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/sh...le-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.

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)

[haydes55]

Jerky bike

And here I was expecting a bike made out of jerky

[Haggis2]

And here I was expecting a bike made out of jerky

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.