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[Solved] 2t Scooter - Starting Up Successfully but Stalling After Increasing Gas Input

Królik1981 48510 18
Best answers

Why does my 2T scooter start and idle, but stall when I open the throttle?

Check the carburetor/needle setting first, because a black, wet spark plug points to a too-rich mixture; lowering the needle can lean it out, and the ignition may also be set too late [#17349908][#17349984] If the scooter still will not pull past idle, the forum later found the real fault was mechanical in the CVT: the variator sleeve had play and the rollers were too heavy [#17503556] Replacing the variator and fitting 4 g rollers fixed the problem and the scooter started running normally [#17503556][#17503786]
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  • #1 17347590
    Królik1981
    Level 10  
    Posts: 95
    Help: 2
    Rate: 41
    Hello, I have a problem with my 2t.It fires from the shot at idle speed, it goes out beautifully after adding the gas? Will you help?
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  • #2 17348203
    jakubek56
    Level 32  
    Posts: 1630
    Help: 202
    Rate: 453
    Is the carburetor properly adjusted?
  • #3 17349073
    Królik1981
    Level 10  
    Posts: 95
    Help: 2
    Rate: 41
    I guess so? I adjusted with these two screws, and is there any other adjustment?
  • #4 17349129
    Zygaqra
    Level 35  
    Posts: 2234
    Help: 257
    Rate: 494
    You are a weak scooter repairer if you open the topic with such a problem and with errors (not mine) and what are you shooting? Blind people, I guess. Give the engine a moment to work and check the candle, its color will tell a specialist everything, or maybe the candle needs to be changed at all.
  • #5 17349290
    Królik1981
    Level 10  
    Posts: 95
    Help: 2
    Rate: 41
    Weak, therefore, I am asking for help, the candle is new when I turn black

    Added after 4 [minutes]:

    Black and slightly damp, I know it should be dry and brown, the spire is on the other notch
  • Helpful post
    #6 17349908
    Zygaqra
    Level 35  
    Posts: 2234
    Help: 257
    Rate: 494
    Did the engine warm up when you put out to check the candle? The engine should run smoothly without any gauges, if this is what the candle looks like, you would have to lean the mixture by lowering the needle. It is also worth checking the ignition, it may be too late
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  • #7 17349984
    Anonymous
    Anonymous  
  • #8 17351821
    Królik1981
    Level 10  
    Posts: 95
    Help: 2
    Rate: 41
    The hot engine, I changed the needles to the bottom, i.e. the clasp at the top did not help. And how do you set the ignition correctly?
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    #9 17355106
    Zygaqra
    Level 35  
    Posts: 2234
    Help: 257
    Rate: 494
    Exactly and as much as the manual for this engine says. There is no single advance angle for all engines. I would like to add that it accelerates towards the turnover, but as it is your permanent job, you probably know it well.
  • #10 17355113
    SKM 1964
    Level 34  
    Posts: 2191
    Help: 150
    Rate: 660
    Rather, modern scooters have no ignition advance control. Usually a pulser set permanently at the factory. But the author does not specify the scooter model ?? :|
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    #11 17355119
    Zygaqra
    Level 35  
    Posts: 2234
    Help: 257
    Rate: 494
    Exactly and as much as the manual for this engine says. There is no single advance angle for all engines. I would like to add that it accelerates towards the turnover, but as it is your permanent job, you probably know it well.
  • #12 17355140
    Królik1981
    Level 10  
    Posts: 95
    Help: 2
    Rate: 41
    The scooter is a junak 606 and is the ignition setting in the module in this scooter? Because I read the statements of other guys and I wonder, maybe the module has fallen?
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    #13 17355813
    SKM 1964
    Level 34  
    Posts: 2191
    Help: 150
    Rate: 660
    As long as it has a good quality module, the ignition is switched electronically
    depending on RPM and instantaneous acceleration. In 2T it is not big, but in 4T it is much bigger, so it should not change modules. :|

    Added after 15 [hours] 8 [minutes]:

    In addition, each other engine has a different ignition angle and requires a different ignition acceleration map if the module allows it. A colleague wrote about it above. :|
  • #14 17495963
    Królik1981
    Level 10  
    Posts: 95
    Help: 2
    Rate: 41
    Gaznik managed to adjust the candle after warming up coffee with milk, it turns beautifully on the legs on the legs, while driving, max speed 4500 vmax 40km uphill no power, I will add that I thought the piston? So I put on a new piston rings and cylinder, unfortunately no improvement
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    #15 17497147
    SKM 1964
    Level 34  
    Posts: 2191
    Help: 150
    Rate: 660
    Replace the ignition module. Maybe yours is with a turnover limit ?? Yes, not to exceed 45 km / h. :|
  • #16 17497171
    Królik1981
    Level 10  
    Posts: 95
    Help: 2
    Rate: 41
    I have already ordered a new module, I have a question, if the module is blocked, why is it spinning to the maximum speed on the legs?
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    #17 17502926
    SKM 1964
    Level 34  
    Posts: 2191
    Help: 150
    Rate: 660
    If it is blocked, it will not screw in all the way, it will just cut the ignition off and keep the engine from running higher. :| And it doesn't matter if it's loaded or not. :|
  • #18 17503556
    Królik1981
    Level 10  
    Posts: 95
    Help: 2
    Rate: 41
    So mine is unlocked if the legs are spinning normally. I changed the modol and it's the same, I heard that some scooters have 2 masses? Someone knows something about this?

