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hey OP, the translucent brown hose is linking both carb vent fittings together? An immediate issue right there, no matter what the application. Each vent should be open to atmosphere.
You've been inside the bowls? Did you happen to examine and document the main and pilot jet sizes? (stamped by number)
Ditto on the needle? Number on the side?
 

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Discussion Starter #22
Both translucent hose are free and not connected. First try after examining the choke jets by the compressed air. Tomorrow I will check numbers on the jets. I wonder most why the suction slowly stopped working. Today, there was also no reaction to the choke when firing, but as I warmed up the engine, pulling the choke and adding gas made the engine stay at 4k revolutions after releasing the gas.
 

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Another thing I see missing is the choke cable bracket that is held on by the top carb cap screw. If I'm not mistaken the carbs for the 94 should be the same as an 05, and if that little bracket is missing the choke won't work at all. It was missing off of mine when I bought it. Kawasaki part #11045-1824, but personally I made one with some scrap steel piece I had laying around, $55 for a piece of steel less than an ounce is a bit ridiculous.

Funny enough I found out a little while ago that my carbs are from ducatiman, the previous owner sent his out to custom carb services llc, then when he got them back decided he didn't want the bike anymore lol.
 

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ok. something is not right here. where are the original carbs. those carbs are not suitable for the GPZ500s they are meant to be on a different type of bike on the the bike they come from those brown pipes ducatiman was on about connect to a device that does something in the Emission Control circuit. the whole set up is wrong. you will find this out when you post the sizes of the jets and needles.
meanwhile you originally said these carbs were fitted by a PO to reduce the power output. and now by a mechanic while you were away. someone has the proper carbs for this bike somewhere.
 

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A pic in post #8 the choke cable bracket clearly visible. One of you pics led me to believe the vent hoses were connected together. Your individual vents completely differ from EX500 common rail. And notice the fuel rail is flipped sides from EX500 as well....again, usable but different.
Never any doubt, no argument different configuration Keihins from another model.

OP I'm surprised in cleaning them, you didn't note jet sizes already, an important little detail.

So @yorkie what other Euro 500 models exist? Here in US we have the Vulcan cruiser ( used 2 differing carbsets depending on vintage)
What variants you got over there?
 

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what using similar carb setup. GPZ500s. ER500. ER5. EN500. EN450 EN454 KLE500 KLE500x and that is just the carbs sets that theoretically will bolt straight on. others use same carbs but vary the spacing between them. like Yamaha XS range 250 to 650.
 

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Discussion Starter #28 (Edited)
@yorkie to increase the power. They said taht the oryginal carbs are sold. @ducatiman Yes, I don't think about measurement. When I go back to my computer i have read Your message about the size of the jets
It just occurred to me… What about fueling a cold engine? If the fuel tap does not open fully on a cold engine (e.g. vacuum too low or hose too soft and go flattening? Works well when the engine is warm and the vacuum is too weak, when the engine is cold, and the bike is not getting the right amount of fuel with the choke on?
 

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the bike is not getting the right amount of fuel with the choke on?
that is the only thing in the last post that makes any sense.
either your not listening to what you have been told or do not understand. you are saying you have a choke problem when I believe the whole set up is the problem not the choke until you return the bike to the original stock specification (without modifications) the problems will persist.

I could try to explain why but I think it's pointless. I am just about done here until you have new information on what the set up is.

in brief you have a bike that someone restricted to so he could ride it on a learner licence. you got it and some dumb mechanic thought that fitting a set of carbs from a different bike was the answer instead of unrestricting the ones on the bike. It did not work did it and that is because the carbs he fitted were from a bike that has restricted power already.
the whole setup is wrong for this bike. end of story.
 

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beyond carbs, have airbox intakes been restricted as well? Other functions may have been played with too. Unknowns.

It is within the realm of possibility to convert the carbset back to EX500 needs, however, 2 or 3 fixed tuning areas would require critical, precise measurement/comparison to EX spec, and possible modification. No doubt easier, more efficient to source correct from a breaker. Agree with @yorkie at this point best for OP to find a correct set. Beyond....replace the petcock, verify integrity of entire air/fuel intake system. Valve clearance check, sparks, wire service..the whole complete tuning overview game.
 

