The International CBX Owners Association

Hi
I have bought a Kerker 6 into 2 system, unused.
Can someone advise what jetting change (if any) is needed?
Many thanks
Kind Regards from New Zealand

Welcome to the site, Frank.
If you retain the stock airbox and filter the stock jetting should be fine.

Many thanks. Fast reply!

Welcome Frank, have you pulled an end cap and baffle to see if they have the street or race version baffles and what the baffle packing looks like?

Hi
I have not removed any caps, so I do not know whether road or race baffles.

nzfrank wrote:Hi
I have not removed any caps, so I do not know whether road or race baffles.

If they are unused the end caps should slide out easily with the baffle attached, long baffle is the street, the short is the race, so the race baffle will be much less restrictive and a whole lot louder! The street baffle would be best for a stock carb setup.

Here is some exhaust and carb 101 that any engine tuner worth his salt will tell you:
You need to consider what you are trying to do -
- have your motor run nice across the rpm band or
- deliver maximum performance
Why is there a difference? - let's look at that (at the risk that some wthout a degree may bark)
When a cylinder takes in air and gasoline and air/fuel mixture - in other words: jetting - is concerned, the exhaust valve is closed. The exhaust could probably care less what jetting is in the carbs.
Optimum jetting is a factor of air intake, i.e: airbox, intake tract. When this is tuned properly, the motor will idle fine and will - most likely - accept throttle in a smooth response over the rpm band.
A different exhaust will not change that.
When a cylinder discharges a burned load, the exhaust comes into play. The restriction in the exhaust will determine scavenging of spent gases and ability of the cylinder to reload.
If you want maximum performance at full throttle, you may not get this after you changed your exhaust and did nothing else.
A run on the dynamometer will tell you to rejet the carbs or do something else, less restrictive on the intake side.

There is a lot more detail to this, but it is a simple explanation why performance motors deliver peak at a certain rpm point or range and may be lousy when it comes to idle or roll on performance, for example.
I have used a variety of exhausts on my CBXes from stock to Suppertrapps (with different numbers of discs) to a 6-1 Schuele and a 6-6 Pipemaster and the jetting never had to be changed when rideability was desired and they never ran bad with stock jettings. They may not have made maximum power....then again, I never drag-raced any of them or operated them above 8000rpm for an extended period of time...
Food for thought.

Hi
Long baffle is street, short is race. Good. How long is long? Thanks

nzfrank wrote:Hi
Long baffle is street, short is race. Good. How long is long? Thanks

It's a bit longer than the can. So when you remove the can form the header, you'll see it sticking out as part of it goes into the collector


Sasha

I have the street baffles in my Kerkers. Standard jetting and standard airbox. Runs perfectly from idle to redline and at any throttle opening - sounds and looks good.

NZFrank - if you find an unused chrome set of Kerkers give me a shout.
I have been searching for chrome headers in very good condition for ages but they are rarely for sale.
If you don't clean where pipes join you get pitting and other corrosion and the PO neglected to do this.

There were three (3) different baffles available. As Jeff noted, they can be long or short, but also vary in diameter. The "Q", for quiet, baffle is the smallest diameter and the same length as the "street". Both the "Q" and "Street had a slight bend at the end where they slide into the lower part of the muffler body.

EDIT: THinking back, perhaps only the "Q" baffle had the kink that descended into the lower portion of the muffler. It may have had the same core diameter as the "street", just longer. It's been a lot of years since I had one in my grubby little paws........

NZFrank, I have my 79 in Auckland fitted with chrome Kerkers and havnt touched the jetting at all...its stock everything, except for the filter which is a K & N. Ive fitted 530 chain and sprockets and its transformed the bike - much funner [?] to ride with each gear stretched out about 3 mph is my guess and just makse the bike so much more relaxed at 120 kph...and each gear goes further without having to rev the nuts off it to get anywhere.
I also have a set of stainless Supertrapps Im shipping down with my kit '80 shortly and Im going to try the ST's on my bike before deciding whether to sell either the ST's or the chrome Kerkers.
Long story short Ive accumulated a 1980 motor [currently in my 79 in AKL - the 79 engine was blown up]] and all the bits to assemble a 1980 so when it hits NZ in August Im going to sell the kit including either the ST's or the Kerkers as part of the package. Ill then install the restored 79 motor Im sending with the kit into my 79 rolling chassis.
Al

If you've changed to 530 chain and sprockets, and notice 'stretched' gearing, then you didn't use the correct 18/42 sprocket combo. Sounds like you used a 40 tooth rear sprocket instead. 18/42 and 15/35 are exactly the same gearing.

Dave