🔧 CISON V8 Carb Tuning Guide

Help and Guides
1

Been seeing a lot of people struggling with tuning this V8, so I figured I’d write up what’s been working for me.

Nothing fancy — just real trial-and-error stuff that should get you closer.

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:green_circle: If your engine CAN start

:backhand_index_pointing_right: Case A

Symptom:
Starts fine, but dies when you give it throttle, and idle is way too high

:backhand_index_pointing_right: This usually means your idle setup is off.

Here’s what I’d try:

  1. Bring the idle down first
    → Turn the low-speed needle OUT (counterclockwise) about 1/4 turn
    → Keep adjusting slowly until idle sits around ~2000 RPM

  2. If it still dies at full throttle
    → Start adjusting the high-speed needle
    → Turn it OUT (counterclockwise) 1/2 turn at a time
    → Test after each adjustment

:backhand_index_pointing_right: Case B

Symptom:
Idle is fine, doesn’t stall when revving, but won’t reach high RPM

:backhand_index_pointing_right: Usually not enough fuel in the high-speed range.

Try this:

  1. Turn the high-speed needle IN (clockwise) 1/2 turn
    → Keep testing until it starts pulling properly

  2. If idle changes after that
    → You’ll need to tweak the low-speed needle and throttle opening a bit
    → These settings affect each other more than you’d think

:backhand_index_pointing_right: Case C

Symptom:
Idle is fine, but it stalls as soon as you hit the throttle

:backhand_index_pointing_right: This is almost always a lean high-speed condition.

Fix:

  1. Turn the high-speed needle OUT (counterclockwise) 1/2 turn
    → Test and repeat until it can take full throttle

  2. Once it runs at full throttle
    → Hold it there and fine-tune
    → You’re looking for the highest, smoothest RPM

:red_circle: If your engine WON’T start

:backhand_index_pointing_right: Case A

Symptom:
No response when starting, but runs briefly if you block the intake

:backhand_index_pointing_right: Classic sign of not enough fuel at low speed.

Fix:

-> Turn the low-speed needle OUT (counterclockwise) about 0.3 turn
→ Keep adjusting until it starts without blocking the intake

:backhand_index_pointing_right: Case B

Symptom:
Only starts with choke wide open

:backhand_index_pointing_right: That usually means it’s too rich.

Fix:

-> Turn the low-speed needle IN (clockwise) about 1/2 turn
→ Adjust until it can start with the choke only slightly open (~1–2mm)

:gear: A few key things to understand

:wrench: What each adjustment actually does

  • High-speed needle → controls fuel at high RPM (brass side)

  • Low-speed needle → controls idle and low RPM (near throttle linkage)

  • Throttle screw → controls airflow (affects low-speed behavior)

:counterclockwise_arrows_button: Don’t mix up directions

  • Turn OUT (CCW) → more fuel (richer)

  • Turn IN (CW) → less fuel (leaner)

:bullseye: How much to adjust

Keep it small:

  • Low-speed: 1/4 turn (0.25–0.3)

  • High-speed: 1/2 turn

:backhand_index_pointing_right: Seriously — small changes make a big difference

:straight_ruler: Throttle gap reference

-> Around 1–2mm opening is a good baseline

:fire: One honest tip

There’s no “perfect setting” you can copy.

It changes depending on:

  • temperature

  • fuel

  • environment

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:backhand_index_pointing_right: So the real trick is:

:fire: Adjust a little → test → repeat

If you’re stuck, feel free to drop your setup (or a quick video) — happy to take a look :+1:

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