News 2008

22nd. July

Yesterday morning Bryony and I popped over to Tim Blakemore Racing in Bristol with 'The Fang'. I didn't sleep to well the night before; a mixture of the excitement of that fantastic MotoGP race at Laguna Seca and the prospect of finally sorting out our bike.
Although Tim Blakemore specialises in dyno setup for modern road bikes, from Fireblade's to Vulcan cruisers, he does have the sensors for methanol and was happy to give 'The Fang' a blast.

After Tim securely strapped the bike down to the dyno we warmed her up while I checked for fuel leaks. At this point I was beginning to wish I had put my gas mask on, as the fans were blowing all the fumes my way. Tim then wound the bike up in 4th gear and at that point I had to leave the dyno room; my eyes were streaming and I was choking on what felt like neat methanol!
It sounded good, too loud even through my ear defenders. But when Tim shut her down, he explained that the bike was running incredibly weak and suggested fitting the largest jet I had for the next run. The dyno power graph was all over the place with a huge loss of horsepower in the space of a few hundred rpm, then picking up again before see-sawing up and down alarmingly; peaking at just under 50hp at 7000rpm.
The fueling graph was the most shocking: Fine up to about 6500rpm and then shooting off the scale for methanol in the wrong direction. Oh well it cleaned the plugs!!

With a 3.8mm (!) jet fitted we began attempt 2 but this time it was way too rich and unfortunately I couldn't stay any longer due to work commitments.

A big thank you to Tim and Wendy at Tim Blakemore Racing in Bristol for allowing us to run the bike (and filling Kingswood with methanol fumes!).
It was fascinating talking to them about the dyno, as they pointed out that besides sorting out your road bike for optimum power, the process usually results in better fuel economy under normal riding!
I should have done this years ago, it would have saved so much aggravation and wasted entry fees.
We are now on the lookout for an S&S Super B alcohol carb to replace the old SU. In the mean time check out Tim Blakemore running The Fang on the Dynojet dyno, turn up the volume too.

Lower curve is the fuel/air mixture, ideally this should be more or less horizontal. Note slight problem and correspondingly, shall we say, slightly erratic power delivery!

26th June

Updates every week; this is a novelty!
Whilst discussing various matters with one of my car racing customers I made a comment about weighing our bike, moments later I was heading home with two very accurate scales. Bearing in mind that the standard CB125TE weighs 114Kg dry, I was hoping to get under 100Kg. Was I pleasantly surprised or what: dry, the bike weighs in at a smidgen over 80Kg! That is less than a current 125 GP bike; if only I could find the extra 38bhp! Filled with enthusiasm Bryony and I heaved 'The Fang' onto the scales: 145Kg, the same as Valentino Rossi's 2008 M1 Yamaha! (Mental note: too many exclamation marks!)
So the next sensible thing would be to get 'The Fang' on the dyno, somehow I suspect Yamaha's claim of 200+ is a bit beyond our reach at the moment........

20th June

With the test booked for today and a busy week at work, things were a bit hectic again. However I made an interesting discovery: Due to the way the Hornet carb's are set up I used one outer and one inner from the set of 4. Now when I came to make some spare jets, I found that one carb had had a #88 main jet and the other #90. Of course I thought, the centre carb's run hotter and have bigger jets, so I fitted #90's to both carb's and made some #92's thinking they would be more than adequate: How wrong can you be!!

After warming the bike up, Tim tried to do a run on the dyno without success; way to weak was his verdict. Having asked what main jets I was using he handed me a pair of #122's. There then ensued 20 minutes of fumbling and swearing from Bryony, her Mum and I, during which the idiot who made high level exhausts was castigated for his foolishness at great length.

Finally it was done, time for run 2:

It was as if Tim had waved a magic wand over the bike; for a start it revved cleanly in neutral, which was a major step forward! A couple of blasts up to near 12,000rpm was proof of Tim's expertise: Nearly 60mph in 2nd gear and over 13 bhp at the rear wheel, despite thick clouds of blue smoke from the worn cylinder bores. The noise was utterly wonderful, or as a another customer said "that's a noisy little beast"!
A quick calculation suggests around 17+bhp at the crank, so an improvement on Honda's claimed output and much more to come when I have time.

