Seemingly healthy 125cc misfires a lot and is unusable

[mistermentali...]

I have a Hn125-8. It is a single four stroke engine and has a misfire which means I cannot use it as it stalls while idling and once stalled is a pain to get to restart. The misfire seems to be a regular misfire not just a random one and at higher speeds I get a slight chugging which I attribute to the misfire.

It will idle lovely but then just misfire and sometimes the misfire stalls the engine while idling.

I have tried changing the idle mix, tried a new ignition coil and new cdi and new spark plug and nothing makes any difference. I have checked the tappets and they are fine.

I am hoping someone can advise me what could be the cause as at the moment I think I will have to buy a new stator as that has a timing coil (pickup coil / timing pickup) included and thats the only thing I havent changed yet, aside from the regulator rectifier, that may affect ignition.

The battery seems fine and charges no problem and there are no damaged or corroded wires so am really baffled and hate having to get to work on the bus as its over two hours each way on bus and only 45 mins on bike so very keen to sort the problem as you can imagine.

Thanks,
Dave

[jaffa90]

Sounds similar to an Enfield i had and it was the kill switch connection.

[mistermentali...]

Thats something I haven't considered although the kill switch works properly and it looked ok internally when I had the kill switch assembly out a few months back putting in the throttle cable.

Will have to check for that issue just to be sure. Thanks for the suggestion.

[Nobby the Bastard]

Stalling at tickover is symptomatic of an air leak in the intake between the carb/FI and the head.
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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

[mistermentali...]

Checked kill switch just now but seems fine.

Have checked for air leaks but found none so thankfully can rule that out.

It only stalls at the same moment that it misfires, but not on every misfire. Its very strange because it will idle lovely and then when it misfires sometimes it will stall and the other times the revs will almost die but the bike will not quite stall and carries on idling.

I don't earn a lot so am reluctant to buy more parts if not needed as wasted money on new carb and cdi and coil, but am leaning toward getting new stator and just hoping it fixes problem. But at the back of my mind I am doubting the pickup coil attached to the stator would go faulty, if it did I would expect a much worse and random misfire but I know nothing about the coil does could be totally wrong.

[Rogerborg]

90% of fuelling problems are electrical.

The first thing I did on my HN125-8 was to unbolt the sidestand switch and move it and its wiring up under the seat. I'd have a look at yours, particularly the inexplicable connector block placed right under the engine in a prime location to corrode.
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Biking is 1/20th as dangerous as horse riding.
GONE: HN125-8, LF-250B, GPz 305, GPZ 500S, Burgman 400 // RIDING: F650GS (800 twin), Royal Enfield Bullet Electra 500 AVL, Ninja 250R because racebike

[mistermentali...]