1997 BIMOTA BB 1 SUPERMONO BIPOSTO SPECS AND REVIEWS

The Bimota BB1 is only for collectors and enthusiasts. Positives include stunning appearance, outstanding handling, and Italian exclusivity. Unfortunately, for most individuals, the cons (lack of power and significant engine vibrations) outweigh the positives. Furthermore, the Bimota BB1 is not cheap, and dealer support is nearly non-existent.

Ride Quality / Brakes

This is where the Bimota BB1 Supermono really shines. Although the engine is unimpressive, you can make up ground on the brakes and in the turns. The custom aluminum frame, steep steering, and small (for the time) weight combine to create a very agile, sweet-handling motorbike. Brakes are good, but not outstanding by modern standards.

Engine

This is where the Bimota BB1 Supermono really shines. Although the engine is unimpressive, you can make up ground on the brakes and in the turns. The custom aluminum frame, steep steering, and small (for the time) weight combine to create a very agile, sweet-handling motorbike. Brakes are good, but not outstanding by modern standards. a The engine in the Bimota BB1 is the Rotax-developed 652cc single cylinder used in BMW’s F650 series. It’s torquey at low rpm and has a pleasant burble. But it won’t go that fast – get near to the 8000rpm red line and the vibration becomes unbearable. And it’s not particularly potent. Bimota claims 48bhp, which is roughly correct – but this is Yamaha XJ600S Diversion territory. Over 90 mph, it simply runs out of gas.

Reliability

Because there are so few examples of the Bimota BB1 in operation, and those that are don’t travel long distances, few difficulties have been documented. Engine reliability is good, and the motorcycles are made to a high standard rather than a low price. The main issue that owners have is the lack of a UK importer, which makes servicing and getting components difficult. However, this has been changed.

Instrumentation

The BB1, like most Bimotas, is a road racer, hence luxury was not a priority for the designer. An extra front brake disc cost £300. The fuel tank includes a convenient ‘glove box’ compartment. Bimota’s designers were sharp enough to keep the gasoline tank lower in the bike for improved weight distribution.

Oh, yes. One of those jobs where someone approaches me and says, “There’s a guy out front who wants you to heat up his…….”

I should preface this by saying that I was previously involved with a Bimota Supermono. It was one of the most unpleasant bikes I’ve ever ridden, owing primarily to the vibration. It simply didn’t feel right. I’d had to rebuild the engine and was now attempting to solve a problem caused by someone else’s misinformation, and I was hating every minute of it.

Anyway, after a while, I began to look forward to riding this little bike. The engine is from BMW’s Funduro, a fun little 650 single road/trail bike that we’ve sold quite a few of. Just a little sluggish. Any work more complicated than turning on the key, as with any Bimota, is a real pain, and involves dealing with the unavoidable consequences of a small manufacturer making something as small and light as possible.

Taking this expectation into consideration, I proceeded when it arrived. It’s a recent private import by a guy who moved from New Zealand to Australia, and it’s his plaything alongside his 916 SP. We found a local custom exhaust man (Neville at Moorabin Motorcycle Engineering) who removed the stock muffler and built a new dual muffler setup that included the rear bodywork mounting points. The owner picked up the bike from Neville, went to Dynobike for a dyno run, and then delivered it to me. As expected, he thought it was much better in terms of feel and response. It also made the typical “brap brap” noise of a loud single.

When I took it all apart, I discovered that getting to the carbs wasn’t all that difficult. Later, I discovered that I could reconnect the electrical components board and move it out of the way, allowing me to experiment with the carbs while the engine was running. I couldn’t get to anything worth adjusting, so I just got it running.

I noticed the bike wouldn’t idle after Antony had dropped it off. It was either throttle open and run or throttle closed and stop. When I checked the CO, I discovered that it was very lean at idle. Imagine my surprise when I discovered the jet kit included some larger pilot jets. I went for a ride after installing the pilots, needles and springs, and the smallest main jets. The mains weren’t bad enough to cause the engine to fail, but it did feel a little flatter than before the jet kit was installed. The needle setting was also satisfactory. The idle, on the other hand, was bizarre.