Talk about money well spent! No more guesswork for me, one session on the Tim Blakemore Racing dyno and the carburetors and exhaust are sorted! I don't like to think how much expensive track time it would have taken to get anywhere near this. The dyno readout showed the engine is running a little rich up to 7000rpm, never mind Bryony won't be using such revs! Click on the link below to check out Tim's site:

Tim Blakemore Racing

17th June

Getting the bike started was the easy bit!
As the weekend drew nearer I began to realise how many little jobs were still outstanding. Worse still, due to the late appearance of the fork stanchions, our planned dyno test to set up the carb's was out of the question.
Still, the weather looked good, so off we went to Wroughton to the Vintage Club Sprint. Naturally Bryony was a little nervous shall we say, having only ridden the bike round the car park in 1st gear. All the fears vanished after the first run and from then on there was no stopping her, the biking bug has bitten!

Sadly the carburation was way out, with the engine bogging off the line and refusing to rev beyond about 6000rpm. During the lunch break I was pondering what might be done, when a comment from a fellow sprinter got me scouring the van for something suitable. Ha ha! a pair of fabric gloves, YES!
One over each carburetor mouth may have looked a bit bizarre, but seemed to help and allowed the engine to rev a bit cleaner.
Obviously it wasn't perfect but things got better, until a little later when a misfire set in. This turned out to be the brand new battery! Despite this there was no stopping Bryony and she was the last person to run at 5 o'clock and even managed a couple of wheelies. I can see that Bryony will be demanding something with a lot more power soon; what have I started!

So, next up is the delayed dyno session at Tim Blakemore Racing in Bristol. I'm interested to see how the Hornet CV carb's can be set up to run without an air box and with megaphone exhausts: Tim seems confident.

8th June

After a frantic effort by Bryony and I since Friday lunchtime, the bike is nearly finished. Read on:-

Numerous phone calls finally produced the wheel rims and spokes, though the fork stanchions proved a little more troublesome. By contrast Wemoto supplied the condenser the next day!
Finally I had everything together in one place, and Bryony having put up her end of year show, was available to supervise assembly.
In spare moments while waiting for all the parts to turn up, I made new stainless steel wheel spindles, spacers, washers and castellated nuts, along with dozens of other obscure fasteners in the same material.
Wheel hubs were blasted and polished, petrol tap bush on the tank welded up and replaced in the correct location (drat!). New clip-on handle bars and clamps carved from alloy billet.
I managed to shorten the alternator cover by 5mm and remove a couple of hundred grams more by turning down part of it, however the main benefit was narrowing the engine on the left hand side.

On an unseasonably sunny English summer day (!) I sprayed the tank and seat, put everything away and then remembered the front mudguard. Ah,...... that will be where the silver aerosol comes in handy then!
Bryony sourced the seat padding plus cover material and created the whole thing remarkably quickly, meanwhile the fork dust seals turned up and proved to be the wrong type. At that point I was still waiting for the stanchions, so it wasn't too difficult to pop the sliders in the lathe and modify them to suit the seals (even lost a few more grams!)

Frustrated by the non appearance of major parts I think I became a bit obsessed with detail; filing a stainless nut until it was just so, hours on the carburetor choke mechanism to keep weight to a minimum, adjustable lock stops and so on. Then I suddenly realised that the disc need drilling, more grams of swarf on the workshop floor!

Saturday saw us working on the wiring loom, and there was a bit of a panic when I realised we needed a ballast resistor to suit the 3 Ohm Dyna coils. Of course I had thrown out the one I had bought for 'The Fang', during one of my regular clearouts (when I throw away all the useful stuff and keep the rubbish). A quick trip to Merlin Motorsports at Castle Combe sorted that problem, shame it is enormous though.
We filled the tank with trepidation, amazingly no leaks! The endless minor jobs continued until around 4:45pm on Sunday when we finally wheeled the bike out of the garage for a test firing. With no kick start, the bike is started speedway style by pulling up the back wheel in 2nd gear.

