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Old July 15th, 2013, 07:22 AM   #1
Crriiissss
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Slow throttle response and slow return to idle help

My friend bought a 2006 Ninja 250 with about 2500 miles in it for $700. The previous owner mentioned it needed a new battery and she doesn't know why it's not starting (so my friend bought it since we could probably fix it up). Initially, it wouldn't turn on after the previous owner had it sitting all winter. We put in a new battery, added some gas and with that, it turned on only with full choke but would die a couple of seconds later. So we went in and cleaned the carbs (sort of). We opened up the carbs, but only cleaned out the pilot and needle jet since we were in a rush to just clean the same parts my friend cleaned on his hyosung 250's carbs to get it running. We put it back all together, with new gas and oil. It starts normally now with no choke but when we twist the throttle, the response is delayed and slow return to idle (about 6 seconds from 5k-6k rpm). We also removed the idle mixture caps and adjusted the idle mixture but it didn't make the return to idle any faster, if anything it made the throttle response even slower.

We know the idle mixture should be about 2 1/2 turns out but how do we go about adjusting both of them? ( turn one side a bit and turn the other side the same amount and than twist the throttle to see how its affected? or turn one side and twist throttle to see how it is before turning the other idle mixture?) We found the site telling us how to adjust the idle mixture but they weren't that specific.

Should we go and clean the carbs again but completely this time? like this http://faq.ninja250.org/wiki/Cleaning_the_carbs_2.

Are there any other possible reasons why it's doing this? maybe spark plugs or anything?

It also looks like the owner left it outside all winter in NJ since there's a good amount of rust on the exhaust pipes under the bike and some on several other areas.

Thanks in advance!
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Old July 15th, 2013, 07:33 AM   #2
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Check for a vacuum leak around the boots between the carb and head. You can spray some WD-40 or similar fluid around the area and listen for a change in RPMs.

Also look at the routing of the throttle cables, and confirm that the throttle snaps shut when you open the throttle (engine off) and let it go.

I would completely drain the gas and add 1 oz per gal of a strong fuel system cleaner like Techron Concentrate to a fresh tank of 87 octane Ethanol-free gas (if you can get it).
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Old July 15th, 2013, 07:47 AM   #3
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Quote:
Originally Posted by jkv45 View Post
Check for a vacuum leak around the boots between the carb and head. You can spray some WD-40 or similar fluid around the area and listen for a change in RPMs.

Also look at the routing of the throttle cables, and confirm that the throttle snaps shut when you open the throttle (engine off) and let it go.

I would completely drain the gas and add 1 oz per gal of a strong fuel system cleaner like Techron Concentrate to a fresh tank of 87 octane Ethanol-free gas (if you can get it).
Will try all 3 sometime this week, thanks!
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Old July 15th, 2013, 08:21 AM   #4
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Vacuum leak is what immediately came to mind. For that, follow above advice.

I'd take off those carbs and clean them thoroughly again though. I'd probably also get the K&L rebuild kits while you're at it. While the bike isn't THAT old, sitting tends to muck things up. If you have access to some sort of compressed air, blow that through the jets every way possible after manually cleaning.
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Old July 15th, 2013, 08:34 AM   #5
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Quote:
Originally Posted by jkv45 View Post
Check for a vacuum leak around the boots between the carb and head. You can spray some WD-40 or similar fluid around the area and listen for a change in RPMs.
Quote:
Originally Posted by Solunatic View Post
Vacuum leak is what immediately came to mind. For that, follow above advice.

I'd take off those carbs and clean them thoroughly again though. I'd probably also get the K&L rebuild kits while you're at it. While the bike isn't THAT old, sitting tends to muck things up. If you have access to some sort of compressed air, blow that through the jets every way possible after manually cleaning.
Alright so I should just spray WD-40 on the boots while idle on neutral and see if it acts the same after blipping the throttle?

I'll look into the K&L rebuild kits, thanks.
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Old July 15th, 2013, 09:08 AM   #6
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Start the bike and let it idle. Just spraying some carb cleaner around the boots and other vac lines will raise the idle or cause the engine to race. No need to blip or anything. In fact, blipping and such my hide a leak further.

Before you buy anything clean the carbs, check the air filter, air box and snorkle area.
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Old July 15th, 2013, 09:36 AM   #7
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Originally Posted by Crriiissss View Post
Alright so I should just spray WD-40 on the boots while idle on neutral and see if it acts the same after blipping the throttle?.
You are just looking for a change in the idle speed that would confirm a leak.

Carb cleaner works too, but it may dull the engine/case paint if you use a lot of it.
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Old July 15th, 2013, 11:53 AM   #8
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Before you buy anything clean the carbs, check the air filter, air box and snorkle area.
This. I'm anal about replacing gaskets and such, but it probably doesn't need it. I would definitely check everything else obvious before buying the kits.
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Old July 15th, 2013, 12:05 PM   #9
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This. I'm anal about replacing gaskets and such, but it probably doesn't need it. I would definitely check everything else obvious before buying the kits.
Will do. Thanks.
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Old July 15th, 2013, 06:50 PM   #10
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I sprayed some carb cleaner on the boots between the carbs and the head and the rpm remained steady. So I guess there's no holes there and I will go with cleaning the carbs again this week.

