Hyosung 250 strange idle

[CookMySock]

Just picked up another Comet 250, and it has an irregular idle, like it has a spark plug lead off, but one time in ten you can hear it pick up and come right. I thought it was carb balance, but its not. Also if I let it sit and idle until its good and hot, the problem seems to be not so noticeable.

From cold start, the front exhaust runs barely warm and the rear runs hot.

There is a ticker-ticker valve-gear noise that runs continuously. It's not particularly bad.

I ditched the old fuel out of it and drained the carbs.

It almost sounds a faulty ignition lead.

The bike rides perfectly well and has plenty of power, but will quit at stop signs if I blip the throttle just right. If I idle it down carefully, it will idle quite happily.

Any suggestions before I start swapping bits around? I was gunna swap ignition from front to rear and so on.

Many thanks in advance.

Steve

[gatch]

Does hyosung use cv carbs ?

[CookMySock]

Does hyosung use cv carbs ?

Pretty sure these are CV carbs.

Steve

[hayd3n]

check the plugs??

[CookMySock]

check the plugs??

I haven't but I will. It's a modern four stroke engine with low kms - I'd be very surprised to find a fouled plug, and if I did, it would reveal other major issues, so I hope its not that.

The bike has been sitting around for a year, so maybe it needs a carb strip, though I think this is the reason it hasn't been used.

Steve

[CookMySock]

Dropped by the bike mechanic this morning, and he doesn't like it. "Cam or piston, or both."

Not happy. Off comes the head.

Steve

[Hiflyer]

Dropped by the bike mechanic this morning, and he doesn't like it. "Cam or piston, or both."

Not happy. Off comes the head.

Steve

And out goes your eftpos card! haha

Good luck man, hopefully it's not too bad

[CookMySock]

Ok front cam cover off - this is the cylinder thats missing. All looks VERY clean and tidy.

Valve clearances are all .006" EXCEPT for the right-side exhaust valve, which is too tight to fit any of my feeler guages under. Why would it have done this?

What if I whip cam out, pull bucket, try different shim, or polish a wee bit off the shim?

TIA
Steve

[boostin]

Let me get this straight. Before you will change a spark plug, you will take the head off?

[CookMySock]

Let me get this straight. Before you will change a spark plug, you will take the head off?

Re-read. The engine is brand new. 8,000km. Too busy doing interesting things to argue.

Steve

[AllanB]

The engine is brand new. 8,000km.

Steve u got ripped - 8,000 kms is not brand new, it's just low kms!


What's with you and these Hoyosumz, you just can't keep away from them!


I'd start with spark, but since the valve cover is off reset that tight one with a new shim - you'll want a smaller one than the existing work out the differences you need to get the setting right. Agent should have heaps of them - or nick one out of that bike you are selling ..........

[CookMySock]

Ok found something. One of the valve spring retainer clips is looking pretty munted. My guess it was just around ready to let go and drop its' valve. Yum.

To appease certain members, I pulled the park plug out and had a look at its perfectly ok.

The shim is looking plenty chewed from where little bits if retainer clip have got under it and had a wee bite.

Anyway, I have a complete spare head (40,000km) that looks usable. I don't like my chances of getting that retainer collect clip thingy out from under the valve spring while the head is on, so the head has to come off regardless. I have heard stories about using compressed air to hold the valves shut, but I don't know if I am up for that.

Swap the head with the good spare? Or pull the head and put another clip in place from the spare head?

Starting to pull the head off...

Steve

[CookMySock]

Also found a carb boot to be completely stuffed. That accounts for the miss, and the valve accounts for the rattle.

Ordering parts.

Steve

[AllanB]

Why replace a 8,000 km head with a 40,000 km one?

I'd use the existing head - you can always take it to the mechanic to fix the faulty clip - won't be much as you have done the time consuming work pulling the head of.

8,000 kms - faulty spring clip, carby rubber ...........

Fix it, sell the bike and buy a Honda

Or a Ducati if you like your V-twins, Sv650 etc

[xwhatsit]

Are spring clips just like the little collets that hold the retainer on the top of the spring? Aren't they about $5-10 or something? It'd be pretty easy to just buy a new spring clip, lap the valves, stick it back together.