Kawasaki Sportsbike Riders Club - Australia - Online Forum

Hey guys bought a GPX 250 abotu 2 months ago, and am having some problems with it. Heres the story...

For people who dont want to sift through this wall of text, just read the the last paragraph or two

It's a 1990 GPX 250 (Black/red), bought it for $1300. It had a small fuel leak, which I knew about, and bought the bike regardless. I rode it from Coogee (south syd) to Newcastle only stopping to fill up. No problems with the bike at all. I was staying in Newcastle at the time, so I got my dad to come pick the bike up from Newcastle and take it home for me (coffs).

When I got home from my holidays, we ripped the tank off the bike, and found the dource of the fuel leak. It was underneath the tank, where the tank sits on the rubber grommits on the bike frame. The ex-ex owner obviously knew about it, and tried to bog it up somehow, which obviously failed over time. Anyways, we drained the tank, cleaned it out, and one of dad's work mates offered to weld it. He did a perfect job, excellent welder.

So the tanks back on, but the tap is clogged up with crap from cleaning it out. We took the tap apart and cleaned it out, noticing that the fuel filters are f@#^ed.

cleaned the tap, and started up the bike with a small amount of trouble. We got it to idle with difficulty. and noticed that there we smoke coming from the headers. I took them off, and they are pretty much made of rust. So I bought some new ones, and replaced them. Started the bike up again, and it still wasnt idling properly, just preffering to die.

I noticed the throttle was sticking, then realized I was wrong and the cable was actually snapped. So I replaced both cables, and all is good there.

Sow we took the bike apart the other day, cleaned out the carbies, one bowl had a fair amount of crap in it, other one did as well, but not as bad. We put everything back together, cleaned out the fuel tank as best as we could, bought a new filter, and started back up again with fresh fuel. Still wont idle properly, with or without choke.

The throttle response is really weird. Rev's will change whilst keeping the throttle still, and if i am to let the revs get too low, and try to give it a bit more throttle to keep them up, the response is 2 or so seconds late.

We've tried fiddling with idle speed, which didnt help at all cause the revs are so unstable. Fuel tap is fine, fuel is coming out clean and at the right rate. Any ideas? I really need to sort this out ASAP, so any help/ideas are appreciated!

With the carb clean did you remove inspect & clean the jets etc & use compressed air to blow out any blockages? what position is the choke in? did you replace the plugs while you were under there?
So many possibilities

Yes the jets are fine, we cleaned everything out with compressed air, floats are in perfect nick. with or without choke the revs are still weird. dont have a long enough extension to get the spark plugs out, so I'm going to super cheap this arvo to get one to check the plugs. Any other suggestions assuming the plugs are fine?

Coil could be on the way out but does not explain the rise n fall of revs

Is it also a possibilty that something in the carb isnt opening up enough (dont really know that much about carbs n how they work) when the throttle is open? the throttle cable itself is in perfect condition, and is adjusted correctly

The diaphram in the carb that holds the needle, make shore there's no tears and moves freely
That's controlled by the air pressure in the carb.
Also make shore both carb butterflies are allowing the same air in. Get a drill bit and set the both the same.

I use a small drill bit, and place it in one carb, then set the idle screw to that opening (sometimes a spacer or somethings needed) and adjust the other butterfly to suit

Also check the pilot screw setting (usually around the float bowl on the main body. Wind it in till it bottoms out while counting the amount of turns (this is the mixture screw it's important to remember the amount of turns) then remove and clean, do this to both and then set them back.

Usually there around 2-2.5 turns for a standard bike

See how ya go

I just looked then, I can't see a pilot screw? which side is it on, the side with the idle adjuster or the other? Don't have the time to take the carbs apart again at the moment and probably wont for a while.

I've noticed that when we start the bike up after a couple days, we can get it to idle fine first up, but continued attempts at re-starting and getting it to idle just makes it become more and more difficult. But if I leave it for a while again it will idle fine for the first attempt. does that help at all?

