CBX Racing

CBXs, new bikes, old bikes, cars, trucks, general chat, off topic, this is the place to post it.
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Warwick Biggs
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Re: CBX Racing

Post by Warwick Biggs »

By the way, a quick post script on my dragging brake problem. It was not bad enuf' to overheat the rotors so we carried on but a panel of experts conferred in my garage and concluded the problem was definitely in the calipers. Either it is crud build up or damaged rubbers as CBExtra posited as the cause. New stainless pistons, a bigger bore radial master cylinder and new seals are in the pipeline.

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Syscrush
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Re: CBX Racing

Post by Syscrush »

Another great report!

How was the cornering clearance on the X this weekend?

I'm very much looking forward to hearing how that new master works out for you. From a pure physics perspective, I don't get how the claims about them could be true, but so many people have responded so positively to them I'm sure that I'm missing something.
Phil in Toronto
A cool guy deserves a cool bike, a dork needs a cool bike...
Pics of Perry, my '79.

Warwick Biggs
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Re: CBX Racing

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Hi Phil, no problem with clearance but I was trying hard to hang off and stand the bike up.

I could not really relax and ride the Lump smoothly with much corner speed. It was more pick it up, point and squirt riding than racing. I need to tap the inlets on the motor side of the carbs so I can fit vacuum gauges to tune the low speed response off a closed throttle. The carbs are tuned for maximum power but need more work to make it useable power. Even the slightest throttle application off the bottom produces a violent surge that is hard to control when cranked over. It is also making gear changes ponderous and difficult - up or down.

The forum advice on radial brake mc's is unexpected so I guess I will just have to try it and see. Apart from ride days or away races I'm looking forward to a break from racing in order to work on these things. I'm also keen to reduce weight or at least move it around a bit. Mainly me. It always steers better and feels more stable when I'm virtually sitting on the tank.

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bobcat
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Re: CBX Racing

Post by bobcat »

I could not really relax and ride the Lump smoothly with much corner speed. It was more pick it up, point and squirt riding than racing. I need to tap the inlets on the motor side of the carbs so I can fit vacuum gauges to tune the low speed response off a closed throttle. The carbs are tuned for maximum power but need more work to make it useable power. Even the slightest throttle application off the bottom produces a violent surge that is hard to control when cranked over. It is also making gear changes ponderous and difficult - up or down.[/quote]

JMHO but I believe using a heavier crank, if not stock weight, would moderate the on/off, 2 stroke like
abruptness of the power and make it more rideable exiting corners. Restoring some flywheel effect will
also make shifting smoother. I doubt you would miss much straight away speed. I doubt that carb tuning
will yield what you are looking for. A less abrupt throttle pull (say half turn as opposed to quarter turn)
would also help. It sounds as though the motor makes plenty enough power to sacrifice a little to make
the bike rideable.
Bob
82 CBX, 81 CBX, CB1100F, 79/82 CB900F (avatar)

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Syscrush
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Re: CBX Racing

Post by Syscrush »

I'm sure you've thought about this, but maybe changing the cam on the throttle tube would help? These guys sell throttle systems with replaceable cams to help tune stuff like off-idle response:

https://www.g2ergo.com/product-category/street-bikes/

I have one of their throttles along with the "Jimmy Twister" outboard bearing and I like it a lot.
Phil in Toronto
A cool guy deserves a cool bike, a dork needs a cool bike...
Pics of Perry, my '79.

Warwick Biggs
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Re: CBX Racing

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I use a Venhill QA throttle with a choice of cams and yes, changing the cam may help. However, a crisp throttle off the bottom is what I really need. Tuning the NC30 with vacuum gauges markedly improved initial throttle response and I would expect the same improvement with the CBX. The crank is Honda Racing spec so I need to adapt and keep the revs in the power band. No going back.

I have bought a 16 mm Ducati S4 Brembo front brake master cylinder and will let you know how it works with the Prolink calipers once I have reconditioned them.

When I pulled the bike down for inspection after the races there was evidence of a fair bit of oil mist escaping from the catch bottle. The bottle itself contained nearly half a litre of oil. I am still using the stock breather hole and with the increased power there is obviously increased blow by and case pressure. So it looks like a second breather will be required to reduce pressure and contain oil loss. A threaded elbow with a hose barb will be fitted to the top of the blanking plate that covers the void where the alternator used to sit and a better vented catch bottle will be fitted.

Clearly I don't need to run a PCV for a race bike but the rules do require at least a 1 litre catch bottle. In the meantime I have made up a bottle within a bottle with a vent pipe to the tail to reduce pressure in the bottle itself.

I also plan to modify the seating position again. I have some solid shorter pegs coming and will further raise the seating position with more foam. Ideally I would like to move further forward but the tank restricts that so I'm also thinking of a shorter fuel tank with pingels on both sides. The existing LHS pingel is no good on tracks that run to the right because I have to carry excess fuel. I could plumb the rhs but a better designed alloy tank is the best solution. Maybe cut the bottom out and install a smaller alloy tank underneath but maintain the look? But that still restricts forward placement of the rider.

If anybody has any leads or ideas along these lines I'd be pleased to hear from you. So far all the fibreglass experts have declined my requests so aluminium would be my choice. Perhaps I could modify something off another bike with a central spine frame?

Warwick Biggs
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Re: CBX Racing

Post by Warwick Biggs »

A 900 SS Ducati tank apparently has a similar shape on the bottom. I know somebody with a 900SS mould but he reckons it's too much work.

Warwick Biggs
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Re: CBX Racing

Post by Warwick Biggs »

I have been talking to Rex Wolfenden about alloy tanks. Rex is half of the Melbourne based, brother partnership of TRex Racing which specialises in building CB1100R race replicas. His brother Clive does the frames and TIG work. Rex is around my vintage and was a long time Honda Oz race team mechanic. Their work is regularly seen on P5 grids around the country and features in earlier parts of this blog. If you have a lazy $100K lying around Rex might be convinced to build you one.

Rex currently has a CB1100R replica aluminium fuel tank for sale for AUD995.00. I know Roly used one on his Beast but with the necessary additional mods to fit my racer it is not an economic proposition and it is too large for my purposes anyway.

However, I have seen a CBX street bike wearing his highly polished alloy tank and it is stunning so for any ICOA members who are looking at dressing their machines up, Manx style, this may be an expense worth considering. If anybody is interested here is a link to the fuel tank listing:-
https://www.ebay.com.au/itm/125099611964
It will need a few minor mods but can be made to fit if you can afford it and it does polish up beautifully.

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