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Old August 16th, 2018, 03:42 PM   #1
bosozoku
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slow return to idle - really could use some help

Hello everyone, new member here that has an erratic running 1997 Ninja 250R with 1000 miles on it (last running 2007). It's exhibiting crazy carburation problems of erratic return to idle, increases to high RPM's (5000) on its own with choke off (verified closed), doesn't come back to idle when throttle is opened and closed, takes forever to do so if it does at all.

The carbs were removed, disassembled and cleaned including the pilot air-screws. Diaphragms, slides and needles looked fine. We replaced the main & pilot jets with new jet. Float valve on one side that looked suspicious was also replaced. Enrichment valve was not disassembled. Fuel flows into carbs normally but petcock vacuum diaphragm seems stuck open. Planning to replace with non-vacuum petcock.

We then cleaned and swapped carbs from another 1996 Ninja 250R (also last running 2007). It is still exhibiting the same slow return to idle. We checked for any vacuum line leaks, everything seems fine.

Do any of you have any suggestions what could be causing this!? My father and I would greatly appreciate your help...Kind regards Jesse
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Old August 16th, 2018, 04:58 PM   #2
jkv45
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I know you said you checked for vacuum leaks, but that's what it sounds like to me.

There's also a huge grey area when someone says they "cleaned the carbs", so that's always suspect. If the other set of carbs wasn't proven to be good, and sat for the same amount of time, swapping them may not isolate the problem. Have you confirmed the slides rise and fall smoothly and evenly, and sit down all the way. Are the Needle Jets in place? Did you bench sync the carbs? Did you clean the idle mixture passages, check the o-rings, and set the screws to 2.5 turns out as a base?

If the choke (enricher) in hanging up it might cause something like you described.

As far as a manual petcock goes, we put one on one of our Ninjas - and it was a pain. The lever sits up too far under the tank and was very difficult to turn on and off.
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Old August 16th, 2018, 07:56 PM   #3
bosozoku
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Thanks for the input! We’ll keep looking for vacuum leaks.

Yeah the other set of carbs may have the same or similar issue from sitting. We didn’t remove the pilot screws on the one carb. And the other one, which we did remove the screws from, seems to have been factory set at 1-5/8 rather than 2.5 – but we tried both settings – should be set around 2.5 turns out currently. The slides rise and fall smoothly and evenly. Pretty sure they sit down all the way but that’s something we can double check. Needle jets are in place. We didn’t bench sync the carbs – we left the carb sync as it was. Regarding the idle mixture passages, we shot carb cleaner down the pilot jet tube and confirmed it would come out in the venturi. Are there additional mixture passages to focus attention on? We didn’t remove the o-rings, but that is something we could look at. Is it just the o-ring in the pilot screw hole you are referring to? Or are there other o-rings to look at?

Just took the cover off the enricher, didn't see anything of interest there. Air cut off valve diaphragm looks fine. Were you referring to the actual choke - that we might want to look at that?

Thanks for the heads up on the petcock – I could see how that might be a pain.

Last futzed with by bosozoku; August 16th, 2018 at 09:57 PM.
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Old August 16th, 2018, 10:09 PM   #4
CaliGrrl
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Welcome, and good luck. Carburetor problems will drive you crazy. With my husband's bike, we had to find a carb expert and have *him* clean the thing, and then we had to replace the fuel line because it was completely blocked from sitting too long.
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Old August 17th, 2018, 06:54 AM   #5
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Quote:
Originally Posted by bosozoku View Post
Thanks for the input! We’ll keep looking for vacuum leaks.

Yeah the other set of carbs may have the same or similar issue from sitting. We didn’t remove the pilot screws on the one carb. And the other one, which we did remove the screws from, seems to have been factory set at 1-5/8 rather than 2.5 – but we tried both settings – should be set around 2.5 turns out currently. The slides rise and fall smoothly and evenly. Pretty sure they sit down all the way but that’s something we can double check. Needle jets are in place. We didn’t bench sync the carbs – we left the carb sync as it was. Regarding the idle mixture passages, we shot carb cleaner down the pilot jet tube and confirmed it would come out in the venturi. Are there additional mixture passages to focus attention on? We didn’t remove the o-rings, but that is something we could look at. Is it just the o-ring in the pilot screw hole you are referring to? Or are there other o-rings to look at?

Just took the cover off the enricher, didn't see anything of interest there. Air cut off valve diaphragm looks fine. Were you referring to the actual choke - that we might want to look at that?

Thanks for the heads up on the petcock – I could see how that might be a pain.
This section has a lot of info that may be helpful - https://faq.ninja250.org/wiki/Intake

After removing the idle mixture screws, and confirming the o-rings are good and in place, you need to check that the passages are open. The o-rings sit on the screws, above the spring and washer (o-rings closest to the carb).

2.5 turns out on the idle mixture screws is a good place to start. Original adjustments vary, but are always on the lean (in) side.

Bench syncing the carbs is just a good starting point. Checking with a vacuum gauge later, when it's running well, should show it to be very close. If it's not there may be other issues (valve adjustment, vacuum leak, etc).
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Old August 17th, 2018, 09:28 AM   #6
bosozoku
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Thanks -- wondering if the old hoses may have a leak we can't see or leaky connection at one of the barbs.

We opened the enricher again, pulled the diaphragm, and polished the brass post as it had some tarnish. Hoping this may help in the operation of the air cut valve. Rubber seemed fine. Surprising how much spring pressure there is in the enricher.

Last futzed with by bosozoku; August 17th, 2018 at 11:04 AM.
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Old August 17th, 2018, 12:31 PM   #7
Ceeloo Yello
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They do sell aftermarket rebuild kits for the petcock. I just got one off of ebay for around $25 with free shipping.
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Old August 18th, 2018, 06:40 PM   #8
bosozoku
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I thought the petcock rebuild kits were more expensive - good to know. Took the petcock apart today and cleaned up the rubber washer that seals off the fuel. And also cleaned the metal on the mating surface -- looks like it should be more apt to seal now. Diaphragm seemed in decent shape. We tried a "Raptor 660" petcock that was supposed to be a non-vacuum replacement but valve was way too close to the tank so gave up on that petcock.

Checked the enricher on the other carb and looked fine -- no tarnish on the brass post, and rubber diaphragm looked fine.

Checked the airbox and - boy oh boy - what a disaster! After 20+ years, the oiled foam was totally disintegrating, really nasty. Hoping we could be onto something, potentially was blocking air flow. Didn't look like the foam bits made it into the carb fortunately. Ordered up a new air filter so will give that a try next, now that we know the enricher looks fine.
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Old August 22nd, 2018, 04:52 PM   #9
Nextbesthing
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Quote:
Originally Posted by bosozoku View Post
I thought the petcock rebuild kits were more expensive - good to know. Took the petcock apart today and cleaned up the rubber washer that seals off the fuel. And also cleaned the metal on the mating surface -- looks like it should be more apt to seal now. Diaphragm seemed in decent shape. We tried a "Raptor 660" petcock that was supposed to be a non-vacuum replacement but valve was way too close to the tank so gave up on that petcock.

Checked the enricher on the other carb and looked fine -- no tarnish on the brass post, and rubber diaphragm looked fine.

Checked the airbox and - boy oh boy - what a disaster! After 20+ years, the oiled foam was totally disintegrating, really nasty. Hoping we could be onto something, potentially was blocking air flow. Didn't look like the foam bits made it into the carb fortunately. Ordered up a new air filter so will give that a try next, now that we know the enricher looks fine.
I just bought a 9 dollar china replacement petcock for shits and gigs. I'll let you know when it comes how she works.
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