YES! it goes! Even better it sounds utterly brilliant. Bryony tried a brief blip to about 5500rpm at which point it became distinctly LOUD, this is going to be awesome at 14000rpm! And in typical Honda fashion it is relatively turbine smooth.

Ok enough for now. We may be testing at Wroughton this weekend, so check back next week for more news; unless the British summer strikes again.

18th May

The last month has been very hectic, as the bike was stripped down for painting, wheel building etc. Parts are being moved to Bryony's bedroom as they are finished and hopefully this week the rims and spokes will turn up, along with the fork stanchions. The latter were too badly pitted to use, so a large section of the budget has gone into having them refurbished.
Faced with a delay of 2-3 weeks, I ordered a piece of aluminium billet and carved a new bottom yoke from it saving about 500 grams (am I sad or what?).
Meanwhile the top end of the engine was stripped and re-furbished along with a little head porting. Dumping the kick start mechanism lost another 1.2 Kilos, another 600 grams lost by shortening the alternator cover by 5mm and slimming the casting down. YES! Only 12.2 Kilos to go to meet my target!

Whilst I had the engine in bits I radiused the corners of the cylinder head and barrel fins to look more like the 60's works Honda racers. However the cam cover doesn't really fit in with the image I have in mind. So faced with something that looks as if it came of a 1930's Rudge Ulster! (and can't be changed), I thought I might as well make a feature of it. So out came the gold aerosol. This should work well with the red tank; we shall see.
Today I finally finished the carburetors. This has been a mammoth task, as adapting them to the wider cylinder spacing was a real pain in the neck and involved making a myriad of blanking plugs and extended connectors. Linking the two throttles alone was around 3 hours work.
Hopefully next weekend should see the bike on it's wheels, and my cunning plan for the battery carrier will be revealed. The end is in sight!

This really should be in 2007 but what the hell: Launch on our one and only run in 2007, with the clutch slipping really badly (as you will have heard if you watched the video). Encouraging to think the old thing can dig in and lift the front end a little with most of the power disappearing in the clutch. Photo courtesy of Juan Manzano of the VMCC sprint section.

29th March

A frantic 2 weeks has seen quite a bit of work done: Head stock shortened, footrest mounting tubes welded in, more frame mods, footrests and levers, gear and brake rods, rear brake back plate polished, engine de-greased, blasted clean and polished, heat shields for the exhausts, paddock stand made and so on. On the engine front I lost just under a kilogram by removing the alternator stator and cutting out the anti-ring links between the cylinder and head fins, the other 14 kilos could be more of a problem!

The clutch and brake levers have been blasted to bare metal and polished and a super quick action throttle is on it's way from The Netherlands. Sitting the battery was beginning to look a bit tricky, then I had a flash of inspiration, more next month.

10th March

In a busy week or so there has been some progress, primarily on the carburetors. About 10 hours went into carving new manifolds from billet and then adapting 2 of the Hornet carb's to the new cylinder spacing. Then I realised that the sheet steel spine of the Honda frame was in the way. No problem; out with the angle grinder and then a new tubular section was welded in place. Problem number 1: the stub on the petrol tank for the tap was in the way, aaaagh! Problem number 2: the top part of the Honda spine was still in the way! A few minutes with the grinder solved both of these for the time being.

Mounting for the rev counter styled after the 60's Honda GP racers, and as a finishing touch the red line is set at the 12 o'clock (ish) position.

Next up are the footrest mountings and more frame surgery, meanwhile I ponder how to loose about 15 kilos from the engine......

28th February

Two news items in one month shock horror!
Since reading an article in Performance Bikes magazine many years ago, I have always fancied having a go at hydro forming an exhaust, this project was the ideal candidate.

