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Helping me understanding carb tune basics - 2-1 Mikuni 21 May 2023 17:36 #885054

  • YamaKawa
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So I gave up the ghost on trying a fuel injection conversion on my KZ400. Wanting to stay away from the factory twin carb + air box for ease of meddling with the bike. I have a 2-1 intake and a Mikuni VM34. I know its a bit much for the bike according to most people, but it's what I got. I want to say my pilot is a 27.5 and either a 120 or a 140 for the main. I dont remember how its set up as the last I touched them were two years ago and I set up according to a person that lived at a similar altitude as me (~2300-2400 ft).

Well with whatever I got in in, I am get a nice steady idle @ ~ 1200 rpm (about right for the this bike, technically a little low iirc. Tons of power once you get in the RPM a little bit. I am having two main issues: hesitation when "blipping" the throttle (something I understand true slide carburetors dont like in general, but mine seems a little excessive) and a hanging RPM when coming off the throttle.

Bike is currently set up with Stock pipes with Sankei mufflers (appears to be OEM spec muffler?).

My understanding is that I need too go a step higher on my pilot (since tuning idle has my screw at ~1 turn out) and would the transition hesitation be a needle clip adjustment?

EDIT: it was a 27.5 pilot, but a 150 main. I found the 22 pilot that came with the carb, tried that and same result, so I am assuming lean and not overly rich. Cant seem to find the rest of my jets I had ordered so I will have to order them again.
1985 Yamaha XJ700N Maxim (airhead) - SOLD
1979 Kawasaki KZ400H (LTD), bought with 8416 original miles. - 'Tis my baby
1978 Honda GL1000 - SOLD
1995 Suzuki Katana - SOLD

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Last edit: by YamaKawa.

Helping me understanding carb tune basics - 2-1 Mikuni 05 Jun 2023 15:30 #885665

  • Cta2330
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Correct me if I’m wrong, but a common cause of lingering rpm’s is vacuum leaks allowing additional air to bypass the air filter. If there are any old rubbers on the carbs that would be something to check, and a easy way to check is to spray carb cleaner around carb connections and if there is a jump in rpm there is a leak. This is a common issue and test so there is plenty of stuff online to check with. This will probably not find small leaks though. Good luck!

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