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Old 09-20-2009, 11:19 AM   #1
nlong001
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Default 97 CB750 Magna

I had done some modding on my honda magna and now it wont start. I had taken off the air intake manifold and am running straigh velocity stacks. To get a vacuum for the carburetors I drilled a hold in each intake port on the engine and set up a tube system to fill that need. Any ideas on why this would cause my bike not to start would be appreciated.
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Old 09-20-2009, 12:17 PM   #2
seruzawa
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Your bike won't start because you removed the airbox and you are using straight velocity stacks. Then you apparently decided to provide vacuum for the CV carbs by drilling holes in the intake ports? What possessed you to do this? The vacuum in the intake port (between cylinder and butterfly) is maximum with the throttle closed. It's the opposite of taking the vacuum off of the airbox.

These bikes are tuned to a fine degree to meet modern emissions standards which means they run very lean stock. If you surf various bike blogs you will see a stream of people who made their bikes run like shyt after their home mods. You really need to know what you are doing to get away with stuff like this. We get a fair population of people asking your sort of question after changing intake tracts.

Plug the holes in the manifolds and put the airbox back on. Even if you get the bike to start and run it's 99% certain that the hp and torque outputs will be worse than stock. Your pilot, needle and main jets will have to be experimented with by trial and error on a dyno for hours and hours to get it set up right.
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Last edited by seruzawa : 09-21-2009 at 09:32 AM.
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