Jerky bike

[Grashopper]

Yesterday's ride was weird. First I made a typical beginner's mistake and drove off with the sidestand down and then I noticed that the bike was behaving weirdly. Unless I was strongly accelerating I could feel a slight jerky movement of the bike, like irregular fluctuations in power input (throttle was steady or slightly rolling though) or power output. Felt a bit like running out of fuel, but I was still about 50 km or so above the reserve.

Tried to do some research yesterday, but most of the technical stuff went far over my head. What I got from it so far, and please correct me if I got things wrong, is that it could be the following things:

- kinks in fuel lines
- dirty air filter
- loose battery connections
- that little battery overflow tube (http://www.kiwibiker.co.nz/forums/showthread.php/152465-Stuck-throttle-gn250/page2)
- spark plugs
- dirty carbs (and lots of other things that could be wrong here)
- chain (too loose, dirty, old)
- fuel anyway?

But not much I can really do with my limited mechanical knowledge, so the plan today is to fill him up, try to find fuel lines and see if they have any kinks and check that battery overflow pipe. Not much else I can do, maybe the air filter (still can't get over that the manual said to dump it in motor oil. Is that normal or a GN thing???), but I would be too worried to do something wrong or not being able to put things back together safely if I touch anything of the other things.

Anything else I could check easily?

[Laava]

So do all those things and drain the tank and put fresh fuel in and if it is still doing it then you should be able to get some more constructive help.


Someone will be along soon to enquire about your powerband colour and condition. Ignore them, unless you have a sense of humour in which case indulge them and, er, make sure you have topped up your indicator fluid!

[Dogboy900]

One other thing is the fuel filter. If you have an inline one it could be clogged or have a crack in it.
Had similar problem with a car years ago tried everything still had a problem. Turned out to be a small crack in the fuel filter that let air into the line when it warmed up. Worth replacing a $5 part just in case.

Good luck.

[Supertwin Don]

Before you start mucking around with motor - check that you haven't got a slightly binding brake - at either end!

[FJRider]

It sounds more like a dirty spark plug. But turn the fuel tap off, and remove the drain plug on the bottom of the carb bowel (usually a brass one). Let all the fuel drain from the carb then with drain plug off ... turn fuel tap on again and flush the carb for a few seconds. A large cloth rag under the carb to catch all the fuel is very good.
Look inside the tank and see if the inside of the tank is flaking ... which may block the filter in the tank. (the filter attached to the fuel tap. If you drain the fuel out ... take off the fuel tap and check that.

But my bet is with a dirty plug.

[craigdek]

Sounds to me like a plug or clogged carb jet. If it happens at higher speeds then I would check coils. Pull the plugs and wire brush them. Might find a plug coming apart when you remove it which would be the problem. Otherwise drain each carb. Take off cover. Clean out sump and blow out the main jet. Could be clogged. Obviously remove the main jet first. Don't mess with the diaphragms if they move fine above butterfly valve.

[Akzle]

chuck some gull ethanol through it (the expensive stuff - blue, i think the pump is) that's good at melting all the varnish and blowing it through your engine.
this is, of course, if fuel is getting to your engine.
pull the fuel line off the tap - will tell you if your tap is shat.
unscrew the drain at the bottom of your carbs - will tell you if you've got fuel in the bowls.

then, my guess, is go find a human with a penis, and tell them your carbs need cleaning and the floats set 1mm higher.

(putting oil on air filters is not uncommon)

-edit-
chain slack is eay to see - park bike, push midle of chain up, if you can push more than 2" it's too loose, if you can't push it more than 1" it's probably on the tight side. but from what you describe, this is not your problem.

[Katman]

Rather than paying much attention to the highly questionable/amusing advice being given in this thread you could always stop by the workshop and I can let you know what is wrong with it.

[bogan]

Yesterday's ride was weird. First I made a typical beginner's mistake and drove off with the sidestand down and then I noticed that the bike was behaving weirdly. Unless I was strongly accelerating I could feel a slight jerky movement of the bike, like irregular fluctuations in power input (throttle was steady or slightly rolling though) or power output. Felt a bit like running out of fuel, but I was still about 50 km or so above the reserve.

That it is fine at strong acceleration and jerky at cruise suggests it is a fuel/air mix issue imo. The simple things to do is check for air leaks on the inlet manifold (between carb and engine) and make sure the air filter is not clogged up (though this is less likely due to it being fine at 'strong' acceleration).


But not much I can really do with my limited mechanical knowledge, so the plan today is to fill him up, try to find fuel lines and see if they have any kinks and check that battery overflow pipe. Not much else I can do, maybe the air filter (still can't get over that the manual said to dump it in motor oil. Is that normal or a GN thing???), but I would be too worried to do something wrong or not being able to put things back together safely if I touch anything of the other things.

Anything else I could check easily?

Often with fuel/air mix issues it requires a bit of expertise or at least mechanical know-how.

[ducatilover]

Rather than paying much attention to the highly questionable/amusing advice being given in this thread you could always stop by the workshop and I can let you know what is wrong with it.
:niceone:
I suggest you do what this man said.
There can be many reasons why your GN acts like that (mine did it for many reasons... heap of shit) :rolleyes:

[haydes55]

Jerky bike

And here I was expecting a bike made out of jerky :confused:

[Haggis2]

And here I was expecting a bike made out of jerky :confused:

Nom nom nom

Buy a new bike

[FJRider]

Rather than paying much attention to the highly questionable/amusing advice being given in this thread you could always stop by the workshop and I can let you know what is wrong with it.

How could anybody turn down an offer like that. I might suggest Grashopper that you PM/contact him soon (if you haven't already) and arrange a suitable time for you both ..

