GT186 / Series 2 / PHBH 30 / TSR Evo - Sudden Rough Running

[Donnie]

So, been going fine since I built this engine, other than my burning the clutch and having to redo that etc.

So, going fine, done the jetting running well other than a soft seize where I tweaked the jetting again and no problems, if anything slightly rich until opening it right up.

However, after a few weeks of no issues Ive suddenly developed a low speed bweaaaahhhhhhburbleyburble which i estimate at about a quarter throttle, like its missing a beat but open her up and it dissappears.
Now, that morning id put some petrol in from a can stored in the shed for a week or so and assumed it was that.

Actions so far:
Drained and refilled with fresh fuel and oil - no difference.
Thinking it's a load issue changed the cdi, lead, ht cap and spark plug - no difference.
left kill switch unplugged thinking a loose earth - no difference
Just stripped, cleaned (didnt need it) carb and rebuilt it and now wondering what's left??

I can only think its worth restrobing the timing or / checking reed petals?

Anyone got any other thoughts before I delve into that?

[MickYork]

Stator/pick up ?

[Donnie]

Ah good point, missed that was thinking too far ahead! I can do that with only disconnecting a couple of wires! Back in 5

[Donnie]

Done it, white to mag housing - short circuit as it should

white to red (pickup expected reading 95-120ohms) reads 94-95 so on lower end of normal and same as when built.

white to green (LT Coil expected reading 450-540ohms) reads 455 and again same as when built.

Bugger, not that either then.

I cant see it being the reed petals as surely it would simply get worse on acceleration?

[MickYork]

once had a pick up that was loose. only caused a problem in a certain rev' band.

Slim chance but worth checking.

[coaster]

Reeds ok? and seeing as you have had a seize, what's the compression like? just wondering if a ring has got stuck in its groove?

[Donnie]

once had a pick up that was loose. only caused a problem in a certain rev' band.

Slim chance but worth checking.

Slim but never know so will have to physically check it after tomorrows shift.

[Donnie]

Reeds ok? and seeing as you have had a seize, what's the compression like? just wondering if a ring has got stuck in its groove?

compression never altered and its been running spot for a few weeks since that happened and suddenly its now misbehaving. Ill check the reeds though

[Meds]

Is your choke cable being tensioned as the engine swings.
Mine was rubbing on the toolbox and causing the choke to pop on slightly
It was only evident when pulling away.
I found it by accident, noticed the rubbing on the toolbox, stuffed in a flip choke and he problem disappeared.

[burnside]

Did you double up the reeds? Rich T recommends this if using an expansion on the 186 kit

[Toddy]

The stator can be faulty under load , usually it breaks down completely then after cooling down will re start so can't be checked when standing , just a thought

[Wack]

Put some marks on your throttle grip and switch housing then ride it and see where the bad spot is.Then try dropping the needle one notch to see if the rough spot clears,it may be a worn needle and atomiser.

[johnnyjarvis]

What Wack said.Best £20 Ive ever spend on my scooter.
Had the same problem a couple of years ago. Changed and tested everything and finally bought a new atomiser and needle.
Smoother than a smooth thing.

[Donnie]

Is your choke cable being tensioned as the engine swings.
Mine was rubbing on the toolbox and causing the choke to pop on slightly
It was only evident when pulling away.
I found it by accident, noticed the rubbing on the toolbox, stuffed in a flip choke and he problem disappeared.

Nope not that either, checked it.

[Donnie]

Did you double up the reeds? Rich T recommends this if using an expansion on the 186 kit

I haven't actually but IF that was the cause why would it only now be an issue after several hundred miles?

[Donnie]

The stator can be faulty under load , usually it breaks down completely then after cooling down will re start so can't be checked when standing , just a thought

That's usually only the old "wont restart when hot, but does from cold" scenario isn't it? ie the heat expands the cracked wire and it stays "broken" until it's cooled?

[Donnie]

Put some marks on your throttle grip and switch housing then ride it and see where the bad spot is.Then try dropping the needle one notch to see if the rough spot clears,it may be a worn needle and atomiser.

It's not, new needle and atomiser in there and new slide too.

[Toddy]

The stator can be faulty under load , usually it breaks down completely then after cooling down will re start so can't be checked when standing , just a thought

That's usually only the old "wont restart when hot, but does from cold" scenario isn't it? ie the heat expands the cracked wire and it stays "broken" until it's cooled?

It is but can cause similar symptoms to yours

[Donnie]

Hmm worth bearing in mind, but this is doing it straight from cold too?

Just had the flywheel off to physically check stator, nothing loose, all wires look good, almost hoped there would be something broken and obvious.

Next step is the reeds i guess

[Adam_Winstone]

Never trust a stator, which can appear fine and give correct readings, but reeds are a good shout too.

Good luck getting to the bottom of it.

Adam