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The International CBX Owners Association • View topic - CBX Racing

CBX Racing

CBXs, new bikes, old bikes, cars, trucks, general chat, off topic, this is the place to post it.

Re: CBX Racing

Postby Syscrush » Thu Feb 06, 2020 9:59 am

Phil in Toronto
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Re: CBX Racing

Postby Warwick Biggs » Thu Feb 20, 2020 5:31 pm

You may not have noticed my temporary absence after I replaced my browser and then suffered the inevitable password problems, hopefully now remedied.

To respond to Phil's question about tuning the carbs - Seth says they set the slides by eye on the bench using the adjuster nuts in the pic. They are then basically tuned by changing the jets. Each cylinder apparently requires individual jetting so its a bit like a 2 stroke in this regard.

I have discovered yet another cause of my misfire. The bottom of the carb rubbers on 2 and 4 were split. This was not visible on the bike and only noticed with the head off in good light. Those cylinders would have been sucking more air than desirable.

I have also pulled the extended sump off to clean the pick up filter. It was not too bad and there were odd bits of neoprene, varnish and metal fragments but no evidence of the high temperature silicon gasket goo that I use. Earlier in this thread there was some debate about the pros and cons of silicon gasket goo and blocked filters but if you use modest amounts of high temperature goo it should not be a problem. I have used it to seal the cracks in my carb rubbers because a couple of new rubbers will cost around AUD$750. Ouch!

I'm making a few other mods to the motor while the head is off. When RPE did my cams Hugh was rather circumspect about the specs. Inspection reveals he took a short cut. Rather than build up the lobes to achieve more lift and duration he simply ground off the heel or baseline (the round base opposite the lobes) and then shimmed it up accordingly. Not the ideal way to achieve better gas flow altho' it works.

You can see from the pic below that the engine has been running too rich by the amount of carbon altho' it was quickly cleaned up with a nylon brush fitted to my rotary tool.
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Re: CBX Racing

Postby Warwick Biggs » Thu Feb 20, 2020 5:42 pm

To go back to the heavy carbs I have modified the linkage on my CR Specials to achieve an almost straight pull on the actuating cam. They are rather roughly assembled from Keihin USA and the angles and layout need a bit of adjustment by putting the actuating cam in a vice and bending it this way and that to achieve a perfectly straight pull.

This has made them a bit lighter at the bars altho' they are still heavier than is desirable. Here is a pic showing the mechanism. A larger diameter pulley would solve the problem.
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Re: CBX Racing

Postby Warwick Biggs » Thu Feb 20, 2020 5:51 pm

Jumping back to the pic of the head above you can also see that cylinder 4 has been sucking more air than the others.

Next, the valves will come out for inspection altho' they have passed the petrol pool test. If they are OK (they have occasionally kissed the piston crowns as a result of missed shifts) I will fit a new set of Kibblewhite springs, retainers and seals.
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Re: CBX Racing

Postby Syscrush » Fri Feb 21, 2020 9:11 am

Great update - that's really good news about finding the issue with the rubbers.

Could that stand-off for the throttle cables bend under the forces it sees in use? Would there be any value in bracing it to help keep everything nicely aligned?
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Re: CBX Racing

Postby Warwick Biggs » Sat Feb 22, 2020 7:53 pm

Quite possibly Phil. There is a lot of pressure on it. The other issue with the CR Specials and CBX packaging problems is that the carbs are almost down draft but the floats are designed to function on the level.

It has been suggested to me that making up a new manifold from alloy and then using ordinary freely available equal length rubbers would help both gas flow and level out the carbs. This would be a rather laborious mod, getting the angles right with a bit of tricky cutting and welding. It would also require re-designing the main jets/float bowls to make them shallower to keep the bottom of the carbs off the cases. As it is I have had to grind down the drain plug on one carb to stop it resting on the ridge in the cases that accommodates the primary drive chain.

Another possibility is fitting 6 Lectrons. Expensive but allowed under the rules. I would need to get one to see if they would fit better than the CR's. A third alternative is going back to my bored out CV's and removing the diaphragms. As I have pointed out in another thread, fitting CR Specials to CBX's is highly problematic.
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Re: CBX Racing

Postby Warwick Biggs » Sat Feb 22, 2020 8:06 pm

I'm racing in the Classic next w/e on the NC30 so, yesterday I took the 750 out to a practice day and I had some fun playing with some young guns on their 1000cc superbikes. I get a ridiculously juvenile kick out of cleaning up the kids and their reactions when I take off my helmet to reveal a visage old enough to be their grandfather.
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Re: CBX Racing

Postby Warwick Biggs » Sat Feb 29, 2020 6:21 pm

Just back from the track. This time with a sick NC30. It ran fine all through practice yesterday with a number of minor issues (including a grip that threatened to come off in my hand) fixed along the way.

Then in Q1 I was nearly taken out by somebody who threw their bike away right in front of me going in way too fast over the water tower. This was the exact same spot I crashed a few months ago and made me feel a bit nauseous. Then, a lap later my little jigger suddenly lost power. After pulling half the bike apart and doing basic diagnostics we were forced to retire what has been until now a very reliable bike. Suspicion is resting on the hard to diagnose spark unit that is apparently susceptible on the V4's.

Both my racers are now U/S and I''ve closed up the shed to focus on more productive endeavours for a while. Old bikes....!
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Re: CBX Racing

Postby Warwick Biggs » Sun Mar 08, 2020 2:36 am

Well, never overlook the obvious. Loss of power was caused by a power lead to the front coil coming loose. Once re-connected it ran fine except... Why is there always a qualification with race bikes? The radiator was almost dry. It was filled up and then lock wired b4 the race. Hmm, investigation with it running at normal temperature ruled out any obvious coolant leaks from either top or bottom radiator, the hoses or the motor. Plugs were all the right colour but a compression test showed it needed a de-coke and valve grind - all cylinders even at least at around 120 psi when they should be 160-213psi.

An air bubble into the catch tank every 10 seconds or so and the gradual discolouration of the pink coolant to oily brown suggested a more serious looming problem.

My diagnosis is a leaking head gasket, warped head or heads or cracks. Probably the former. Anyhow the heads will have to come off which is a problem because all my bench space is covered with CBX bits. I have another race coming up next month with the Easter Cup so will have to run the 750 Suzuki against the litre bikes where I'm sure to get lapped by the young guns. Maybe I should just concentrate on getting the CBX ready for the Seniors in May? Decisions, decisions.

Any other opinions on the coolant issue appreciated.
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Re: CBX Racing

Postby Warwick Biggs » Fri Mar 20, 2020 8:14 pm

Things are now moving so fast and the world has turned upside down since my last post. A difficult debate is now underway as to whether my club should continue with the Easter Cup races against the advice of government health experts who are trying to limit the spread of Covid 19.

Racers being the rugged individualists that they are (I'm being polite) tend to take a rather cavalier attitude to all things official. My view is that we will all have more time to fiddle with our bikes in the shed. Perhaps we could start a CBX Covid Projects page? Is it just me or do other people think of the words of Edgar Allen Poe's raven whenever the word covid crops up?
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