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Engine revs up high after cold start 31 Oct 2022 13:06 #876244

  • KZ650B_Joerg
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Hi,

quick question: Is it normal that my Z650B (VM24SS) at cold start with full choke revs up 1-2 seconds after start to over 3000 rpm? No trottle of course. Every time I need to reduce the choke quickly to keep the engine at a reasonable speed for warm up. It starts best with full choke when cold.
Apart of this everything is good with the engine. 

Cheers
Joerg

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Engine revs up high after cold start 31 Oct 2022 13:10 #876245

  • zed1015
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Yes! That's normal.
AIR CORRECTOR JETS FOR VM CARBS AND ETHANOL RESISTANT VITON CHOKE PLUNGER SEAL REPLACMENT FOR ALL CLASSIC AND MODERN MOTORCYCLE CARBURETTORS
kzrider.com/forum/23-for-sale/611992-air-corrector-jets-





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Engine revs up high after cold start 31 Oct 2022 17:29 #876252

  • Scirocco
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As zed1015 mentioned, it´s normal. KZ 650/900 VM carbs has not a choke but an extra fuel enrichment cricuit that by pass the normal idle adjustment. It´s like an extra little carb running more fuel and higher idle during the cold start period against the condensation losses of fuel on the cylinder walls.

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Engine revs up high after cold start 01 Nov 2022 00:27 #876257

  • KZ650B_Joerg
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Thanks zed1015 and scirocco! Yes, I saw the choke plunger during carb cleaning which bypasses idle mixture.
So I keep my left hand near the choke lever at cold start. 

Cheers
Joerg

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Engine revs up high after cold start 01 Nov 2022 00:49 #876258

  • zed1015
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Thanks zed1015 and scirocco! Yes, I saw the choke plunger during carb cleaning which bypasses idle mixture.
Cheers
Joerg
To be accurate the choke doesn't bypass the pilot circuit/idle mixure.
It just adds more fuel for cold starts.
The pilot circuit remains active at all times and adds to the entire fuel curve.
The overall jetting is a stack up of all the fuel circuits.
AIR CORRECTOR JETS FOR VM CARBS AND ETHANOL RESISTANT VITON CHOKE PLUNGER SEAL REPLACMENT FOR ALL CLASSIC AND MODERN MOTORCYCLE CARBURETTORS
kzrider.com/forum/23-for-sale/611992-air-corrector-jets-





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Engine revs up high after cold start 01 Nov 2022 02:12 #876259

  • willemZ900
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Have always  the same with my VM29 smooth, is normal behavior for VM carbs. 

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