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Help with new VM34 pair - KZ750 Twin

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10 Aug 2019 15:41 - 10 Aug 2019 15:42 #809009 by fastfrank
Help with new VM34 pair - KZ750 Twin was created by fastfrank
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
Last edit: 10 Aug 2019 15:42 by fastfrank.

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  • Nessism
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10 Aug 2019 16:07 #809010 by Nessism
Replied by Nessism on topic Help with new VM34 pair - KZ750 Twin
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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10 Aug 2019 18:24 #809014 by fastfrank
Replied by fastfrank on topic Help with new VM34 pair - KZ750 Twin
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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  • DoctoRot
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  • Oh, the usual... I bowl, I drive around...
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11 Aug 2019 02:02 #809023 by DoctoRot
Replied by DoctoRot on topic Help with new VM34 pair - KZ750 Twin
I had to remove the rear wheel, fender and battery box to remove the air box from the rear

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  • gd4now
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  • Denco where did you go?
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11 Aug 2019 13:31 #809041 by gd4now
Replied by gd4now on topic Help with new VM34 pair - KZ750 Twin
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
Pods and Denco header


OLD KAW OWNERS SMILE ALOT

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07 May 2021 11:43 #848170 by mitchm114
Replied by mitchm114 on topic Help with new VM34 pair - KZ750 Twin
Did you ever get this resolved?

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