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 »

But back to more prosaic matters. Where to start tuning the Lump. In the pic the tiny pilot jets at the top control the first third of the throttle movement. The main jets below cover the range from there to wide open. So we start with them.

Its currently too rich with 120's so we will try 118's first and then 115's. From there we want to have a crisp pick up so then we look at the super fine pilot jets.

But right now I have to go and load the CBX into the trailer. To be continued....
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Warwick Biggs
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Re: CBX Racing

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Everything started smoothly at the track. Both bikes were running OK & sailed thru' scrutineering. Once out on track things deteriorated quickly and I could only manage 2 laps on the CBX which would not pull the legs off a chocolate frog, to quote Barry Sheene. The plugs were all sooty so it was running too rich but they had a tan line and it was idling and running fine at low speed??? Go figure. OK put that back in the trailer and we took out the NC30.

Argh!!! Only running on 2 cylinders - it was a 15,000 rpm 200 - but this had happened b4. Sure enuf' a loose connector on a coil so after stripping the fairing off and re-connecting the errant connector we managed to get back out but my times were woeful. To top it off I was passed around the outside of the fastest corner on the track by a young woman on a 300! OK, she is an Oz Superbike top ten contender by the name of Tayla Relph and afterwards we had a long chat being situated next to each other in the pits. So good to see young women going well in the top echelons of the sport.

On the second day and after starting to come to grips with the little 400 (I'm over 6 feet in the old money and the 400 is tiny) I started to get down to business and soundly trounced a fast but septagenarian contemporary and then achieved a PB. That feels good! Quite a few serious incidents during the day were more sobering.

Back in the workshop I was reminded of that classic conflict between facts and beliefs. It seems to be playing out a bit in US politics at the moment. You see when I received the carbs I took off the float bowls and checked the main jets. They were 120's which is the standard Keihin fitting for 31 mm CR Specials. I had decided to put them on and see how they went as they came and so I assumed that the slow jets would be standard Keihin 65's and the needles on the standard position 4 of 7. That was my belief. Based on an assumption.

But my assumption was wrong. The slow jets were 62's meaning they were leaner than stock but the needles were on position 7, the bottom richest setting. Weird settings to be sure. Thus my belief that the bike was running too rich and my confusion over the sweet idling behaviour. I believed the needle was sitting lower than it was and could not understand the apparent contradiction in behaviour. My belief was at odds with the facts and had I checked properly to begin with I might have been able to adjust the needles at the track which can be done without removing the carbs. Oh well, lesson learned. Hopefully...

The leaner slow jet explained the good low speed behaviour and the higher needle meant it was way too rich on the throttle especially with a 120 main. The tan lines on the plug were where the idling on return started to burn off the unburnt soot from the fouled plugs. Now it all made sense.

Hopefully a smaller main jet and a medium needle setting will solve the problem. Hopefully....

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Re: CBX Racing

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One of the best things about the JB Power CR special carbs is that they are relatively easy to take off and put on. That is not something anybody could accuse the straight banks of and is a huge plus, if you've ever had to tackle the job.

So the 115's are now installed in place of the 120 main jets and I have adjusted all the needles to the middle position, 4 up from the lowest notch. That is easier said than done because the circlips are tiny and its an operation best done under a magnifying light. Even taking great care I had one shoot up into the ether. I heard it 'ping' off the iron roof and thought "bugger, I won't see that again" but was fortunate to find it on the floor 3 meters away.. They are so tiny I cannot hold them in my hand. I have to use a magnet to pick them up and my finest needle nosed pliers to set them correctly. Not an easy job in the pits, that's for sure.

So it runs fine in the workshop and as far as I can tell from the plugs its leaner but I need to test it under load. There are too many summer tourists around to think about a road test anywhere around here. Roly offered me a day on his dyno in Melbourne but last night the State Border slammed shut after a series of infections in hotel quarantine in Melbourne. The authorities are paranoid about the new variants altho' you would not know there was a pandemic on if you were watching the Oz tennis Open. Anyhow Melbourne is again classified as a 'hotspot' so I'm not sure I can take Roly up on his offer. Very irritating!

We used to have a good quarantine service in this country once until the economic rationalists rationalised it. Now we have 'hotel quarantine' run by State Governments who lack the Constitutional power to run it effectively. Now it's where you go to get infected. I see some big legal battles looming. But for the moment I'm stymied and can't really test the Lump.

