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Author Topic: Carb retrofit onto CB450??  (Read 520 times)

Offline redrover

  • Posts: 192
Carb retrofit onto CB450??
« on: Jul 20, 2018, 14:39:58 »
Just got a rack of these Mikuni VM32 carbs (from a 83 GS750)

Does anyone know what it will take to take two of them and install into a 72 CB450?

Do I need a custom intake manifold? Special throttle cables?

Thank you in advance for any insights!

Offline davidricci

  • Posts: 78
Re: Carb retrofit onto CB450??
« Reply #1 on: Jul 20, 2018, 14:58:04 »
Someone wrote about 32 vs 30 for this bike on a thread favoring the 30ís. You should I think, determine first if the 32s are best before all that work. -D

Offline redrover

  • Posts: 192
Re: Carb retrofit onto CB450??
« Reply #2 on: Jul 20, 2018, 15:06:17 »
Ya good call! Iíve actually read up a ton on this upgrade and the consensus Iíve come across is that the 32ís are better for the 450 (while the 30ís are more ideal for the CB350).

Furthermore, all of the sites that sell the complete Mikuni kits for the 450, include the 32mm carbs.

This being a retrofit (not a kit), Iím concenered with making them actually fit and work.

Offline NoRiders

  • Posts: 680
Re: Carb retrofit onto CB450??
« Reply #3 on: Jul 20, 2018, 15:23:03 »
I'm no expert but they look like the carbs on my CBX550. They are individual carbs with fuel feed link and common throttle and choke mechanism.

From what I can make out, it'd be reasonably simple to remove the two outer carbs, therby retaining the centre mounted throttle linkage. Not to sure how the choke is arranged on your set but, the link bars holding them together should just cut down. The fuel is fed into each carb by a link pipe, again, by using the centre two it'd be a simple matter of blocking off the common fuel transfer outlets.

Offline redrover

  • Posts: 192
Re: Carb retrofit onto CB450??
« Reply #4 on: Jul 20, 2018, 16:20:07 »
Hmm ok so if I use the center two carbs, I wouldnít be able to use the other two on a different bike without some custom fabbing? Or another linkage?

Offline redrover

  • Posts: 192
Re: Carb retrofit onto CB450??
« Reply #5 on: Jul 20, 2018, 16:28:18 »
Also, why would I need the center throttle linkage if the 450 throttle cable spits off into two anyway? Couldnít I just attach each end of the cable to each carb? The carbs would be sitting a little bit further apart than on this rack anyway when attached to the 450, I presume?

Offline XS750AU

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Re: Carb retrofit onto CB450??
« Reply #6 on: Jul 20, 2018, 22:38:53 »
Quote
it'd be reasonably simple to remove the two outer carbs
I second this strategy - but the real issue is the pitch (distance) between carbs. It looks like the to center carbs are space wider than the outer to inner carb. Which spacing suits the engine intakes??
As for then having to make up a custom linkage for the remaining 2 carbs - you are going to have to do that anyway you proceed, as you only get one throttle linkage per bank of 4 carbies!!!!!!!
I think matching the pitch between carbies and intake is the most important issue. What have others done in the research you have done?
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Online irk miller

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Re: Carb retrofit onto CB450??
« Reply #7 on: Jul 21, 2018, 11:07:11 »
The butterflies and all mechanical mechanisms are connected on each outer to inner carb.  So, left side and right side are linked together.  Basically, the throttle linkage in the center works the inner carbs and transfers to the outer carbs through the rods.  IMO, there isn't enough to gain to go through all the work on this carb.  As far as slide carbs go, I think a Mikuni BST would be better, like what they run on the DR350SE or BMW F650.  The F650 is a pair, so you may get lucky on spacing, or be done at just having a custom intake made. 

Offline LiamG6

  • Posts: 17
Re: Carb retrofit onto CB450??
« Reply #8 on: Jul 21, 2018, 12:27:12 »
Those aren't VM32's?

Offline redrover

  • Posts: 192
Re: Carb retrofit onto CB450??
« Reply #9 on: Jul 21, 2018, 13:18:07 »
Well part of the reason I was excited about these Mikuniís was that I was hoping I could use two on my 450 rider, and the other two on the 500T brat Iím building. Doesnít sound like thatís realistic in terms of money/time/effort to make them work and perform well.

I found these from a 97 BMW F650... If the spacing is right, could I use the original 450 intake manifolds?