Returning to the workshop, I began experimenting. The first step was to get the idle going. To get a result, I had to wind the mixture screws out quite far. This was exacerbated by the fact that I had to remove the carbs and tip them up to change the screw setting. This rendered the usual mixture screw in-out impossible, necessitating extensive trial and error. I had something to drive with after a few different settings. The needle was dropped a notch to see what would happen. The mains were sized up by two sizes, and we were off again.

This was repeated until all of the needle notches were tried and one was chosen, the idle was tested in and out, and the mains for the dyno were determined. We were off to the dyno. Although it was a little more responsive on the lowest notch, I found that the needle setting I chose provided the best rideability. Compromise once more. I considered rubbing the needle down at the top, but decided against it for the sake of the greater good.

The dyno chart for the final setup (jet kit, open pipe) is shown in red below, the standard jetting and open pipe in blue, and the original in green. A significant improvement in the midrange, and a much nicer bike to ride around on. I was surprised at how enjoyable it was to ride in the end. Even with the open pipe, the cruise was quite quiet, smooth, and responsive.

Now it’s up to Antony to decide how far he wants to go. The torque curve below shows a steady fall beginning at 6,000 RPM. To achieve significant top-end gains, the torque curve shape must be altered. This is typically the most expensive part. Airbox modifications or removal may result in some overall curve lifting, but the top end will not be as easy or cheap to find. His original goal of 10 horsepower may be revised now that he has some response and rideability.

Oh, yes. One of those jobs where someone approaches me and says, “There’s a guy out front who wants you to heat up his…….”

I should preface this by saying that I was previously involved with a Bimota Supermono. It was one of the most unpleasant bikes I’ve ever ridden, owing primarily to the vibration. It simply didn’t feel right. I’d had to rebuild the engine and was now attempting to solve a problem caused by someone else’s misinformation, and I was hating every minute of it.

Anyway, after a while, I began to look forward to riding this little bike. The engine is from BMW’s Funduro, a fun little 650 single road/trail bike that we’ve sold quite a few of. Just a little sluggish. Any work more complicated than turning on the key, as with any Bimota, is a real pain, and involves dealing with the unavoidable consequences of a small manufacturer making something as small and light as possible.

Taking this expectation into consideration, I proceeded when it arrived. It’s a recent private import by a guy who moved from New Zealand to Australia, and it’s his plaything alongside his 916 SP. We found a local custom exhaust man (Neville at Moorabin Motorcycle Engineering) who removed the stock muffler and built a new dual muffler setup that included the rear bodywork mounting points. The owner picked up the bike from Neville, went to Dynobike for a dyno run, and then delivered it to me. As expected, he thought it was much better in terms of feel and response. It also made the typical “brap brap” noise of a loud single.

When I took it all apart, I discovered that getting to the carbs wasn’t all that difficult. Later, I discovered that I could reconnect the electrical components board and move it out of the way, allowing me to experiment with the carbs while the engine was running. I couldn’t get to anything worth adjusting, so I just got it running.

I noticed the bike wouldn’t idle after Antony had dropped it off. It was either throttle open and run or throttle closed and stop. When I checked the CO, I discovered that it was very lean at idle. Imagine my surprise when I discovered the jet kit included some larger pilot jets. I went for a ride after installing the pilots, needles and springs, and the smallest main jets. The mains weren’t bad enough to cause the engine to fail, but it did feel a little flatter than before the jet kit was installed. The needle setting was also satisfactory. The idle, on the other hand, was bizarre.

Returning to the workshop, I began experimenting. The first step was to get the idle going. To get a result, I had to wind the mixture screws out quite far. This was exacerbated by the fact that I had to remove the carbs and tip them up to change the screw setting. This rendered the usual mixture screw in-out impossible, necessitating extensive trial and error. I had something to drive with after a few different settings. The needle was dropped a notch to see what would happen. The mains were sized up by two sizes, and we were off again.