I also forgot to mention that it takes a while to warm the bike up, or maybe it's just me. It needs full choke to start but it can be decreased completely thereafter. For about 15 mins, a small twist of the throttle turns the bike off. It takes a while longer before twisting throttle actually slowly increases the rpm and than back to the slow return to idle.

I also noticed that with the idle adjustment screw fully tightened to the highest idle setting, the bike idles at about 1.2k rpm, which I know isn't normal.

Any suggestions?

Last futzed with by Crriiissss; July 16th, 2013 at 04:31 AM.
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Old July 15th, 2013, 07:13 PM   #11
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Make sure you spray at EVERY connection. Everywhere you see a black tube, spray near both ends of it. Make sure you check the airbox-carb boots as well. Also, spray around the choke plunger and the throttle butterfly.

As long as this turns up nothing, I think it's time to tear down the carbs and clean the crap out of them.

...Why did you bump your idle up to 12k?? lol
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Old July 16th, 2013, 04:30 AM   #12
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Quote:
Originally Posted by Solunatic View Post
Make sure you spray at EVERY connection. Everywhere you see a black tube, spray near both ends of it. Make sure you check the airbox-carb boots as well. Also, spray around the choke plunger and the throttle butterfly.

As long as this turns up nothing, I think it's time to tear down the carbs and clean the crap out of them.

...Why did you bump your idle up to 12k?? lol
Ooo alright...I'll go do that when I get the chance...I meant 1.2k lol
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Old July 16th, 2013, 05:54 AM   #13
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....Any suggestions?
Carbs still dirty.

https://www.youtube.com/watch?v=0U3a_FtDSqg
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Old July 23rd, 2013, 03:10 PM   #14
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My friend cleaned the carbs as it's supposed to be done, sprayed around hoses but no change in idle. Here's a video, same as before.

http://www.youtube.com/watch?v=lAx17iNRyPA
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Old July 23rd, 2013, 05:06 PM   #15
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My friend also noticed that sometimes when the bike is on idle, there's a hiccup where the rpm jumps and than drops down. You can see it in the following video.

http://www.youtube.com/watch?v=2zAQSomMNqU

Any thoughts anyone?
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Old July 24th, 2013, 08:28 AM   #16
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Quote:
Originally Posted by Crriiissss View Post
My friend also noticed that sometimes when the bike is on idle, there's a hiccup where the rpm jumps and than drops down. You can see it in the following video.

http://www.youtube.com/watch?v=2zAQSomMNqU

Any thoughts anyone?
Did you remove the idle mixture screw caps? Chances are the mixture could be adjusted.

Were the jets and jet holder removed and cleaned carefully? They need to have a small copper wire inserted and the jet spun around it to remove deposits on the inside of the opening. I've seen jets that you can see light through, but even after repeated spraying with carb cleaner were not completely open. Using the copper wire and carb cleaner will open them up. The jet holder can also be crushed down if tightened too much.

You shouldn't need full choke for any length of time to keep it running. There is a blockage of some kind in the carb.
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Old July 24th, 2013, 08:32 AM   #17
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Did you remove the idle mixture screw caps? Chances are the mixture could be adjusted.
Yup. I think they're both 2.5 turns out.
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Old July 24th, 2013, 08:49 AM   #18
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it's either dirty carbs, unsynced carbs or vacuum leak. possibly a combo of those three.

dirty carbs can be cleaned, you can do a quick visual on the sync while you have them out so their in the general range. for the vacuum leak, well just inspect both boots on both sides for cracks, etc. maybe it came out from the airbox side.
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Old July 25th, 2013, 08:16 AM   #19
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it's either dirty carbs, unsynced carbs or vacuum leak. possibly a combo of those three.

dirty carbs can be cleaned, you can do a quick visual on the sync while you have them out so their in the general range. for the vacuum leak, well just inspect both boots on both sides for cracks, etc. maybe it came out from the airbox side.
I hope you're right. Already cleaned the carbs (twice, maybe a third time if I'm free this weekend using copper wires), no vacuum leak that we can find, and I just made the instrument to sync the carbs and check it later on this week.

Is that all that can be causing the slow throttle response along with the slow return to idle?
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Old July 26th, 2013, 08:13 AM   #20
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Either the slow/pilot jet is still clogged or it's out of sync. Also might want to check your air filter to see if anything has made a home out of it.
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Old July 31st, 2013, 12:31 AM   #21
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i had this problem just last month. pulled the carbs since the vac leak check didnt find anything. found i had routed the vac lines wrong between the small and bigger lines. as soon as i swapped them with fresh vac lines it now purrs like a kitten and roars as loud as a 250 can roar. lubed the throttle cable and now its very responsive.
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Old July 31st, 2013, 05:08 AM   #22
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i had this problem just last month. pulled the carbs since the vac leak check didnt find anything. found i had routed the vac lines wrong between the small and bigger lines. as soon as i swapped them with fresh vac lines it now purrs like a kitten and roars as loud as a 250 can roar. lubed the throttle cable and now its very responsive.
Which smaller and bigger lines?
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Old August 7th, 2013, 12:26 AM   #23
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Which smaller and bigger lines?
you have two lines that go between the carbs. one is larger then the other and one that bridges the two carbs. i had both the smaller and larger lines flopped that goes between the carbs but also frogged the two larger lines that bridged the two carbs.
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