So while I'm sitting around twiddling my thumbs I can write this and think of moving the electrics into the ducktail. I think I just need some 1.5 meter low impedance resistor HT spark plug leads and a few extensions of the wiring to the back of the coils is all.

AshishNJ
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Re: CBX Racing

Post by AshishNJ »

Good read. Thank you
1979 CBX (faster Red)
1981 CBX Streetfighter
2017 Aprilia Tuono.
Past rides : FZ1, BMWS100rr,S1000r,k1300S,YAMA RD350,Enfield 350

Warwick Biggs
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Re: CBX Racing

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Its the wee small hours of the morning as I write. I'm up early for the first day of practice at the track.

I did manage to get to Roly's and nearly 2 days of fiddling with the carbs. Its not perfect but hopefully good enuf'. We ended up with 100 main jets and 60 pilots. That is a big difference from where we started.

And I've lost 15hp from my previous set up. We think that is down to the 6 into 1 exhaust. The muffler on the Delkevic is fairly narrow and short and probably restrictive. Its still rather loud. Luckily the baffles are removable. Trouble is if I take them out I will probably get pinged under the noise regs because it will sound like all the banshees in hell wailing. Maybe even Odyseus's sirens. It will be very LOUD.

I may give it a go and see what happens. What do you think?

Amgcbx
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Re: CBX Racing

Post by Amgcbx »

Great read and always great information........
Give it a go..... open 6 into 1......thrilling sound
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Re: CBX Racing

Post by EMS »

40 years of fiddling with the exhausts have shown that a 6-1 in most cases is the worst option for a CBX. The only 6-1 that was worth installing and making more power than e.g.: a 6-2 tuned Supertrapp, was Schuele's exhaust from Germany. And if you look into this one and find out what it took to tune the headers you understand.

Amgcbx
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Re: CBX Racing

Post by Amgcbx »

I would not argue the fact that the Supertrapp pipe makes a bit more power, but this D@D pipe did ok for itself along with the motor/carb combo.... I can't remember a lot of the specifics of what went into my motor. I was a young gun then, 18-19 years young ,in 79 80. Connecting rods,pistons,cams carbs coils,etc and the bike kicked some butt around these parts back then.
All a distant memory.... bike has sat way to long. I'm not proud of that but had no choice. Some serious street racing and highway running remain clear though! The motor much preferred a Fall cool/crisp night more so than a hot summer day!
I've recently been riding a newer 2018 Yamaha MT09. A triple cylinder 847cc animal. A hoot to ride but needs some suspension help ...nothing Ohlins can't fix...miss the X though... big time.... I really need to throw some $$$$$ at her!!!!

Warwick Biggs
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Re: CBX Racing

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Just back from the track with mixed results. The Lump is running but there were a few teething problems.

The most serious was the throttle sticking open at the end of the straight due to the venturi affect overwhelming the Keihin springs. Not an unusual problem really and easily ridden around using the push cable but not something you want to have to focus on in a race - the need to physically close the throttle when braking. Relatively easy to fix tho'. Luckily I had an outfit crew with a Triumph rig nearby and they had a jar full of springs. A bit of lockwire and a nice long spring rectified thet problem.

The most annoying (apart from the rider jumping from diminutive NC30 to the Lump) in successive sessions - sometimes you can be unlucky when they jam up the classes. The old problem of a flat spot off a closed throttle. We saw this on the dyno and managed to get it down to about 3,500 rpm but its still not ideal and needs more tuning. Anyhow I can't fix that one at the track and will just have to try and keep the revs up above that spot.

I did take the baffles out (you can see it sitting on the table in the attached pic plus the effect at idle on my partner Fran) and it flew down the straight once it could catch it's breath and clear it's throat.

Tomorrow morning is qualifying but as it stands, I will just motor round at the back of the grid and try not to get lapped. I'm much faster on the NC30 even tho' I find it very cramped.
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Warwick Biggs
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Re: CBX Racing

Post by Warwick Biggs »

EMS Roly reckons there is a guy in Melbourne at Megacycle who made up a 6 into 2 into 1 exhaust that found an extra 30 hp for his salt racer.

