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Discussion Starter #1
Hi Guys,
I have an old Honda CB400n that I want to turn into a caferacer.
One problem is related to the tank, that is not actually following the "pure rules" of the cafe racer design: the lower part ist not straight , so I'm convincing myself to replace it.
Any suggestion from your side?
Maybe someone of you already customized this model.
Thank youuu
Alfo


2018-07-04_17h09_16.jpg
 

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Alfo, there are few rules for cafe bike design.

The only rules I know are:
1: Make it run well and safely
2: make it perform as well as or better than stock
3: the only rule about "looks " is that if it's made right it will look right.

Have fun with it.
 

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welcome !
i would suggest fabricating some side panels that blend with the tank and also hide all that stuff that can be seen now
what you read about a certain line of form and what you see in images of cafe racers are all frauds they are actually going in the opposite direction of what a cafe racer was
believe me back in the day they were not modifying bikes to look and perform badly ,handle terribly spooky and be extremely uncomfortable even on short rides
but the builds and images on the internet that we see are overwhemingly terrible
although the original cafe racers emulating racebikes vwere not very comfortable
today's cafe racer is a completely fraudulent concept for a motorcycle if there is any idea of actuallky riding one
you could rise above !!use your own creativity and focus on making the bike better, beter to ride quick around curves the number one goal
the problem with your bike is it will never look like anything special unless you stop trying to copy the copycats who know nothing about the basic functional concept of motorbikes
the freame is shaped wrong to emulate a concept of a straight line from tank underside oin back past the seat
on another note
how does it run / did you ever have the stock airbox ? those carbs are notorious for being impossible to tune once you toss the airbox in the garbage
 

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Discussion Starter #5
Thanks guys for the hints... really appreciated, I think I'll follow your suggestions not changing the tank. I just have to be careful to choose a single-seat that fits well the line of the bike.

on another note
how does it run / did you ever have the stock airbox ? those carbs are notorious for being impossible to tune once you toss the airbox in the garbage
Actually it is not bad, just some power loss with the eingine just started, but when it is well warmed up it works smoothly.
 

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Hello guys...I need your help..I have the same bike which I would like to transfer in cafe racer....for now I replaced old with new exhuast and add sport pods....now I have a problem with carburator...I need to put bigger jets....stock are Kihin main 78 and small 108...what do you prefer to put in?
Thank you
 

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Hello guys...I need your help..I have the same bike which I would like to transfer in cafe racer....for now I replaced old with new exhuast and add sport pods....now I have a problem with carburator...I need to put bigger jets....stock are Kihin main 78 and small 108...what do you prefer to put in?
Thank you
I would install non vacuum controlled carburetors and then tune it about twice as easy, but that's just me, I like easy to work on stuff that works good. What you are trying to do there is make the most fuel efficient carburetor that existed a long long time ago, burn tons more fuel then it was ever designed to operate on.
 

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Thank you for your post...can you please send me a link which vacuum controller carburator is correct for Honda cb400n.....
Thank you very much for your help
 

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Thank you for your post...can you please send me a link which vacuum controller carburator is correct for Honda cb400n.....
Thank you very much for your help
The one that came on it is correct for the exhaust and intake that came on it.

Any vacuum controlled carburetor is really not suitable if you have altered the intake and exhaust to make it more free breathing.
i.e.. pods + open exhaust + CV carburetors = most difficult carburetor in the world to make work.

If your carburetors were of a variety that does not operate on the principal of a vacuum operating a slide valve you would not be having anywhere near as much difficulty making it work reasonably well.

To what extent have you modified the intake and exhaust?
 

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How restrictive are the exhausts compared to original?
You have completely shortened the intake manifold by putting the filters directly on the 2 separate carbs. The vacuum control for the carbs, does it come off one side of the manifold or both? Your carb slides are probably bobbing all over the place, if it was anything other then a vacuum operated carburetor, your twist throttle would be directly in control of the carb slide :| that's the basic difference in carburetor types. The ones you have were designed to save fuel.
 

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Can you put some link about velocity stack...this is my first bike and I dont know what is velocity stack...what I know that this pods looks good and hope to fix this issue some how othervise I will put stock air box back....but first I want to try new jets....hope I will not destroy the engine....
Please check picture above from Alfo he has the same pods...and looks like it works....
 

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If you want a bike that works good copy the ones that win races not the stationary ones that still have brand new tires with the little hairs on the tread.
You won't destroy the engine just as long as you keep good oil in it, keep the intake free of dirt and don't throw a valve chain or something crazy like that.
Is a Honda engine they take a pretty severe beating.

The concept of the velocity stack is to provide a more smooth flow of air into the carburetor, they don't like a lot of turbulence. Look at the rubber boot that originally went from your carburetor to the airbox where it was previously drawing from a large volume of relatively still air :| well actually the air is going slow and fast and slow and fast a whole bunch of times per second but that is the basic concept in practice.

The vacuum operating your CV type carburetors, that air vacuum pressure is also fluctuating all over the place every time your intake valve opens.

In a perfect world there would be nice linear air flowing through the entire engine, fuel (in this case gasoline) will be vaporized nice and evenly into that flow of air and achieve close to what is called the stoichiometric fuel/air mixture. This is ~14.7:1 for gasoline, 14.7 parts air to 1 part fuel. In reality most engines run a bit richer most of the time. An engine runs especially rich when accelerating, when it's cold, or under heavy load. Your engine needs to be operating close to that stoichiometric ratio at all times or performance and fuel efficiency will degrade. ... but your engine won't blow up or anything, that fuel/air ratio is just the point where 100% of the fuel will theoretically combust (that's a good thing)
 
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