This was repeated until all of the needle notches were tried and one was chosen, the idle was tested in and out, and the mains for the dyno were determined. We were off to the dyno. Although it was a little more responsive on the lowest notch, I found that the needle setting I chose provided the best rideability. Compromise once more. I considered rubbing the needle down at the top, but decided against it for the sake of the greater good.

The dyno chart for the final setup (jet kit, open pipe) is shown in red below, the standard jetting and open pipe in blue, and the original in green. A significant improvement in the midrange, and a much nicer bike to ride around on. I was surprised at how enjoyable it was to ride in the end. Even with the open pipe, the cruise was quite quiet, smooth, and responsive.

DYNOBIKE (03) 9553 0018 provided the Dynochart.

Now it’s up to Antony to decide how far he wants to go. The torque curve below shows a steady fall beginning at 6,000 RPM. To achieve significant top-end gains, the torque curve shape must be altered. This is typically the most expensive part. Airbox modifications or removal may result in some overall curve lifting, but the top end will not be as easy or cheap to find. His original goal of 10 horsepower may be revised now that he has some response and rideability.

DYNOBIKE (03) 9553 0018 provided the Dynochart.

Update:

The original bike I was involved with, which Moto Italiano had imported for compliance back in ’96, had been sold a few times before ending up in the hands of a BEARS racer. He had significantly modified it, including having JE make him some high comp pistons. He had to order 4 for JE to do them from memory. Antony purchased one of these and had us install it. You can’t even get the head off with the engine in the chassis, so it’s an engine out job.

The piston had a high compression ratio. 14:1 was probably mentioned to me at some point. Antony had also discovered a German company called Team Pami, which has a long history of racing these bikes. They sell hot up and big bore kits in various stages, as well as head work and other accessories. Antony had purchased a pair of Mikuni 36mm flat slide carbs from them. The airbox was also removed from these carbs, which were equipped with two uneven length carbon fiber bell mouths. The jetting and bell mouths are based on what Team Pami discovered to be effective, so I was content to leave it at that.

So we installed the piston and carbs, got everything running, and Antony took it to the dyno for a test run. I haven’t ridden it or had the opportunity to assess the tuning because this bike is track only and I’ve never even seen it with its current revised fairing. But Antony thought it was fine because it didn’t ping.

Unfortunately, it returned a couple of track days later, having spat an oil hose off the dry sump tank and splattered oil all over the bike. This is not what you want when tracking. It was assumed I’d left a hose clamp undone, and I had no proof (as you don’t), so I wore it and we got it back up and running. The following track day, it did the same thing, but this time it also expanded the dry sump oil tank sufficiently to pop the battery out of its recess and deform the tank. We went looking because I assumed it had an engine pressurizing problem.

Antony also brought in one of the plugs it had been running to show me, which was grey and, in his opinion, running fine, despite the fact that it appeared to be covered in melted piston to me. The ground electrode had melted off one of the plugs we removed (the outer one), so I wasn’t surprised when the leak down test revealed a lot. After removing the engine and pulling the head, it was discovered that the piston had lost the top ring land on the inlet side, all the way down to the valve reliefs. There was no trace of the missing pistons, and only one spot of head damage, where the remaining end of the ring land on one side had lifted and struck it. Given the alleged compression, I wasn’t surprised that it had been run on 95 unleaded (our mid octane unleaded at the servo).

Antony purchased a replacement piston from Team Pami at a 12:1 ratio. This had a much smaller dome than the previously installed JE, which made me very happy. We also had to replace one inlet valve that had begun to recess noticeably. So we did all of that, put it back together, and went to the dyno to see what was up. At this point, Antony was understandably paranoid about the oil spewing out while riding, and I was becoming paranoid in general.

When Antony first purchased the Mikuni carbs from Team Pami, he also ordered a vacuum fuel pump, similar to the ones found on Ducati Monsters. I wasn’t sure how it would perform sucking fuel from the underslung tank, but Gottfried assured me that they’d never had any issues (while winning numerous Supermono championships), so I was satisfied. I’d added a one-way valve to the pickup in the tank to aid in priming the system, and there didn’t appear to be any issues the first time it was dyno’d with the carbs and piston installed.

We wanted to check the fuel pressure this time, so we attached a gauge to the carb inlet and went to the dyno. This caused a problem because the pump would only pump fuel if it had a closed circuit on the supply side, which I had when I first installed it. It wouldn’t pump fuel out of the tank if the fuel hose was disconnected at the carb. Hook up the hose, and it was soon happily supplying fuel. We dropped that idea because I figured the gauge was giving the pump enough open volume to effectively kill the vacuum it required. So it would slowly fill the float bowls and be fine for the first run, but the second run would suck the bowls dry halfway through and it would fall in a heap.

We tried opening the fuel cap to see if there was a problem there, but the problem persisted. So we tried an auxiliary fuel tank above the carbs, and it worked perfectly. We assumed we had a pump problem at this point, but given that it was fine initially – the bike had never had an obvious misfire causing fuel issues while melting the piston – it was all getting a little confusing.

To try to solve the problem, we installed an electric pump, this time from a carbed ZX9. A small pump that generated pressure and then shut down worked perfectly, giving us 1.5 psi at the carb from memory. The problem of running out of fuel on the dyno was solved, and we got a nice string of runs.

Another issue we’d noticed as soon as the JE high comp was installed was a lot of oil coming out of the engine breather. It began as a small tube on the front of the right hand (alternator) engine cover and pushed oil out almost as soon as the engine was started. We initially dealt with it with a catch bottle, but Antony had a very nice alloy breather tank/box made up that sat behind the carb inlets and also provided a back and floor of sorts to the area behind the carbs, essentially creating an airbox in conjunction with the tailpiece at the sides and electrics plate above.

We added another breather outlet to the center of the alternator cover, where there is a removable plug that allows you to turn the crank. This has an M18 x 1.5 threaded fitting with a possible internal hole of 12mm. We ran about a half-inch tubing from this to a junction block with the original breather outlet, then up to the breather tank behind the carbs.

This larger tubing has approximately twice the ID of the original, which means four times the internal area and is far less likely to be blocked by breathed oil, which is then pushed out by the air behind it. And, with the main outlet perhaps 10mm from the center of the spinning alternator, there would be a centrifuge windage effect inside the cover, assisting in keeping oil out. It certainly worked; there was no oil in the new (clear) tubing, even at the alternator cover outlet. When you consider that this engine changes its crankcase volume by 650cc every 180 degrees of rotation, you can see how important a good breather system is when it regularly revs to 8,000 RPM.

The graphs below demonstrate the progression from standard piston to both high compression pistons. From the original report, green is piped and jet kitted. The red piston is the JE very high comp piston, and the blue piston is the Team Pami 12:1 piston. As you can see, the piston, Mikuni flat slides, and lack of an airbox have increased the midrange while decreasing the top end. The 4,000 RPM dip is simply the Mikuni flat slides coming together after the throttle is pinned. Then comes torque.

If you read the last paragraph of the original report above, you’ll see that I thought the goal of an extra 10 Hp was unrealistic. The gain at this point is about 8, which surprised me. On the dyno, however, I noticed how the engine revved above 7,000 RPM. We were trying to keep the engine at 8,000 RPM as much as possible, but it would slow down from 6,500 to 7,300 RPM and then rev very quickly from 7,500 to 8,000. Looking at the above curve, you can see that power is still increasing at 8,000 RPM. It’s not much, but it’s still going up.

Based on this, I’d like to try advancing the inlet cams to maintain the 8,000 RPM red line. With the flat power curve above 7,500 RPM, I believe there would be more midrange available without affecting the maximum power output. Perhaps one day we’ll get to try it, hopefully without having to pull the engine out again.