Revs drop away for 1/4 second or so in top gear

[rf74]

hi everyone.

wondering if someone can give me a clue or two as to whats going on with my bike.
I've got a 2003 Hyosung GT250 - its been an excellent bike to me so far but...

The last week or so its done the following a couple of times. Not every time I ride it the 22kms or so to work, but just sometimes:
When riding at 90-100kmh, in 5th gear, the revs will drop by about 500rpm for an instant - maybe a quarter of a second, certainly no longer. Its like the engine momentarily stutters or something. I actually saw this happening yesterday on the rev counter - its sitting on 7000 or whatever its revving at at 100kms, and then it momentarily dropped away to 6500 and then popped back up to 7000. I had the throttle open in the same position the whole time, and the bike was well warm by then as this happened over 10kms into my ride home.

So far i haven't seen this happen in any of the other gears, ie when riding in a 50kmh zone or anything.

Anyone have any ideas (constructive ones, I don't want inconstructive comments about Hyosungs please )

cheers

RF74

[WRT]

Was it raining at the time? You might be getting some water blown into the 'lectrics.

[johan]

maybe it's time for new spark plugs?

[riffer]

Your handgrip could be loose too, and spinning around a touch.

[skidMark]

Possibly stand moving in wind/ dodgy side stand switch, drown it in crc.

[scracha]

When riding at 90-100kmh, in 5th gear, the revs will drop by about 500rpm for an instant - maybe a quarter of a second, certainly no longer. Its like the


Buy an Italian bike mate...you get the same experience except it wheelies when the power kicks back in. In all seriousness, sounds like a misfire. Spray WD40 all over the @#$ckin shop (cue folks telling you WD40 is evil) and check your coils. I doubt it's just happening in 5th gear but you probably notice it more as that's the gear you cruise in.

[skidMark]

Buy an Italian bike mate...you get the same experience except it wheelies when the power kicks back in. In all seriousness, sounds like a misfire. Spray WD40 all over the @#$ckin shop (cue folks telling you WD40 is evil) and check your coils. I doubt it's just happening in 5th gear but you probably notice it more as that's the gear you cruise in.


Good points there, you probably wouldn't notice it until cruising along, i would also say new plugs as well as chances are the coils won't have gone yet, its not exactly an old bike.

It does sound like it's not firing for that split second so it's either plugs or something electrical, ie sidestand switch, unlikely but the things i saw as a mechanic, its silly shit like that sometimes.

[FilthyLuka]

REMINDER: Pointless bullshit will not be tolerated.

For once, i agree with Mark. Check the side stand switch and drown everything in WD-40, it does sound like the side switch cutting out.

Use the search function, someone had a similar problem a while ago and there is a thread about it somewhere in the depths of the Bike Mechanics forum.

But yeah, check all the electrical plugs and wiring, make sure none of the wires are broken or anything. Yank out the plugs and check the state of em, its easy enough. Silly question, does the engine stop pulling or is it just the tach bouncing about?

[Grub]

I actually saw this happening yesterday on the rev counter - its sitting on 7000 or whatever its revving at at 100kms, and then it momentarily dropped away to 6500 and then popped back up to 7000.

Ahhh ... that sounds like the Hyosung "emmission feature". I only learned about it here on KB and there's quite a thread on it if you try the Search Feature. Apparently this has been described as a "flat spot" and it is immediately fixed by removing a wire from the CDI unit. But I don't know which wire, I believe it was described with several links in that thread.

One of the "gotchas" is that models apparently from the same year have different looms - all is described there so see if you can track it down.

[rf74]

In reply to the many replies - thanks guys...


- It could be water in the electrics - the first time it happened it was raining lightly when I was riding from Wgtn to the Hutt on the way to my full licence practical test!!

- could be the spark plugs. i can pull them out - how can I tell whether they're stuffed or not?

- I doubt its the sidestand - when idling my bike before, I gave my sidestand a nudge in all directions and nothing happened.

- I'll try the WD40 - as it happens I bought a big can on the weekend. I've heard its good for lots of things, just not as a chain lubricant. And no, i'm not getting an italian bike. But I really likes the looks of the Bandit 650 or the SV650...

- I don't think / hope its the hyosung flat spot feature. I've had the bike for just under a year, and its been good til now.

cheers

R.

[FilthyLuka]

- I doubt its the sidestand - when idling my bike before, I gave my sidestand a nudge in all directions and nothing happened.


It will be a wee little switch somewhere, see if you can find the wires leading down to the stand.

[avgas]

REMINDER: Pointless bullshit will not be tolerated.
Oh come on i had a good laugh about it. Its derailing the ship that moves into PD - i don't see anything about jokes in a thread.
Besides these are all helpful hints - just not in the best medium.

[FilthyLuka]

Oh come on i had a good laugh about it. Its derailing the ship that moves into PD - i don't see anything about jokes in a thread.
Besides these are all helpful hints - just not in the best medium.

Ahem, the comment was directed at SkidMark and Katman, the posts to which i was refering have been PDed. If a post has even minor relation to the thread, then i don't mind, but katman and skidmark can bitch at each other elsewhere




This is a technical forum only so no drivel will be tolerated.

Do not complain if you find your posts deleted unless you believe it had technical value.


mmkay?

[Jantar]

If its only for a fraction of a second, it may be the rev counter, and not the actual engine output. A 500 rpm drop would equate to drop in speed of 7 kmh. To drop 7 kmh and pick it up again in a fraction of a second would require a lot more power than your 250 is capable of putting out.

Do you notice a definite drop in performance at the same time?

[rf74]

nah, its the actual engine output as well. Thats how I noticed it at first, its like a little blip or stutter in engine output, along with a corresponding dip on the rev counter meter.

It didn't do it on the ay home tonight. I'm going to take look at the spark plugs on the weekend, meantime I'll give it a good spray with the WD40 tomorrow morning

[Henk]

Plugs are cheap so replace them anyway but I doubt they are causing an intermitent problem. Check connectors wiring, battery terminals etc.
Fruiting about with the sidestand when you are sat still won't show up any possible problems as the sidestand switch usualy doesn't do anything unless you are in gear with the clutch out, hard to do when stationary unless you have the bike on a centerstand. Not familiar enough with Hyosungs to know if it has one if it has try wobbling the sidestand with the back wheel spining. If you put the stand down and the engine cuts out you haven't found the problem, everything is doing what it should.

[homer]

In reply to the many replies - thanks guys...


- It could be water in the electrics - the first time it happened it was raining lightly when I was riding from Wgtn to the Hutt on the way to my full licence practical test!!

- could be the spark plugs. i can pull them out - how can I tell whether they're stuffed or not?

- I doubt its the sidestand - when idling my bike before, I gave my sidestand a nudge in all directions and nothing happened.

- I'll try the WD40 - as it happens I bought a big can on the weekend. I've heard its good for lots of things, just not as a chain lubricant. And no, i'm not getting an italian bike. But I really likes the looks of the Bandit 650 or the SV650...

- I don't think / hope its the hyosung flat spot feature. I've had the bike for just under a year, and its been good til now.

cheers

R.

Test ride both the bandit and the sv before you make a decision