    Added after 2 [hours] 26 [minutes]:

    It turned out that the vario sleeve had slack and the rollers were too heavy, I changed the vario and put on the 4 g roll, it flies like a smear, thanks and greetings
  • #19 17503786
    Królik1981
    Level 10  
    Posts: 95
    Help: 2
    Rate: 41
    So mine is unlocked if the legs are spinning normally. I changed the modol and it's the same, I heard that some scooters have 2 masses? Someone knows something about this?

    Added after 2 [hours] 26 [minutes]:

    It turned out that the vario sleeve had slack and the rollers were too heavy, I changed the vario and put on the 4 g roll, it flies like a smear, thanks and greetings

    Added after 1 [minutes]:

    Change vario and lighter rollers
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Topic summary

✨ The discussion revolves around a 2-stroke scooter that starts well but stalls when gas is increased. The user initially suspects carburetor issues and receives various suggestions, including checking the carburetor adjustment, inspecting the spark plug, and verifying the ignition timing. The spark plug appears black and damp, indicating a rich fuel mixture. Users recommend leaning the mixture and checking the ignition advance angle. The scooter model is identified as Junak 606, and it is noted that the ignition module may be electronically controlled. After several adjustments, including changing the piston rings and cylinder, the user discovers that the variator sleeve was loose and the rollers were too heavy. After replacing the variator and using lighter rollers, the scooter performs well.
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FAQ

TL;DR: On a 2T Junak 606 that stalled on throttle, 4 g rollers fixed it; "the vario sleeve had slack and the rollers were too heavy." Start with plug reading and carb checks, but inspect the CVT early. [Elektroda, Królik1981, post #17503556]

Why it matters: This helps 2T scooter owners fix start-then-stall and low‑RPM under‑load issues without wasting money on the wrong parts.

Quick Facts

Why does my 2T scooter start then stall when I open the throttle?

It’s either over‑rich fueling or the CVT keeping RPM out of the powerband. Read a warm plug to confirm mixture. If fueling is fine, inspect the variator bushing and roller weight. Heavy rollers or worn sleeves hold RPM down under load. In the Junak 606 case, a fresh variator and 4 g rollers restored pull. "It flies like a smear" after the swap. [Elektroda, Królik1981, post #17503556]

What does a black, wet spark plug tell me?

Black and wet means a rich mixture and poor combustion. Warm the engine before reading the plug. Correct fueling before replacing ignition parts. "Black and wet candle is too rich a mixture." If it stays sooty after tuning, check float height and auto‑choke operation. [Elektroda, Anonymous, post #17349984]

Should I read the spark plug hot or cold?

Hot. Run the engine, kill it, then remove the plug. A cold plug reading misleads diagnosis. Make mixture changes only after a proper warm‑up ride. If midrange is rich, lower the needle by raising the clip one notch. Re‑test under load. [Elektroda, Zygaqra, post #17349908]

Which carb screws do I adjust, and how?

Most scooter carbs have an idle‑speed screw and a pilot mixture screw. Tune only when fully warm.
  1. Set idle speed to spec with the throttle‑stop screw.
  2. Turn the mixture screw to peak idle, then fine‑tune slightly richer.
  3. Reset idle, test ride, and read the plug. This restores clean off‑idle response. [Keihin CVK Tuning Guide]

Can late ignition timing cause bogging on a 2T scooter?

Yes. Retarded advance reduces torque and can cause stalling when you open the throttle. With these symptoms, verify ignition advance early in diagnosis. If it’s late, correct the cause, such as CDI or pickup position. Re‑test after confirming mixture. [Elektroda, Anonymous, post #17349984]

Can I adjust ignition timing on a Junak 606 2T?

There’s little user adjustment. A quality ignition module controls timing electronically by RPM and acceleration. Two‑strokes use modest advance variation compared to four‑strokes. Use the correct CDI and pickup for the engine. Avoid random module swaps without a matching map. [Elektroda, SKM 1964, post #17355813]

How do I tell if my CDI is speed‑limited?

A restricted CDI cuts ignition at higher RPM, so the engine stops revving out smoothly. You feel cyclic misfire at the top. This behavior is independent of load and appears on the stand too. That confirms a limiter is active. [Elektroda, SKM 1964, post #17502926]

My scooter only reaches ~4500 rpm and ~40 km/h under load. What next?

Inspect the CVT first. Low RPM under load points to heavy rollers, a worn variator bushing, or belt slip. In the case discussed, the plug was tan after tuning, yet speed stayed ~40 km/h with ~4500 rpm. Swapping the top end didn’t help, confirming a transmission issue. [Elektroda, Królik1981, post #17495963]

Why didn’t replacing the piston and cylinder restore power?

The fault was in the transmission, not the top end. Roller mass and a loose variator sleeve kept the engine from reaching powerband. A sound variator plus 4 g rollers restored acceleration and speed. Fix the CVT before opening the engine. [Elektroda, Królik1981, post #17503556]

What roller weight fixed this Junak 606, and what does weight change?

Four‑gram rollers solved the bog by letting RPM rise before upshifting. Lighter rollers raise revs; heavier rollers lower revs. Choose a weight that holds peak torque during acceleration. Tune in small steps to avoid over‑revving and belt slip. [Elektroda, Królik1981, post #17503556]

If it revs to max on the stand, can the CDI still be restricted?

No. A limiter cuts ignition regardless of load, preventing full revs even on the stand. If it revs cleanly unloaded, investigate CVT and fueling instead. That observation rules out a speed‑limited CDI. [Elektroda, SKM 1964, post #17502926]

What’s a fast, low‑cost diagnostic order for start‑then‑stall complaints?

Warm the engine and read the plug first. If rich, lower the needle by moving the clip up one notch. Test again under load, then consider ignition checks if symptoms persist. This sequence isolates fueling before electronics. [Elektroda, Zygaqra, post #17349908]
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