Basically you cut out the shape of the exhaust in 2D from 2 pieces of sheet, weld the edges together and then pump water between them to produce the 3D shape.
Having checked out the prices of high pressure hand pumps (more than the bike cost), I made one from stuff in the scrap bin, and used an 'O' ring from a CB500T gasket set for the piston seal.
The pump outlet was connected to the narrow end of the sheets and a bleed screw at the other end. Mindful of the risk of an unpleasant accident, I pumped it up in the vertical position to ensure all the air was excluded.

In the event this wouldn't have been a problem due to the myriad of pinholes in the first attempt! This first one also revealed that the profile is influenced by the profile as it takes shape, if you get my meaning. The second try was more or less spot on and by taking great care over the welds, not too many holes this time. I'm not saying it's perfect, but good enough for now, bearing in mind I want to finish the bike this year. All in all very satisfying and despite being made from only 0.8mm steel, they are very rigid due to the complex shape.

As you can see the tank and seat are nearly finished, so it will soon be time to pull it all to pieces for frame mods and engine rebuilding. The top yoke will be dropped by about 50mm and the fork stanchions shortened by about 70mm. Centre stand and brackets chopped off, and the centre section of the frame modified to clear the new carbs, footrest brackets added, wheels rebuilt with alloy rims...........etc

Eagle eyed readers may have noticed that I seem to have adopted a crude mono shock rear suspension, doubtless saving a couple of valuable kilos. Actually I took one unit off to see if it could be refurbished, this was a great success and will soon be joined by the other one, currently suffering from severe rust and peeling chrome plate.

11th February

Despite being incredibly busy during January I have managed to make some progress ; The seat is fabricated from 1mm steel sheet as the budget wouldn't extend to £50 for a fibre glass one, besides it was an interesting challenge. The hump is fabricated from lots of shaped strips welded together.

When it comes to the time to pull the bike to bits for painting, I will shorten the head tube so that the yokes don't stick up above the tank so much, this should improve the top line of the bike.

Thanks to the wonders of eBay I acquired a set of carbs off a Honda Hornet 4 cylinder 250. These are perfect for what I had in mind, allowing the induction tract a straight line to the inlet ports. Better still they are fitted with dinky little bell mouths, of course they will look a bit better when not balanced on a sponge.
Petrol tap is from a CB500T, surprise surprise! Oh and the Dyna coils are from The Fang pre twin plug days.

Finally a big thank you to Wendy at Tim Blakemore Racing for helping us out by providing a spare engine. In a couple of months I hope to have the bike ready for Tim's dyno to set the carbs up, meanwhile the exhaust is next up - more in March......

9th January

I don't think my daughter, Bryony, realised what the consequences of casually suggesting that she liked the idea of riding a bike again would have. Within hours madcap plans had been laid and the search began for a donor bike. Despite the fact that she learnt to ride on a Honda XBR500 single at the age of 15 we decided on a 125 Honda twin. One of the main reasons being that I am finding moving the CB500T based bike around a little difficult (it's my age you know), plus it would be nice to be able to pick up the engine easily!

The ideal bike turned up fairly locally in December so the Christmas holiday was time for fun with the angle grinder and welder. Luckily the bike is the CB125T model which was sold before learner laws curbed the power output from 16.5bhp to a measly 12.2. Better still these early models have wire spoked wheels and are 10Kg lighter than the 'Eurostyle' restricted version which was the basis for the bike my wife raced many moons ago. This bike managed a 16.7 ET, so with quite a few more horses and less weight the new bike should go well.

I've decided to go for an early 60's Honda GP bike look with a long slim tank, remember Luigi Taveri anyone?(really am showing my age now). The exhausts are a little special as you will see shortly. So far I've cut 3Kg of surplus steel from the frame and there is more to come. I may shorten the head tube, cut the fork tubes down a little and go down to 17" rims. Currently searching for a set of CBR250RR carbs, more soon.

The donor bike, mmm....

Better already, mmm........ !