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." :pinch:

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." :pinch:

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! :shifty:


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 .......... :innocent:

[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 :sunny:

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.

[CookMySock]

I've got some collets. I have a whole spare head or two. I just have to remove the head to swap the bits over, and I wasn't looking forward to that.

Both heads look in great nick. I'll replace the collets, unless the valve stem is stuffed as well, then I'll swap parts to get a good head. This, plus the other stuff required, turned our cheapie into a pricie, but three and a bit k is still not too bad over for a low km comet, and its plenty tidy.

Can these metal head gaskets be re-used or MUST they be hiffed out?

Steve

[CookMySock]

Ok I swapped the head for a known-good one, and replaced the faulty inlet rubber pipe, welded up an exhaust leak, and shit its smooth now... sounds like a new bike.. looks like one too. The metallic noise from it was defintely the faulty valve, and the weird idle was the broken inlet.

Replacement front brake disc to fit tomorrow, headlight fixed, and off for its WOF recheck.

Woohoo, it's fun working on bikes! Thanks for the help, people.

Steve

[RDjase]

I have heard stories about using compressed air to hold the valves shut, but I don't know if I am up for that.

Steve


Used to do it heaps when i worked at a engine reconditioners and doing valve seals with head still on, Bloody tight fit on most of the twin cam 16 valve car engines and some you just couldnt do, 4.1 falcons were easy lol. It wouldnt be worth the stress on a bike engine with 125cc per cylinder,

Good you got it sorted steve, It must have had a big over rev to do that to a low KM engine, Valve bounce?

[CookMySock]

Thanks man.. it was good fun. Got WOF and rego for it today so its all good for summer touring I think.


It must have had a big over rev to do that to a low KM engine, Valve bounce?Over rev will do that? ok..

The collets seemed to be in place.. just one was a little chewed.. I bet the valve stem was poked as well. That head is in the spare parts bin now.. carefully marked with the paint marker so no one uses it for something important.

Cheers!
steve

[RDjase]

Thanks man.. it was good fun. Got WOF and rego for it today so its all good for summer touring I think.

Over rev will do that? ok..

The collets seemed to be in place.. just one was a little chewed.. I bet the valve stem was poked as well. That head is in the spare parts bin now.. carefully marked with the paint marker so no one uses it for something important.

Cheers!
steve

When they over rev they can get valve bounce and the valves stays down AFTER the cam lobe has gone back up. When the valve catchs up and closes it hits the cam and cam followerbbucket and shim and gives the valve, cam follower and collets arseholes. The collets can jump out of the retainer and munt them and go back in the next valve opening(if your lucky) Dropped valves get real messy

[CookMySock]

When they over rev they can get valve bounce and the valves stays down AFTER the cam lobe has gone back up. When the valve catchs up and closes it hits the cam and cam followerbbucket and shim and gives the valve, cam follower and collets arseholes. The collets can jump out of the retainer and munt them and go back in the next valve opening(if your lucky) Dropped valves get real messyAhh I see.

Yeah I bought a bike that had dropped a valve. Feast your eyes.. LOL
http://www.kiwibiker.co.nz/forums/showthread.php?t=111271

Steve

[Voltaire]

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

Have you checked the tank, sometimes you get 'flakes' of rust that go into the 'cone' filter.I suggest you whippy off the tank and flush it.

[CookMySock]

after 20 years of the same old jokes, you have no idea how old they get.. Heard them all.. :yawn:

Steve

[RDjase]

Ahh I see.

Yeah I bought a bike that had dropped a valve. Feast your eyes.. LOL
http://www.kiwibiker.co.nz/forums/showthread.php?t=111271

Steve


Oops, I have never had that problem with my Yamaha 2 strokes lol, Suzuki's tho, RGV's and there power VALVES :bash: