CBX Racing

[Warwick Biggs]

Back to an issue affecting the lump that any CBX owner considering fitting CR Special carbs should be aware of. Firstly, don't. Unless you are willing to spend a lot of time tuning the things.

Secondly, the CR slow jets that control the critical off idle and first quarter throttle response are particularly fine and quickly block up on conventional ULP due to modern fuel additives leaving a varnish as the fuel is used or evaporated. More additives such as fuel stabiliser will not cure this tendency. Unless you can source leaded avgas (illegal in many jurisdictions) you need to drain the float bowls after use to reduce the likelihood of the jets gumming up. This can be a messy and potentially dangerous process unless you are very careful.

That leads to the third problem. Whether you use a straight bank of CR's such as TIMS sells or a 'V' bank as sold by JB Power the number 4 carby drain screw will end up resting on the primary chain case bulge in the top of the cases. To avoid this problem I measured the thickness of the bottom of that drain screw with my micrometer and then ground off a few mm's so that it has enuf' clearance to undo sufficiently to drain that float bowl without pressing on the cases.

And that leads to the third problem. You need to paint or inscribe that drain screw so that it is identifiable at a glance so you don't do what I did last time and mix them up.

That resulted in a fourth problem. Trying to unscrew the un-modified drain screw on #4 carby in situ even with all the rubber clamps loosened resulted in cross threading the screw when I did it up again due to pressure against the cases. Being soft aluminium with a fine 1 mm pitch and 17 mm diameter you need a special and unusual die to fix it. Luckily for me a few hours careful work with a good quality thread file under a well lit magnifying glass had it cleaned up and back in service.

A number of people have experimented with mechanical fuel injection for CBX's and I would be very keen to hear if anybody has perfected such a system because I reckon this is probably the best method in the long run to improve CBX fueling and provide crisp linear power delivery. The modern PULP fuel problem in bikes built to run on leaded petrol is of course, widespread. Talk to any older model light aircraft owner.

[bobcat]

Are Mikuni RS flat slides legal there ?

[Warwick Biggs]

Not in Period 5 Bobcat. The fuel problem I discuss above I believe affects all older bikes running carbys altho the CR Specials are part
icularly susceptible. Do you think the Mikunis are any better?

[Warwick Biggs]

The only suggestion that I've heard for dealing with the gunge in modern fuel other than draining the carbs after use is to flood the fuel line with carb cleaner b4 starting. That from an ex Laverda tragic and Subaru mechanic so, just a suggestion

I have never tried it and suspect it could flood the plugs and make starting problematic. But it might be worth a try.

[bobcat]

Not in Period 5 Bobcat. The fuel problem I discuss above I believe affects all older bikes running carbys altho the CR Specials are part
icularly susceptible. Do you think the Mikunis are any better?

If the Mikunis aren't legal then the point would be moot but IMHO the Mikunis are
easier to tune and fitment might be better and they have an accelerator pump which
helps pulling away from turns.
As far as fuel goes I don't know but it would still be a good idea to drain them after
a race day.

[Warwick Biggs]

Or, I could cheat and use avgas. I have yet to see any fuel checks at the track and I'm told that it is a fairly common practice.

There is another rule that seems very contentious too. In Oz beta blockers are banned under our integrity in sport rules. Now I can't imagine that this common elder medication is performance enhancing (unless you consider keeping the competitor alive to be 'enhancing') and it would knock out a lot of older competitors. But then I haven't seen any drug testing at races either and so the rule is more honored in the breach.

When I was racing back in the early 70's most of the field would have been banned by today's standards. But then I reckon we had a very different approach to the sport than you see in youngsters these days.

[Rick Pope]

Is there some reason all the floats couldn't be tied together so that one, easily accessible drain could drain all 6 bowls? Or, just one drain on each side?

Or, put a fitting in the bowl with a short hose to a remote drain.

[Warwick Biggs]

Yes, in theory Rick. In practice finding a 17mm/1mm pitch aluminium O ring fitting with a hose connector that will clear the cases will be a challenge too far I suspect.

Here are a few pics from the w/e testing of the Super Duke. As you can see there is something of a style contrast with the rangy motard compared to a conventional track bike.

The biggest plus was great punch out of the corners from the 650 cc single. The handlebars are terrible. Too high and too wide and will either be replaced with flat bars or clip ons. At 100+ mph I was a giant wind sock. The front forks are way too long and squirelly under hard breaking and being tapered almost to the top are problematic. The Brembo brakes are good but not outstanding. I will try dropping the forks in the TC's. The existing clamps are KTM accessory items claimed to add trail and it was stable down the straight so perhaps pushing the forks up in the clamps will not hamper stability too much.

The banana seat is just weird and the plastic tank is too skinny to grip with the knees meaning it is not easy to steer with your legs. Ultimately, it is nowhere near as powerful, quick nor good a track bike as it's cousin, the 701 Svartpilen. The latter is a super mono whereas the Duke is a super motard. I was drifting both wheels towards the end of the session but not actually cutting better times. That is probably me as much as the bike as I tend to do the same times no matter what I ride but that is what I need to change. Just not sure this is the bike to do it on.

I will experiment with it but it is a poor cousin to the Husky and disappointing overall.

[Syscrush]

First, Braking CM55 pads are a cheap, easy, and worthy upgrade on this bike.

Second, the Duke is not a motard. It has a motard riding position, and motard-looking long forks, but the suspension travel and spring rates are much closer to an R6 than to a 690 SMC. Despite the banana seat, it's a knee-down bike, not a foot-out bike - as your photos show.

[Warwick Biggs]

Phil, I'm going to take issue with you on this. The guy who set this particular bike up is currently leading the Victorian super mono championship and a fastidious m/c mechanic. I don't know what he has done to the suspension but it is non standard. The TC's being an obvious example. He also has lots of experience with Brembos. I reckon a Brembo RCS master cylinder might improve feedback and it is something to discuss next time we meet. The pads are fine but the feel is not optimum.

I'm told you can get replacement fork cartridges that limit travel for road racing but not sure what is already in there. These are issues I will discuss with him in due course. The ride position is the biggest problem Phil. The shape of the seat has the rider sliding forward on the brakes and then sliding back on the throttle. I had to consciously haul myself forward on the bars to avoid missing shifts under power. Then the seat is so high that at over 6' in the old money I could still only get one foot down flat on the dummy grid. It gives a good towering view but puts the weight of the rider up too high. The consequence is that the slightest movement can unsettle the bike and combined with the too wide bars exaggerates the over sensitivity. Those slides I mentioned were inadvertent and caused by me trying to move my position to hang off and stand the bike up. The excess height is just like a lever. Compare my seat height to the other rider and you can see he has a much lower c of g.

Now I do have to keep stressing that I am over 70 years old and I don't have the flexibility of a youngster. I know how much that has changed because up to the age of 15 I studied ballet and had no trouble with the Russian sabre dance where you rest on your haunches, fold your arms and kick each leg out in sequence without losing your balance. These days I have difficulty getting out of a chair (altho' I find good champagne helps) and my lower back is in more or less constant pain. You can see from the above pic that my posture on this bike is exacerbating that problem.

Compare that to my posture on the Lump where my back is comfortably arched and I can easily lean into the corner. There you go, the CBX is a more comfortable track bike than a KTM Super Duke. Who would have thunk it?

The 701 is also far more track focused than the KTM and is my ultimate destination. They are chalk and cheese. Try one and see. The Duke is a stepping stone that I may be able to modify a bit but it is quite obvious that it has fundamental limitations compared to it's svartpilen cousin. That is my opinion at this point in time at any rate.

[Warwick Biggs]

Here is a better pic showing the contrast between the Super Duke and the Svartpilen. I won't say I'm a quicker rider than Dave on the 701 altho' I probably have more trophies than does he but we are at least on a par. He is a big bloke but had used the extra power of the 701 to blast past me on the straight half a lap before this pic was taken. Altho' I pulled a bit back under brakes he was still gapping me by more than a few tenths in all the corners and you can see why just by looking at our respective body positions.

There is absolutely no doubt in my mind that the Svartpilen is a far superior track bike than the Super Duke simply because of the more focused design differences even if the motors are similar. The KTM's super motard styling is an impediment irrespective of the high quality of the suspension and brakes. The 701 is just better in every respect as a road racer.

I also have no doubt that as the Duke currently stands (ie: as a production bike with modifications for the track), the Lump is also significantly faster bike even on a technical circuit like Mac Park. Of course, at a full high speed GP circuit like Phillip Island the CBX advantage would be even greater.

Nevertheless, I still think the KTM will be a better practice/track bike for me than the much faster GSXR for a number of reasons not least being much cheaper to run.

[Syscrush]

BTW - the 690 is not a Super Duke, it's just the Duke.

I appreciate the consequences of the riding position (which is basically the same as a supermoto) when it comes to riding dynamics. You're obviously 10x the track rider I'll ever be, and you know better than anyone what works well for you and what you're comfortable with.

The fact remains that the 690 Duke is not a supermoto. The 690 SMC is a supermoto.

[Warwick Biggs]

OK, super motard style then. KTM not only look weird they are weird. Why call your bike a Duke if it is not going to get confused with a Ducati and then call it a 690 when it is actually a 650. The '390' is also a 370 too so the Austrians seem a little confused or they are just perverse.

'Whatever the case, they also make the Svartpilen which is a much better base to start with and easier to convert to a competitive super mono. Fairly easy to get 76 rwhp without sacrificing that mid range grunt that makes these things jump out of the corners. And they look more like a normal bike. Not so weird after all.

[Warwick Biggs]

I have been discussing the possibilities of the 6 speed gear cluster for the Lump with Roly.

On paper it is appealing even tho' it is not a proper close ratio unit for racing. Nevertheless, it is still closer and should work better than the stock 5 speed box. Apart from the cost the main problem as I see it is that I do not know of anybody who has actually used it, much less raced it. Does anybody on the forum know who might have experience with it? Roly tells me it is produced in the UK so perhaps somebody in the now new kingdom might have some info?

[Warwick Biggs]

Back to our race calendar and I have entered the Lump in the Southern Classic at Broadford over 3-6 November. I have invited a contemporary and ex-factory racer Mark Lithgow to share the racing with me. He completely dominated the Seniors at the same track last w/e on his GPZ and has lost none of his top rider edge. However, he managed to bend a valve and they are not easy to find in his size so he will be available to help.

Mark has ridden the Lump b4 when we were partnered for an endurance race back in around 2017 and reckons he loves it. It is a more developed and competitive machine these days and it will be interesting to see what a top professional can do with it. He will also help me iron out a few handling issues in practice on the Friday so that should speed up the set up as I am a trial and error slow poke at getting the suspension working properly. With his experience he should be able to diagnose and sort it in a jiffy.

A few things to do b4 then including fitting the Barnett clutch and replacing all the fluids. In that regard I would like to try the new Castrol SRF racing brake fluid. At $130 a litre it is not cheap but it comes strongly recommended by one of our top ASBK team managers and anything that improves brake 'feel' is money well spent imo. Then I will take it out for a test in the weeks b4 the races and we should be ready. That is the plan at this stage and I just have to get back in the workshop and get on with it after a week camping out in the desert was brought to an abrupt halt by widespread flooding. All Oz major rivers are running 'bankers' after the 3rd La Nina year in succession.