OK so I started her up again this morning, can only get it to start with full choke. The first time I started it the revs kept bouncing up and down ~500-1000 revs around 3.5k rpm. The revs were only bouncing on the first start though. Every other start with full choke, the revs stayed even, but if i even slightly closed the choke it would die straight away every time. Any ideas?

*edit* I can start it without the choke and a bit of throttle, but I can't let the throttle go at all. I've tried to adjust the idle speed but It' just wont Idle.

Inlet manifolds cracked or leaking? Sometimes need sealing from manifolds to head. Diaphragm in fuel tap may be torn or have pinhole too.

Fuel tap is definetly fine, I had it replaced. How can I check if the manifolds are cracked/leaking?

Still sounds like crud in either the tank, lines or carbs. I would check the tank to see if it has any loose rust in it, reclean the lines, replace the filters, and redo the carb cleanout just to make sure. None of these things cost you money, just time. Also check that you have your vacuum lines attached as that can cause funny idle issues too.

I can suck on the vacuum line on the fuel tap and fuel gushes out of the tap, and its clean fuel as well, so the tap, tank or fuel isn't the problem. When I take the fuel line off the tank, clean fuel comes out of the carbs as well.

How can I check if the actual vacuum line is working?

I replaced the hose clamps around the manifolds, and bought some spark plugs/plug remover. I'll replace them tomorrow morning 'cause I have to work tonight.

Jimmy37 wrote:Fuel tap is definetly fine, I had it replaced. How can I check if the manifolds are cracked/leaking?

Get it running then spray(drown) the rubbers with WD40 or similar and note any changes to behaviour of the engine- no change no leak.
Remove your spark plugs and inspect for colour, this will tell you your mixture. http://www.theultralightplace.com/sparkplugs.htm

Small carbs have REALLY small air ways in them. My money is on one of the air bleed galleries being restricted. Remove both carbs and soak 3 days in carbie cleaner. Disssemble and clean thoroughly. Preferrably inside. Under a bright light. Dining tables are perfect for this....
In Order,
Take the covers off, double check the throttle cable/s . Are these push/pull cables or one for each carb? Could be out of whack.
Put the fuel tap in the prime position, does fuel pour out of the carbs? If so your needle and seats are shagged and need replacement. This will affect your operating mixture ratio as the fuel height in the carb bowls will br wrong.
Once you are sure the fuel height in the bowl is right, check your carb balance. Google it, or search here. Pretty easy on two cylinders.

Do the above with a manual for guidance and I would be stunned if the bike is not fine.

Thanks a lot for all the advice everyone, much appreciated.
Planning to once again take the carbies out again tomorrow and clean, as well as change the spark plugs. Hopefully all goes well

OK So, I didn't end up taking the carbs out/apart. I replaced the spark plugs, the old ones were petroly and burnt out black. I thought the choke might be playing up so I disconnected the cable from the carbies and voila, hello idle! However, as you know, all good things must come to an end, and it soon started to not idle properly again. I took it for a ride up the street, first gear is quite slow, the bike will splutter in 2nd for a second or so, and then bam, all the power kicks in in third gear, almost like a powerband. rode up and down the street about 700 metres noticing the power drop and spluttering up both ways of the street.

If I'm idling with the clutch in, let the clutch out to drop the revs, and then squeeze the cluth again, the revs wont climb back up, they'll just stay where i dropped em too, It seems that the revs arent dropping as fast as they should be after you rev it.

Anyways, I've now moved to Melbourne since then, and left my Bike in Coffs for a week or so, I am getting it shipped down soon.
Buying a carb kit for it when it gets here, and planning to spend a whole day or two taking it all apart slowly and properly cleaning everything. Is there anyone here in Melbourne that would like to give me a hand or two? I don't have any tools as of yet, and would love some more experienced advice and hands helping me out. Maybe I could throw in a few drinks