with the cylinder bore with my Dremel. All engine parts had been vapour blasted, and then either painted or polished. “Fitting the aftermarket Mikuni VM34 carbs was a challenge too. The float bowl of the right-hand carb was resting on the clutch hump of the upper engine case, so I had to find slightly angled carb boots to clear. Most of the required smaller parts like collars, eccentric swingarm adjuster, rear brake caliper adapters etc. I fabricated in my own little workshop, while more complex parts like the upper triple clamp or the front caliper adaptors I outsourced. The wiring was completely built from scratch, and most electric parts like battery, rectifier/regulator, starter relay, ignition switch are located in the triangular space above the swingarm pivot to keep wires short and reduce electrical losses. With the battery, I didn’t use period-correct components: I actually put a modern Lifepo4 battery pack into the empty shell of a classic lead-acid battery, to save weight and keep the battery small (the original GT750 battery is a very bulky and a heavy 14Ah type since it has to supply the electric starter). Wherever possible, I tried to use original Bimota parts, but I only succeeded with a pair of clip-ons and the rear-sets. “For the exhaust system, I knew from the very beginning that it had to be a three-into-three system, in black. I decided on a set of Jemco exhaust pipes from Texas. When I first started the engine with these pipes on, it sounded as if there were no pipes on at all! These pipes have pretty small integrated silencers, and they sound as if there was no muffler at all, creating a very loud crackling sound: impossible to ride in civilised areas in Austria, I would get arrested immediately! On the other hand, they look the real deal and are a perfect fit to the bike. So I put them away on storage for some club events or track days where the noise level would be accepted, and ordered a second set from Jemco, but this time without any silencers. I designed my own version of the silencers by use of simulation software. They are 20mm larger in diameter and 50mm longer than the original Jemco mufflers but brought the exhaust noise down to almost stock level. “I always hate the oil leakages at the header flanges of every aftermarket racing exhaust system I used till now; I did not want to accept this on my Bimota/kettle, so I had adapters machined that were welded onto the header pipes of the Jemcos and now accept the original GT750 exhaust clamps which bolt to the cylinder, they are 100% tight now. I also welded bungs for EGT (exhaust gas temperature) sensors on the headers, and I use these sensors when dialling in the carbs on the dyno. Once all work on the pipes was completed, I had them Cerakoted in semi-gloss black. “Brakes? Well, classic Ap-lockheed brake calipers secure more than adequate stopping power; they bite into cross-drilled and skimmed brake discs off a Kawasaki Z1000J. The front brake pump is also a classic Ap-lockheed: the rear is from the same Kwak model. The classic Z-series models also contributed with the control switches left and right; the tach is
the original GT750 instrument, I replaced the dial face with my own design, with a Bimota logo and integrated a neutral control light. The only visible deviation of the period-correct approach is the small digital KOSO OLED instrument, integrated into the upper triple clamp. It provides information about speed, distance, coolant temp, battery voltage, rpm, fuel level, oil tank level, ambient temp etc. and the control lights for indicators, high beam, fuel reserve and oil tank level. “Apparently Suzuki’s GT750 runs on a separate oil pump for engine lubrication depending on throttle position. The required external oil tank was integrated into my fuel tank by an internal divider in the rear section of the tank, with a filler neck under the seat. Speaking about the seat upholstery, I was not able to find anyone in Austria who could produce it to my requirements, luckily the guy from Serbia who produced the bodywork was able to connect me with an upholsterer in Hungary who did a perfect job for very reasonable money! “Finally, the paint job: I am definitely not an easy person to please when it comes to quality of painting. My eyes are very sensitive to anything that isn’t perfect, even a misplacement of a decal by one millmetre, I just catch it immediately. So it took me many years until I found a paintshop who I can fully trust. Franz Firlinger is a one-man show in a beautiful rural area close to the borders of the Czech Republic. Franz understands the special requirements for custom bikes or fully restored bikes compared to the relatively simple task of painting a car. He is a biker himself and as he’s painted 10 of my bikes I know he’s a perfectionist. So, Franz is responsible for the look of my Bimota: he painted the wheels, the frame and swingarm, the engine cases and the bodywork. Cheers Franz! “The frustrating thing is that I will never be able to do a real extended road test with my bike because of the one-off frame: there is no way I can get the bike street legal in Austria. It would be treated like a new bike which was never registered before, and it would need to meet actual emission and noise limits – you can imagine how impossible this would be once you see, smell and hear this Water Buffalo! My rides will be limited to parades on club events, maybe track days and on private roads. It does not matter too much, I enjoy it so much even if I only sit in front of it and watch it, with a pint of lager in my hands (here in Austria we would say “ein kruegel bier”). “I made my dream of an HB1 come true at a fraction of the price of the original bike. And don’t forget: compared to my unique replica bike with its large displacement two-stroke engine, an original Bimota HB1 is almost mainstream... and that’s not my thing!”
“I am definitely not an easy person to please when it comes to quality of painting. My eyes are very sensitive to anything that isn’t perfect, even a misplacement of a decal by one millimetre, I just catch it immediately. It had to be perfect...”