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hi. Duc. I think we are on the same page here. but for information only. you know the carb set specs of the EX better than I. so that can be left said. the carb set he has is from either a ER500 or the later ER5 with all the trimmings.
I suspect the ER500. the carbs are lower spec than the EX in a few ways. the cabs flow rate is lower typically around 32CFM the EX is 37CFM. the jets are smaller different needles and most of the internals are a different size. the airbox is also smaller and the lift hole in the slides is smaller 2mm instead of 3mm. the springs are lighter as well.
this set up is for a bike with a power output of around 35/40 bhp. with milder cams and lower compression ratio.
is this going to run right on a EX I doubt it.

for Gregory. they have done you no favours changing the carbs my friend. I have seen this before. on the old UK forum a guy from Holland bought a GPZ500s from a learner rider that had been restricted. he wanted to de-restrict it and put it back to full power.
it took a few attempts but we found them all one by one and he got the power back. to un-restrict them you take out the 30mm diameter washers from the engine side of the carb inlet rubbers. remove the restrictor plate from the airbox air filter housing. then remove the tamper proof throttle plate movement device. reset the carbs. that's it full power.

side note these mods have to be done at an approved transport department so a certificate can be issued to prove the bike is restricted and comply with the regulations for learner rides. but you do not need a certificate to return them to full power just take them off. it could have been so easy now it's not.
 

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Discussion Starter #32 (Edited)
@yorkie Probably my bad english caused some misunderstanding. I have already bought the bike with increased power. I didn't do anything about it. I don't need a sportbike. It's only GPZ. I bought this motorcycle (as I wrote) a few weeks ago, I did a post purchase inspection: oil, filters, spark plugs, drive, tires, etc. and drove about 2500 km. Everything was fine. After this time, the choke was getting worse and that is why the motorcycle went to a mechanic and this is my reason for visit to the forum. Choke works fine thrue 2500 km
@ducatiman all jets are as You describes 130 main, 35 pilot jet,
N36N needles? - i don't know how to check it
 

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pulling the choke and adding gas made the engine stay at 4k revolutions after releasing the gas.
This is a sign of a vacuum leak, if the carb boots are old, that it probably where the leak is. From everything else you've described and everyone else has commented on, you have to:

1-Get the correct carbs for the bike, its painfully obvious the ones you currently have are incorrect for your bike.
2-Confirm all other maintenance is up to date, valve clearance, wire service, etc such as ducatiman has stated.
3-Confirm vacuum leak, considering the age of the bike it wouldn't be a bad idea to replace the carb boots and vacuum lines, especially if they are hard and/or brittle.

Until these are done, there's really not much more we can help you with.

And just because they worked when you got the bike, doesn't mean they were working how they should have.
 

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@yorkie yes, but they worked. What may be wrong now? That's is the question. PLS don't be annoyed.
I'm not annoyed or upset in anyway don't think that it's not my nature. call it frustration. a bit like playing a game where the rules change every hand. it is hard to keep up.

I little story just for you. I have two GPZ's one an old gen 1. and another gen 2 I built myself completely out of spare parts. while building the gen 2 I bought a box of spare parts from a autojumble inside the box was a pair of carbs just like yours but from a EN450 with chrome tops.
great news I stripped them down cleaned them and replaced all the internal parts with OEM bits. put them on the bike and it ran great nice and smooth really pleased. the only issue was the choke it sort of only half worked. that and it always seemed to run rich at low revs. I put that down to a choke issue.
during the next winter I rebuild the gen 1. so while it was in pieces I borrowed the stock carbs from it and put them on the GEN 2. WOW all the issues were gone. and it ran 80% better than it ever did.
they are still on that bike today. the GEN1 got rebuild with another set of stock carbs. I still have those EN carbs they are in the spares box where they belong.
 

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Discussion Starter #37
Hi. After a month but for everybody who has problem with choke. Not only carburators. Valves was adjusted not properelly. Suction valves has got no freeplay. After adjustment: everythings works fine and choke works as it should. Gregor
 

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Good that everything works fine (y)

What do you mean with "suction valve"?

My GPZ500 is running with ER5 carbs with the original GPZ jetting and needle. It is running fine with good power output, so it is possible ;)
 

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Good that everything works fine (y)

What do you mean with "suction valve"?

My GPZ500 is running with ER5 carbs with the original GPZ jetting and needle. It is running fine with good power output, so it is possible ;)
hi. he means the inlet valves. English is not his first language not to matter suck valves and blow valves is descriptive enough. and yes there is far more to effective running than what you may believe the issue to be.
glad yours is running ok as they say in engineering everything is possible. as long as you are happy with the set up great. it is not perfect of course but as long as your happy.
 

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In all fairness, my bike has been on a Dyno recently and it turned out to run even better with a slightly more tapered needle and a slightly bigger vacuüm hole in the slide.

To know for sure that the bike runs even better with a set of original carbs, I would have to buy a perfect set and put it on the Dyno again. I'll have to ask for a raise first... 😉
 
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