Removing the baffle you can see in the attached pic definitely felt better by seat of the pants down the straight. Mac Park is not the ideal circuit for the Lump because it has some very tight and technical corners (its modelled on Cadwell Park in the UK). Phillip Island is much more suited to the big 6 or vice versa because its a high speed flowing track.
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Amgcbx
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Re: CBX Racing

Post by Amgcbx »

Quite simply Mr Biggs,,,, one thing I remember was the bike never carbureted as crisp and clean as the stock carbs.
But man, from anything past idle she pulled hard......also remembering similar wide open return issues where the 29's would get hung up ......

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Re: CBX Racing

Post by jt »

Amgcbx wrote:
Thu Feb 25, 2021 4:19 pm
Great read and always great information........
Give it a go..... open 6 into 1......thrilling sound
I love this pipe, Dave Rash (D&D Exhausts) had one on a CBX at the Nascar track Texas World Speedway in early 1980. Open megaphone like the one in the pic, the sound that it made at redline on the big Nascar banking and down the straights was remarkable to put it mildly! I distinctly remember the hair standing up on the back of my neck.

I have one but with the baffle, wish I could find one these ends to use with my headpipe. So if anyone has one I would be interested.
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Warwick Biggs
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Re: CBX Racing

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A better pic and times today but still at the back of the pack. This is a 125 track or at least a track where an RS 250 will out point a superbike. Not ideal for the lump but nevertheless we are slower than when we were on 18's 5 years ago. Age?

Looks like I will have to raise it some more as the Delkevic is now scraping in a new spot. Just touching the crank ends too so more height is required and the longer dogbone will have to be employed. Another day of racing to go. At least I picked up a second in P6 500 on the NC30 and 4th outright in a mixed field, albeit with a lousy time!
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Warwick Biggs
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Re: CBX Racing

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Thanks to Roly's efforts on the dyno we managed to complete the w/e program without too many dramas after a couple of years on the bench and the Lump came home ready to run again. No way was it remotely competitive against the Birrell Katanas, Harris Kwackas or TRex's tho'. They have motors with 50-100% more power and lives that can be measured in hours - if that. And $$$.

However, I still need to change a lot to get it percolating properly. And trying to race 2 very different bikes back to back is a no no, never to be repeated at my less than tender age. Compared to the 400 my style on the Lump had to be so much more aggressive, almost brutal, wrestling it around MP. My best time on the 6 was a 1'35 and I was near the back. When I had it on 18's 5 years ago I was consistently at least 3 seconds faster. On the 400 I was somewhat quicker and managed a fourth outright and a second in P6 500 altho' I was still 5 seconds off my best, probably because of having to readjust after hopping off the Lump and sheer exhaustion.

The 6 is noticeably less powerful than in the past. It used to want to wheel stand on the change into second gear but now it feels a bit lethargic. Looks like the 6 into 1 was a big mistake. I found keeping it above the flat spot in T1 and T4 a conscious effort too but it entertained the crowd and absolutely howled down the straight with the baffles out. Provided I kept it above the flat spot it revved out cleanly to the rev limiter. The auxiliary spring worked well to overcome the venturi effect and only marginally added to throttle weight but I need to devise a more permanent connection to replace the Heath Robinson lock wire.

The 2 main issues I need to work on (apart from rider fitness) are refining the tuning of the carbs and jacking it up a bit more. Even with the exhaust lifted up to the max and hanging off like a monkey I was still scraping at the end of the collector. Thankfully, I didn't touch the crank ends tho' which almost guarantees a highside. I was riding judiciously despite the race pressure as a direct consequence of the painful memories of past high sides caused by leaning on the crank cases too hard. Ground clearance remains the biggest impediment to corner speed and better lap times. The steering is still too heavy and was only marginally improved by dropping the front forks a few mms in the pits. Back in the workshop I will pull the rear shock off again and try the longer dogbone to lift up the back higher which should also sharpen the steering.

As for the carbs, the first step is another exhaust and then more tuning. I have Roly's contact for a specialist in Melbourne based upon his salt bike experiments.

Next outing for the Lump will be the seniors in May so I will need to get my skates on. Sorry about the pun Roly, it just popped out! Here are some watermarked pics courtesy of Pierre Caz. I will have to pay him once I decide on which ones I want. He is a CBX enthusiast and he took a lot!
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Warwick Biggs
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Re: CBX Racing

Post by Warwick Biggs »

And another...
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