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Discussion Starter #1 (Edited)
So I've seen Old School's Mikuni MV conversion. But I'm not completely satisfied with the idea. I think it is a Great idea. And I will be considering switching carbs maybe in a year?? I don't know.

Though I kinda like the idea of having a Constant Velocity type Carb (Like the ones most Hondas comes with.) Well I go back and forth on the idea. .. But I just don't like The carb model on the 450 lol... very lacking in the way of adjustments... I also think there are major problems with the diaphragms.. In testing the slide diaphragms, the they intermittently have a tendency to completely invert, which causes it to get stuck half way down in returning to idle.. inconsistently causing a lean mixture on one side or the other. The only reason the model has the slide diaphragm is to save physical space, in the vacuum chamber and cap.

Now, considering one can purchase a Mikuni carb based on specific measurements, Why not from Keihin? Keihin makes all the Honda Carbs, As well as many stock Harley carbs. Why not one of specific measurement? without the diaphragms?

So, at first I was considering the fact that the closest relative of the Rebel 450 (engine and carbs) is not the other rebels, .. or even the CM450... In Reality, The Rebel 450, was more like a Rebel frame on steroids, modified, basically to sport a CB Engine. Ever noticed how similar these engines Are/Were? The CB line of engines has remained similar for many years. Both Lines are Vertical/Parallel, Cylinders, many of the CBs had 4 Cyl, except for the smaller ones 250, 300, 350, 450 and 500. And the Carburetors continued to share a number of parts all the way into the 90's I believe.

Which brings me to the idea of Swapping the entire Carb, with the right size from a (newer?) CB. Though finding a new Twin Carb from a CB450 isn't possible either they discontinued production of the Twin Cyl CB450, in 87 I believe Also.


However, the CB line have an underground following all on their own... So much so that Keihin has been Reproducing the Race-Carbs for the CB line, with modifications. Apparently even making them safer for street use. (Removing the Tickler and adding a choke I presume.)

And.. doing some research on the idea, of course, I have not found a Darn thing about anyone else doing a similar swap. .. I mean a CB Carb in a Rebel?

But I have found a possible candidate, that shouldn't require much modification.

Twin Keihin CR31 special Round Slide.. .. >:)

It is a CV style Round slide, Side Draft carb, without diaphragms, apparently intended for side Draft (vertical) Twin Cylinder engines like the Honda CB350, of the years 1968-73. The same carb model is used 4up in CB900s. Which have very close to, the same volume per cyl as the Rebel 450. The model is also a popular as 1up for the Single cylinder Yamaha SR400s, which of course is Much larger. They are compatible with modern Triumph Twins as well.

So, I'm sure this would add a bit of performance to the big Rebel lol. The tune-ability alone!

.. .. ..
The conversion idea makes me giggle.

But, I'm not yet ready to attempt this (easy??) conversion.. So I'm just putting it out there.. .. (money is an issue)..

The biggest problem may be the intakes on the cylinders.. But it appears that the carbs are adjustable, in numerous aspects! Including how close to one another the carbs are. ... ..
Meaning, it might work keeping everything Else Stock!

The other problem, but I'm not completely sure, the CR specials might be just a bit too tall..
But I Think if the gas tank is raised just a bit, it would work.. The Top bar was given some extra room on the rebel450s Just to make room for the Throttle and Choke cables.
But with the Twin CR specials, The control cables connect on the right side, clearing up some room over the Carb caps... meaning the tank may need to be lifted Just for that.

Someone Please, Try This.
And let us know how it works out.
:grin2: ... OR.. Send me Some Dough, and I'll try it myself! LOL
 

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I too have looked at this problem and decided to go more modern and convert my 450 to fuel injection with a computer . Is not done yet as I am slowly designing and chasing the parts that I will need for the conversion. I think this is the best way to go and not with carbs
 

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Discussion Starter #3 (Edited)
You are converting the 450 to EFI??? WHOA!!!! .. .
Do you have a thread on this? What have you done so far?
I hope you start a thread.. .. Would love to see it!

Oh Dang, I intended to mention your Vacuum modification as well...
I tried my own version of it, but it didn't seem to help. Elenor seemed to run a little better strait stock...
and I removed it.

Hmm... .. I remember there being a Smartphone/Tablet-App made for engine stats (targeting Cars and trucks).
Speedo, Tachy, Oil Temp, Oil pressure, Coolant Temp, Trany Temp.. ... Tire Pressure lol.
Which makes me wonder if an App could be made to function As the computer.. .. ..


I feel like The Keihin CR31 Special would be a bit overkill. ... But I'm Sure it would run Excelently on these Carbs. .. . .. the CR specials seem like an upgrade for Any Side Draft engine across the board not just the old cafe racers.. If a used 90's 31mm Twin model could be found. .. I think it would save a lot of money. .. . But I have only found ONE! Listed at $350! New, Twin 31mm look to be selling at 6 to 8 hundred! .. And that just seems absurd to me!
 

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Don't have a thread started yet but will as things get moving a bit more than what I have done at the moment
 

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Hi There
actually I am heavily modifying my rebel 450 and one of the modification is carb and air filter.
For the first a friend borrow me 2 CR Keihin 30 for a fit check and they easily go without changing tank position. I have only to purchase the leverage for the throttle but it is a standard part.
For filters I plan to install 3 half cone with bended collector to bring them outside.
See the picture of the fit check
 

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Discussion Starter #6
WHOA!! AWESOME!!

I'm SO happy to see someone trying this!!
Do you have a thread? hope you start one!

The way you have it set up, it appears you don't have them on a rack. .. .. Do you plan on independent operation?
Do you have the bridging components removed? Or were they individual carbs?

It also looks like you got Strait on Intakes.

Something I'd Really like to see is some photographs. Side by side comparison of one of the CR's with one of the Rebel 450s.

Front, Back and sides.
I have my reasons .. LOL.. >:)
. .. . Personally I'd like to keep everything... else.. Well, "Nearly" Stock. ..

.. .. .. I KNEW I couldn't be the only crazy person wanting to put these monsters in a Rebel!
 

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I too have looked at this problem and decided to go more modern and convert my 450 to fuel injection with a computer . Is not done yet as I am slowly designing and chasing the parts that I will need for the conversion. I think this is the best way to go and not with carbs
Are you planning on using Microsquirt, or another standalone ECU?
I looked into switching the CBR to FI and am very familiar with Megasquirt as my ITB Neon runs it. It was just way too much money and time for maybe 5-7 more hp over the quad carbs.
 

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No am looking at using a Microtech computer that are made here in Australia
 
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