logo elektroda
logo elektroda
X
logo elektroda
Advanced Search
logo elektroda
3D printer for home or business?
3D printer for home or business? Here are the perfect 3D printers to start with »
ADVERTISEMENT
Dostępna jest polska wersja

Czy wolisz polską wersję strony elektroda?

Nie, dziękuję Przekieruj mnie tam

The rotation of the 4t scooter is slowly coming down from the rotation.

Tom2602 19626 16
Best answers

Why does my 4-stroke scooter stay at 4–4.5k RPM for about a minute after I release the throttle before it finally drops to idle?

This behavior is most likely caused by false air entering the intake/carburetor, so check the intake stub, vacuum hoses, and the O-rings between the intake manifold and cylinder head/carburetor, and replace any cracked parts [#17022173] [#17028612] If the intake side is tight, inspect the carburetor diaphragm and make sure the choke/enricher works properly [#17040745] [#17040890] Also verify valve clearance, because incorrect valve lash can cause poor idle return on a 4T scooter [#17036184] The throttle cable itself is less likely if the throttle closes immediately and the problem remains [#17023662] [#17028437]
Generated by the language model.
ADVERTISEMENT
Treść została przetłumaczona polish » english Zobacz oryginalną wersję tematu
Report a violation of the law
Reply | New topic
  • #1 17022131
    Tom2602
    Level 3  
    Hello.
    I have a problem with the 4t scooter.
    It goes well into revolutions, but worse with descending from revolutions.
    More precisely, when I give the gas, it will normally go into revolutions and when the gas is released, it goes down to 4-4.5 thousand and keeps it for about a minute and then goes down to 2 thousand and it walks normally ...
    The symptoms are as if something is clipping ...
    Immediately I say that the line does not jam ...
    What could it be?
  • ADVERTISEMENT
  • #2 17022173
    1133
    Level 14  
    Hello
    Usually, the problem is with the left-hand air that gets on the carburetor connection.
    check the vacuum hoses that are connected to the stub and the stub itself is not damaged.
  • #3 17023662
    Staszek49
    Level 35  
    Check the condition of the throttle cable, it may be improperly laid or worn. Raise the seat and observe that the throttle responds to the throttle trigger and at what rate it returns to its original position.
  • #4 17028437
    Tom2602
    Level 3  
    The line works perfectly. The throttle immediately returns to the closed position and the scooter still keeps high speed ...
  • ADVERTISEMENT
  • #5 17028612
    barton21
    Level 26  
    There is an ebonite washer with an O-ring between the suction socket and the head, and the O-ring is also in the socket. Replace both O-rings. As it will continue unchanged, cleaning the carburetor and adjustment
  • #6 17030329
    Tom2602
    Level 3  
    Carburetor cleaned, washer between the connector and the head also a new O-ring, the connector is all new because it was cracked a little and the symptoms are still the same.
    I would like to add that the regulation does not give anything and to have slow speed, the rotation screw must be screwed in all the way ... otherwise it goes out.
  • #7 17030927
    barton21
    Level 26  
    What color of the candle? What mileage of the scooter?
  • #8 17033007
    paweld69
    Level 28  
    Mixture adjusted? Mixture screw how many turns has been screwed out?
  • #9 17036061
    Tom2602
    Level 3  
    The candle is the color of coffee with milk ...
    The mileage is not all 8,000 kilometers.
    The ring of the candle shows that the carburetor is rather well positioned. And the more so because it burns to the touch, whether warm or cold, there is no problem with it. It turns into normal, only there is a problem with descending to slow ...
  • ADVERTISEMENT
  • #10 17036184
    barton21
    Level 26  
    Check valve clearance. It should be 0.05 on suction and 0.08 on exhalation. If 8,000 has mileage without repairs, it is very much for a 4t scooter (if it is Chinese.)
  • ADVERTISEMENT
  • #11 17037201
    Tom2602
    Level 3  
    The valves were regulated as you write ... the head was put on a new one in December before Christmas and the valves were lapped because even though the head was new, the valves let go a little ... the pressure is very good.
    There is no problem with launching whether it is warm or cold ...
    And I think that such a mileage is not much because I had a zippa vapira before, he lived to 47 thousand kilometers without repair ...
  • #12 17040107
    Tom2602
    Level 3  
    Does anyone else have any ideas?
  • #13 17040302
    E8600
    Level 41  
    Only after firing it is this way?
    "Tuning" rollers / variator parts were not installed by any chance?
  • #14 17040745
    RafalGT2
    Level 24  
    Diaphragm in carburetor checked? is she okay not pruning? It happened the same after replacing the head? Was anything else replaced? What nozzle sits in the carburetor, as you know, after a certain mileage, you need to adjust the carburetor of experience, I know that sometimes in 4t Chinese, after a certain mileage, you need to change the nozzles.
  • #15 17040821
    Tom2602
    Level 3  
    The scooter comes off the revolutions, regardless of whether it is warm or cold, and it does not affect whether it is immediately after firing or if it comes a bit ...
  • #16 17040890
    barton21
    Level 26  
    Check that the choke is working properly
  • #17 17041206
    Tom2602
    Level 3  
    The suction works because the scooter starts at higher speed and after about a minute it goes down slowly.
Reply | New topic
Report a violation of the law

Topic summary

✨ The discussion revolves around a 4t scooter experiencing issues with its RPMs, particularly when descending from high revolutions. The user reports that the scooter maintains high RPMs when accelerating but drops to 4,000-4,500 RPMs upon releasing the throttle, eventually stabilizing at 2,000 RPMs. Various potential causes are suggested, including air leaks in the carburetor, throttle cable issues, and the condition of O-rings. The user confirms that the carburetor has been cleaned and O-rings replaced, but symptoms persist. Additional checks recommended include valve clearance, mixture adjustment, and the condition of the carburetor diaphragm. The user notes that the scooter starts well and runs normally, but struggles with RPM drop regardless of temperature or time after starting.
Generated by the language model.

