2 Stroke 50cc (Aprilia) revs rising by itself

[bcflogic]

2017 Aprilia SX50. Stock carb/jets *I believe*. Starts from cold 100%. Idles fine/revs fine. However, after approx 1 min, when a tweak of the throttle, the revs rise to almost max and stick. It's not a stuck throttle cable that I can see.

After a few seconds they come back down again and the bike will ride 100%. When the bike is then switched off/re-started 1 min later the EXACT same thing happens.

If it was an air leak, surely it would do it all the time? I can't understand why it does it once only after 1 min and then is fine again until the engine is stopped/restarted then happens again.

Any advice appreciated.

[Robby]

If it only happens on a cold engine and at about the same time, I would be looking for a problem with the choke. I assume it may even have auto-choke, being a fairly new 50cc.

It's a 50 and it isn't brand new, so assume someone has fucked with it in a totally idiotic way.

[Zen Dog]

That is a weird one. If it was only when it was cold you might think it was a sticky carb slide that loosened up when warm or something, but every time even when warm? No idea.

Robby's suggestion seems like an avenue worth pursuing.
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Current - '94 VFR750FR (Dead), '00 VFR800FI, 2011 CBF125 Previous - '10 Street Triple R, '92 MZ ETZ301, '05 TTR250, NSR125R, KMX125, "Honda" Win (chinese copy of an old Honda design with a C90 engine)
My bike trip around S.E. Asia 2010/2011

[bcflogic]

It happens when warm too, every time. It has a manual choke. I think it's time to strip the carb.

[Nobby the Bastard]

Hmmm.

Is it incredibly rich or lean and is actually only just idling at what should be a high idle carb slide position and as soon as you touch the throttle it gets into a more efficient/effective fueling range and so accelerates upwards?
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trevor saxe-coburg-gotha:"Remember this simple rule - scooters are for men who like to feel the breeze on their huge, flapping cunt lips."
Triumph Sprint ST 1050

[Robby]

Air leaks don't always behave like you want them to.

Check it all over. Something will be put in the wrong way round, a rubber will folded over or split, or a gasket split.

I once managed to cause an air leak by putting a carb spacer in the wrong way round. They're bastard things to track down.

[bcflogic]

Could be. I will whip the carb off and take a look.

[dave001]

has it been standing just wondering if its a combination of a gummed up jet and if going lean when the auto choke comes off

id check the plug and pull the carb and clean and blow out jet with airline and check for a air or vacume leak