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Help with new VM34 pair - KZ750 Twin 10 Aug 2019 15:41 #809009

  • fastfrank
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HI - I just installed (partially, haven't hooked up throttle cables yet) a new pair of VM34 carbs from MikuniOZ, which come pre-jetted for this bike.
I'm having a hard time getting it to run off of choke. It will start up on choke and idle, currently at about 2000 RPM but was 3000 previously. Problem is, with the bike warmed up and flipping the chokes off, it will die pretty quickly. I figured that it needed to run a richer mixture, so I moved the mixture screws in to 3/4 turn out, which should be way richer than the previous two turns out they came set with.

Should I set the idle speed even higher first, while on choke, and hope that it will run and settle into a lower idle? I'm not really experienced with tuning VM round slides, even though I had VM33s on my big zuki GS.

Need some advice here - thanks!

fastfrank (I’m a newbie here)
(rapidly aging and not so fast anymore)
78 KZ750 Twin
83 GS1100ES
99 ZRX1100
13 GW250

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Last edit: by fastfrank.

Help with new VM34 pair - KZ750 Twin 10 Aug 2019 16:07 #809010

  • Nessism
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The choke idle speed is typically independent of the normal idle speed. I'd set the base idle higher and then see what happens.

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Help with new VM34 pair - KZ750 Twin 10 Aug 2019 18:24 #809014

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OK - looks like I need to go up a size in pilot jets: I can finally get it to idle, without popping, at only 1/4 turn out on the mixture screws, and since CW is richer, I need a richer pilot jet. Not yet sure what MikuniOz put in there, but I'll find out shortly. I guess the common range for this carb is 20-25.
Of course, I'm tuning without air cleaners installed, so that would make me run it richer a bit, too.

Still have to figure out what all I need to take apart to get the stock airbox out - it is free in there, but blocked in by other parts.

fastfrank (I’m a newbie here)
(rapidly aging and not so fast anymore)
78 KZ750 Twin
83 GS1100ES
99 ZRX1100
13 GW250

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Help with new VM34 pair - KZ750 Twin 11 Aug 2019 02:02 #809023

  • DoctoRot
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I had to remove the rear wheel, fender and battery box to remove the air box from the rear

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Help with new VM34 pair - KZ750 Twin 11 Aug 2019 13:31 #809041

  • gd4now
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Unless you plan on running pod filters I would suggest you hook up the stock air box with filter before you attempt to do any tuning. With out any air filter, pods or stock, it will be running way lean as more air is entering the carbs than the stock jetting is expecting.
1977 KZ650 B1
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Help with new VM34 pair - KZ750 Twin 07 May 2021 11:43 #848170

  • mitchm114
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Did you ever get this resolved?

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