Author Topic: Mikuni Carb Balancing on CX 500  (Read 2707 times)

Glyn

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Mikuni Carb Balancing on CX 500
« on: January 23, 2009, 05:11:47 PM »
This is a little off (Vision) topic so hope someone can help.

As well as the Vision I have a Honda CX500 which I have put twin Mikuni round slides on.

The bike pulls nice and clean but seems a little rougher than standard, esp at tickover.
I've spent alot of time ensuring both carb slides are opening simulaneously and are at the same heights at rest.

As a result on the carb fuel inlets being higher than the CX tank outlet I have used an ZX fuel pump to feed the carbs. I have run this off the right hand side carb manifold, off the point where the carb balance tool is usually screwed in. I think this potentially could be the source of my problem, since the carbs now have different inlet air/fuel flow characteristics. Does this sound logical?

To fix this (and I would like to keep the XZ pump) I thought of running a similar length of tube from the other left carb manifold, so hopefully the airflow effect (like a YICS effect) would be balanced out. Or I could use a small electric petrol pump and remove the XZ pump completely. I'm not sure if a normal car fuel pump off E bay would pump too much fuel or not?

Any ideas welcome.  The XZ is having a bit of a break from the road while the CX gets a shakedown, but will be back in action soon.

Coil Coyle

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Re: Mikuni Carb Balancing on CX 500
« Reply #1 on: January 23, 2009, 07:31:15 PM »
Glyn,
       A "T" of the fuel pump outlet would give the same elevation change to each carb. If the XZ pumps too much pressure then a recirculation line with a small bleed orifice would solve that. The recircultion would need to be from an "X" fitting and place the orifice higher that the float bowl connection, run the bleed hose back into the line from the tank to the fuel pump inlet.
       The vacuum connection is just a power source, it is not regulating flow into the carbs.

In my opinion, :)
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Coil

jasonm.

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Re: Mikuni Carb Balancing on CX 500
« Reply #2 on: January 24, 2009, 01:32:33 PM »
Just get an electric fuel pump.  I got rid of the stock pump on my Vision. Using a Virago 535 electric pump. Electric Yamaha pumps  for carbed bikes of the 80's and 90's are all over Ebay.You just need one that has 1/4" pipes. Some are 5/16". As far as those carbs...What makes you think they will work properly? DO you have the proper jets for your engine?  You just can't strap carbs on and expect proper fuel air mixtures.  I do understand your use of non-Honda carbs. Some were junk back then.
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Glyn

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Re: Mikuni Carb Balancing on CX 500
« Reply #3 on: February 02, 2009, 05:59:39 AM »
I've done a fair bit of carb fiddling, with the Weber carb on my Vision. I started outwith the Mikuni's with the jet settings for a 650 XS Yam. A common mod is to put round slides on these bikes. I've changed the jets so the bike now pulls very cleanly, blowing no smoke. It runs great with them, it's just the roughness issue.

Update - I've taken the XZ pump off now and re sited the fuel pipe so the carbs are gravity fed, Blanked off the vacumn feed to the pump and manually reset the carbs.  Yet to take it for a decent ride. Hopefully the fall from the tank will be enough to run without a pump. Thanks for the advice. Yes the original carbs were rated as average, that's why I changed them.