Carb swapping, immoral, deviant, or just plain wrong

[retrex]

The CBX doesn't really need all the carburetation unless the motor is a big bore and your going straight line racing.jeff

I recently read this article from mototune in which this guy talks about the intake ports on many bikes as being too large and that instead of opening up intake ports he reduces the size to speed up intake velocity. Claims it increase horsepower and makes the power more manageable. Does this sound plausible and do you think it might apply to the CBX? Could the intake ports of the CBX be to big for cylinder volume? Here is the site. Take a look and tell me what you think.



http://www.mototuneusa.com/think_fast.htm

[Jeff Bennetts]

Jeff -- Yeah. You're right. There are a couple of retailers who are presently putting together sets of CRFs for us, but they are really spendy. There are some other alternatives. The bad thing about the CBX though, if trying to fit carbs from other models, is the CBX's odd manifold spacing. It's really tight, much tighter than most other bikes. Takes some reworking to make it work. But it's doable. It appears that our comrades in Britain have been doing interesting things with ZX6 carbs, and I have researched another route that I hope to follow up on one day. Those your carbs? Man, they look nice. Thanks for the reply. :)

The carbs are off Paul Jasovskie's project bike, I had a hand in building them because I was also going to use a set on my project bike. After Paul installed them we found out how difficult they were to use on the street, they are for the higher rev ranges and are just too unpredictable for the street in my oppinion.



I have Pauls bike here at my shop and the first thing I did was remove them and rebuild them for resale, someone bought them off of ebay last year and I'm replacing them with a stock set that have been massaged a bit for the big bore kit thats in the bike. The bikes for sale and I think it will be a much better street bike without the flatsides on it.



jeff

[Jeff Bennetts]

The CBX doesn't really need all the carburetation unless the motor is a big bore and your going straight line racing.jeff

I recently read this article from mototune in which this guy talks about the intake ports on many bikes as being too large and that instead of opening up intake ports he reduces the size to speed up intake velocity. Claims it increase horsepower and makes the power more manageable. Does this sound plausible and do you think it might apply to the CBX? Could the intake ports of the CBX be to big for cylinder volume? Here is the site. Take a look and tell me what you think.



http://www.mototuneusa.com/think_fast.htm

No, not going to work on a CBX. The intake tracks on the CBX are not direct paths to the valves, only the middle two are. I have seen a CBX that had the intakes welded closed then rebored to make the paths straight to the valves and then a set of flatslides were added. A bunch of work, a bunch of money later and the setup only gained a few extra HP over mama Honda's original designed ports with the same flatslide setup.



If you have more money than midas put a fuel injected setup on the CBX, its programable and will better atomize the fuel flow to match whatever motor and type of riding your going to do.



Better yet wait for Mike Nixon to come up with the CRF carb rack or do it yourself and save some money over a EFI setup.



jeff

[Mike Nixon]

The CBX doesn't really need all the carburetation unless the motor is a big bore and your going straight line racing.jeff

I recently read this article from mototune in which this guy talks about the intake ports on many bikes as being too large and that instead of opening up intake ports he reduces the size to speed up intake velocity. Claims it increase horsepower and makes the power more manageable. Does this sound plausible and do you think it might apply to the CBX? Could the intake ports of the CBX be to big for cylinder volume? Here is the site. Take a look and tell me what you think.



http://www.mototuneusa.com/think_fast.htm

It's true. Not all that secret though. Yoshimura did this way back. Most everyone has done this, and it does work in many cases. I wrote some articles about this eight years ago. You can also find others talking about it if you look in the right places. Hennings, Hines, Axtel (Ron Dickey), etc.



http://www.motorcycleproject.com/motorc ... rting.html



http://www.motorcycleproject.com/motorc ... crets.html



Anyway, after reading my articles, you should see that there is a bit more to it than just using small ports. But McGivern is mostly right. :)

[Mike Nixon]

And ditto on the CBX's port problems. Kas Yoshima pointed out nearly 25 years ago that the CBX's outer four valves (two on the left, two on the right) don't even flow. They're stagnant. But there is a lot more to it than even that. The chamber is all wrong. The valves are oversized. The valve seats move around when hot. The stock carbs are poor performers (they flow less air than similarly sized carbs from the Yamaha triple, in part due to the choke plate). Ignition system is weak, and the timing curve wrong. And even in the best fiddle, few CBXs raise over 160 lbs compression. Like I say, a lot more to it.

[retrex]

Thanks Mike, lots of good stuff to think about in your info. No sense in going in a direction that won't get to where you want to go, or is not even there in the first place. Knowledge saves money and allocates it towards better projects.

[Mike Nixon]

Thanks for the comments. :)

[retrex]

I came across the following EFI gadget in a GS forum that I belong to. Thought I would throw it out there and see what others think. The cost does not seem prohibitive.



http://www.megasquirt.info/index.html

[Jeff Bennetts]

I came across the following EFI gadget in a GS forum that I belong to. Thought I would throw it out there and see what others think. The cost does not seem prohibitive.



http://www.megasquirt.info/index.html

Another good and real time source is Mark Sproul (ICOA member and sponsored racer) who works at a university, drag races CBX's and is having his collage team working on this project as we speak.



jeff

[IOWACBXER]

How about 6 AMAL MKII 34mm for deviant carb swapping?

http://www.interl.net/~jjanosik/images/79cbx.jpg

[Mike Nixon]

I came across the following EFI gadget in a GS forum that I belong to. Thought I would throw it out there and see what others think. The cost does not seem prohibitive.



http://www.megasquirt.info/index.html

The DOHC (900F/1100F) guys are all over this right now. Apparently it's getting to be a thing in certain circles.

[Mike Nixon]

How about 6 AMAL MKII 34mm for deviant carb swapping?

http://www.interl.net/~jjanosik/images/79cbx.jpg

Yup. That's deviant, John.