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Old 02-23-2015, 11:18 AM   #1
ieathonda
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Jetting/Needle height adjustment question ninja ex250

Ive got a ninja ex250 2005 that i bought a few weeks ago. Has a muzzy slip on exhaust. Did an airbox mod a few days ago and thought i should be good with a few #4 shims under the needle. Well im at 4 shims now and mid range still is lacking. I will be ordering a factory pro jet kit with adjustable needles sometime this week but wanted to see if I could get a few answers before it comes in.

Idles great. blipping the throttle, the rpm's climb and drop instantly, no hang or hiccup of any sort.

at WOT from first gear, accelerates hard until about 4k rpm. 4k rpm - 8k rpm feels like ive hit a wall. It just steadily climbs until about 8k rpm and the bike comes to life and shoots off. Having the throttle half open through the 4k-8k rpm range feels as if it has better acceleration than WOT.

After 8k rpm the bike pulls hard to redline with no issues.

Im unsure of whether it is running lean or rich, seems a little bit hard to tell since ive never worked on carbs before. I will pull the plugs soon and try to get a better reading that way.

In your own opinion, what do you feel is causing the mid range stumble that im getting? its taking most of the fun out or accelerating
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Old 02-23-2015, 02:26 PM   #2
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It's a 250, so mid range is gonna suck, but you're more than likely running lean. Was it jetted properly after the Muzzy? Factory Pro kits will come with setup instructions, and they'll probably even have a jet/needle recommendation for your exhaust/intake combo. If not, just give them a call. I've dealt with them in the past, and they were very helpful.
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Old 02-23-2015, 02:41 PM   #3
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It's a 250, so mid range is gonna suck, but you're more than likely running lean. Was it jetted properly after the Muzzy? Factory Pro kits will come with setup instructions, and they'll probably even have a jet/needle recommendation for your exhaust/intake combo. If not, just give them a call. I've dealt with them in the past, and they were very helpful.
It was not jetted at all after the exhaust which i confirmed after cracking open the carbs.

The midrange was not at all sluggish before the intake and only slightly lagged at 5-6k and got over it pretty quick. now, it takes about a full 4-5 seconds to even get through 4-8k and it only steadily climbs at WOT. I will get the kit and see if i can tune it correctly with their adjustable needles
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Old 02-23-2015, 02:51 PM   #4
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I'd be more worried about getting the main and idle jets right. After that, you can fine tune with the needles. Needles won't mean a thing if your main jets are too small.
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Old 02-23-2015, 04:36 PM   #5
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Thats what I have come to a conclusion of.. I know the 250's come pretty lean from the factory as is due to EPA emissions. I will be getting the FP kit and go from there. hopefully it takes less than a dozen times to get the jetting right.
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Old 02-23-2015, 06:18 PM   #6
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Don't get hung up on that "lean from the factory." That's just talking about the pilot screw adjustment so it's a little lean at idle. Once you hit the throttle, that goes away, and it's common on all carbed bikes. You'll probably have to drill out the plugs that cover the pilot screws so you can adjust them after re-jetting.

If the instructions come with jetting for a Muzzy + K&N, it'll get you close. If it was me, I'd be calling FP now and writing down their recommendations instead of waiting for the kit to come in. For me, they were dead on with the jets, but their needle recommendation was off by one position. Whatever you do, do not separate your carbs. Leave them connected so you don't have to worry (as much) about getting them sync'd. Just do a bench sync while they're off and you'll be fine. I vacuum sync'd my cruiser once, and it didn't offer a bit of noticeable improvement over a bench sync.
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Old 02-23-2015, 08:22 PM   #7
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Don't get hung up on that "lean from the factory." That's just talking about the pilot screw adjustment so it's a little lean at idle. Once you hit the throttle, that goes away, and it's common on all carbed bikes. You'll probably have to drill out the plugs that cover the pilot screws so you can adjust them after re-jetting.

If the instructions come with jetting for a Muzzy + K&N, it'll get you close. If it was me, I'd be calling FP now and writing down their recommendations instead of waiting for the kit to come in. For me, they were dead on with the jets, but their needle recommendation was off by one position. Whatever you do, do not separate your carbs. Leave them connected so you don't have to worry (as much) about getting them sync'd. Just do a bench sync while they're off and you'll be fine. I vacuum sync'd my cruiser once, and it didn't offer a bit of noticeable improvement over a bench sync.
I was going to go ahead and pull out those plugs the next time I worked on the bike since itll probably be one of the things I need to mess with after the jetting.

I was also going to do a valve lash adjustment and sync the carbs after. The bike only has 11k miles, not sure if that's enough mileage to impose a tune up (never owned a bike before) but I will double check anyways.

I did see a few different ways to sync but ill try both. Ill give FP a call tomorrow and see what they have to say about a set up thatll work for me. thanks for your help thus far
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Old 02-23-2015, 09:37 PM   #8
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if you did an air box mod and it has exhaust your are definitely running lean with stock jets. Id take it easy until you get the jet kit in. Hauling with a lean condition is a recipe for disaster.
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Old 02-24-2015, 12:04 PM   #9
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Quote:
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I was also going to do a valve lash adjustment and sync the carbs after. The bike only has 11k miles, not sure if that's enough mileage to impose a tune up (never owned a bike before) but I will double check anyways.
More than enough miles for a tuneup, since you never know how well the previous owner took care of it. Valve checks for the 250 are recommended every 6k miles. Pretty simple to do, but a bit time consuming if it's your first go at it. Don't forget to replace the o-rings on the coolant tubes. They're a weird size (13.8 x 2.4 mm, or something like that), but you can find them in the metric o-ring kit from Harbor Freight (~$7). You can get them from cheapcycleparts, bike bandit, Ron Ayers, etc, but shipping will be the same or more than the HF box.
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Old 03-31-2015, 03:00 PM   #10
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update... bike pulls hard through the rpm range. 100x better than it was before i tuned everything.

did valve lash clearance, tuned/sync'd the carbs with a factory pro kit and shimmed the needles, installed K&N filter. lubed cables and chain and other maintenance doodads.

ended up running a 112 main and 2 3/4 turns out on the mixture screw with 4 shims in between two circlips on the factory pro needle.
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