FAQ

TL;DR: If your 4T scooter hangs at 4–4.5k rpm, set valves to 0.05/0.08 mm and "Check valve clearance." Fix intake leaks, enricher, and pilot jet; they cause lean idle hang. [Elektroda, barton21, post #17036184]

Why it matters: This FAQ helps 4-stroke (GY6/CVK) scooter owners quickly diagnose and fix slow-return revs for safer, smoother riding.

Quick Facts

  • Typical hot idle for many GY6/4T scooters: approx. 1,700–1,900 rpm. [“Kymco Agility 125 Service Manual”]
  • Valve clearances often used: intake 0.05 mm, exhaust 0.08 mm (cold). [Elektroda, barton21, post #17036184]
  • Mixture (fuel) screw baseline: about 1.5–2.5 turns out from lightly seated. [“GY6 Carburetor Tuning Guide”]
  • Two key intake seals: O-ring under the ebonite spacer and O-ring in the intake manifold—replace both. [Elektroda, barton21, post #17028612]
  • Auto‑choke (bystarter) begins leaning within ~60–90 seconds and extends fully in ~2–3 minutes. [“Keihin CVK Bystarter Operation”]

Why does my 4T scooter hold 4–4.5k rpm after I close the throttle?

A hanging idle points to a lean condition from unmetered air. Common culprits are intake leaks at the manifold, spacer O-rings, or cracked vacuum hoses. As one expert put it, “Usually, the problem is with the left-hand air that gets on the carburetor connection.” Fix sealing first, then fine-tune the carb. [Elektroda, 1133, post #17022173]

How do I check for intake leaks on the intake side?

Do a quick leak hunt:
  1. Inspect the intake manifold, ebonite spacer, and both O-rings for cracks, flat spots, or nicks.
  2. Wiggle vacuum hoses at idle and listen for RPM change; replace any brittle lines.
  3. Lightly clamp suspect vacuum lines briefly to isolate circuits. Replace any damaged seals and re-test idle. [Elektroda, barton21, post #17028612]

The throttle snaps back; can the cable still be the issue?

If the cable and linkage return fully to the stop, the cable is not holding revs. Verify correct routing, adequate free play, and smooth action with the seat off. Lubricate if needed. If the butterfly or slide closes, focus on air leaks, idle mixture, and the auto‑choke. [Elektroda, Staszek49, post #17023662]

What mixture screw baseline should I use on a stock CVK carb?

Start at about 1.5–2.5 turns out from lightly seated. Warm the engine. Set idle speed, then turn the mixture screw for the highest, smoothest idle and reset idle speed. If you need less than one or more than three turns, change the pilot jet size. [“GY6 Carburetor Tuning Guide”]

How do I set idle speed correctly on a GY6/4T scooter?

Set hot idle near 1,800 ±100 rpm using the idle-speed screw, not the throttle cable. Adjust with lights on to simulate electrical load. Use a tach if your dash lacks one. Correct idle speed shortens return-to-idle time and stabilizes fueling. [“Kymco Agility 125 Service Manual”]

Can the auto‑choke (enricher) cause a hanging idle, and how do I test it?

Yes. A stuck or weak enricher alters fueling during warm-up. Test it off-bike: apply 12 V to the leads and measure plunger travel over 2–3 minutes; look for roughly 3–5 mm extension. Refit with a good O-ring and confirm it seats in the carb. [“Keihin CVK Bystarter Operation”]

Could a torn carb diaphragm cause a slow rpm drop?

Yes. A pinholed or stiff CV diaphragm can let the slide hang and delay return to idle. Inspect the rubber for cracks and ensure the lip seats evenly in the cap. Replace the diaphragm or cap assembly if damaged. [Elektroda, RafalGT2, post #17040745]

What valve clearances help avoid hot‑idle issues on these engines?

Set the intake to 0.05 mm and the exhaust to 0.08 mm on a cold engine. Incorrect clearances can alter vacuum and idle behavior. As advised in-thread: “Check valve clearance.” Recheck after any top-end work. [Elektroda, barton21, post #17036184]

My scooter only idles if the idle screw is fully in—what does that indicate?

The pilot circuit is too lean or restricted. Remove the carb, clean the pilot jet and idle passages, and confirm the fuel-screw tip, spring, washer, and O‑ring are present. Reset baseline and fine‑tune. Consider upsizing the pilot jet if adjustment range is exhausted. [“Keihin CVK Service Manual”]

Do variator rollers or the clutch cause high idle hang?

CVT parts set gear ratio under load; they do not set idle speed. With the throttle closed, the engine should drop to the carb’s idle setting regardless of roller weight. Edge case: a dragging clutch can spin the wheel at idle but won’t hold engine rpm high. [“CVT Tuning Basics”]

My plug is coffee‑with‑milk color; is the mixture OK?

Tan color indicates overall mixture is close at cruise or load. It does not confirm the idle circuit. Idle can still be lean and cause a hanging idle. Evaluate after an extended idle-only run, or tune using RPM response and mixture screw behavior. [“NGK Spark Plug Reading Guide”]

After replacing the manifold and O‑rings, what else should I inspect?

Confirm the airbox-to-carb boot and clamps seal tightly. Check all vacuum lines, including petcock and emissions hoses. Verify the carb top cover seal and slide movement. Recheck mixture screw parts and pilot jet size. Ensure the auto‑choke fully extends and seals its seat. [“Keihin CVK Service Manual”]
Generated by the language model.
ADVERTISEMENT