[Coldrider]

our Kat eats grasshoppers

[Grashopper]

Hm, filled the bike up, moved that pipe around and went for a ride, but it was too windy to tell if the bike was still doing that or not. Will see how tomorrow goes and then probably best see Katman if the bike is still behaving weirdly.

[ducatilover]

Are you talking about the pipe to the carb?
It needs to sit on the battery box, or airbox in still air. Otherwise you'll make the poor girl run pig rich when it gets pressurised :niceone:

[duckonin]

If he sees Katman he has some brains . Yep c the kat.

[bosslady]

If he sees Katman he has some brains . Yep c the kat.

She... ;) heh

[FJRider]

If he sees Katman he has some brains . Yep c the kat.

Grashopper is a SHE ... :msn-wink:

[clonak]

Couple of things I noted from my GZ, same engine, different carb. When I purchased the bike it was quite jerky, and got worse and worse, thinking the chain was loose went to tighen it. Half the chain was tight, half the chain was loose, and there for naffed. replaced it, and it was fine. Untill the intake manifold (from the carb to the cylander head) apparently cracked (so I have been told by the mechanic that was to lazy to take it off and replace it.....) causing some problems, back firing and some jerky-ness.

Did you not just have an electrical problem recently as well ? Maybe the battery is not fully charged, the charging unit isnt the best in these smalls engines, so maybe cant handle with a half drained battery. I noticed a mild difference when I put a new battery in the GZ. Also run some carb cleaner through the fuel. On a GZ forum I am on, its the number one diagnoses and usualy fixes most of the problems.

[Grashopper]

Are you talking about the pipe to the carb?
It needs to sit on the battery box, or airbox in still air. Otherwise you'll make the poor girl run pig rich when it gets pressurised :niceone:
Good thought. I'm pretty sure it was the little battery overflow pipe. Didn't know there were more of those open pipes around though. Better check tomorrow.

[Grashopper]

@clonak
The battery thing makes sense. Will check that and keep the other things in mind. Carb cleaner is probably a good idea anyway. Will look that up. Many thanks

[ducatilover]

The battery box vent will have no effect whatsoever on the performance

The manifold could be split, unlikely on one that new though. There is a rubber o-ring on the manifold-to-head surface that can shit out... a cheeky bit of sealant will sort it

[skippa1]

C When I purchased the bike it was quite jerky, and got worse and worse, thinking the chain was loose went to tighen it. Half the chain was tight, half the chain was loose, and there for naffed. replaced it, and it was fine. .

aaaayyyyyeeee?????:confused: dont tell me....the top of the chain was tight and the bottom was loose?

[clonak]

aaaayyyyyeeee?????:confused: dont tell me....the top of the chain was tight and the bottom was loose?

No. I tighened the chain, which must have been at the loose half, and when I tried to move the wheel, it got alot tighter, so I loosened it off, then moved the wheel and it was waay to loose, done this a coulpe of times, and realised what was happening. Half had stretched to much, the other half had not stretched. Dont ask me how it works, because I was confused as hell as well. Was the first chain i had done on a motorbike.

[Grashopper]

Thanks again to Katman for sorting out my bike. He took it for a test ride and didn't actually notice anything wrong with it. Quite a relief, cause I was a wee bit worried. He also checked the chain which seems to be ok and adjusted the fuel/air mix to have run a bit richer. Seemed to have helped but I haven't managed to get on the bike for too long yet today.

[bosslady]

Thanks again to Katman for sorting out my bike. He took it for a test ride and didn't actually notice anything wrong with it. Quite a relief, cause I was a wee bit worried. He also checked the chain which seems to be ok and adjusted the fuel/air mix to have run a bit richer. Seemed to have helped but I haven't managed to get on the bike for too long yet today.

+1 to Katman, good on ya mate.

Grashopper, you may have worried about what appeared to be nothing but the relief in knowing it's ok is so worth it esp to a newbies confidence.

[craigdek]

No. I tighened the chain, which must have been at the loose half, and when I tried to move the wheel, it got alot tighter, so I loosened it off, then moved the wheel and it was waay to loose, done this a coulpe of times, and realised what was happening. Half had stretched to much, the other half had not stretched. Dont ask me how it works, because I was confused as hell as well. Was the first chain i had done on a motorbike.


Sounds like a Chain with seized links. Got dry and was standing so gravity stretched it. Had that on an old off road bike. Threw away that chain. Part of it was good for wrapping around your fist to smash taxi windows when they pulled a 9mm in SA lol.

[Grashopper]

Here an update on the jerky bike issue. We checked the frontsprocket the other day. Turns out it had two teeth less than GNs usually have. Upgraded to one tooth more and voila suddenly I have a much smoother running bike which doesn't feel like it's dying at 100 kmh anymore.:woohoo:

[FJRider]

Here an update on the jerky bike issue. We checked the frontsprocket the other day. Turns out it had two teeth less than GNs usually have. Upgraded to one tooth more and voila suddenly I have a much smoother running bike which doesn't feel like it's dying at 100 kmh anymore.:woohoo:

That would effectively gear the bike up. (ie: Go faster) ... Two extra teeth on the front cog is quite a bit.

[haydes55]

What about the rear sprocket? Is that standard? More teeth on the front or less on the back will increase top end. Opposite will increase acceleration.

[bosslady]

What about the rear sprocket? Is that standard? More teeth on the front or less on the back will increase top end. Opposite will increase acceleration.

Its got 41, so normal

[doc]

Thanks again to Katman for sorting out my bike.

:eek5:
Is he doing freebies ?