"Lil Miss" got cranky and stumbly

[GAU-8]

Hey all. Had a recent issue with one of my ninja's. I''ll call her "lil Miss" for now.

A little background info on her.

2008 Ninja 250: 8k Miles. One accident, after accident, an aftermarket slip on exhaust was installed. From my understanding valves were performed around time of repair. (I do not know if the prior owner, did or did not have a jet kit installed, with the Yoshi slip on)

then she was donated to our school

I do KNOW this.. a few times at the school, she was used, and had a minor flat spot, around 1500 rpm/drive off. but it was minor. like an off idle stumble. One week she is riding great. I come back after the weekend, and apparently she has a HORRIBLE flat spot now. (maybe a student dropped her??) so digging in..basically, giving her gas, between 1000-2000 rpm kills her, until you blip throttle, and get it above 2k. at which point it will climb between 3k to 5k and hang around there for a few seconds.

- One spark plug CR-8HSA, other is CR-8 HA (or something, it was missing one of the letters.) one was a little darker than the other. Replaced both with new CR-8HSA, and gapped per specs. NOTE: this was going by online. Since she is so new to us, we do not have a current '08 manual in our hands yet, but its on the way.

-Airfilter is clean, dry and new.

-carb fuel mixture screws. one is 3 turns out, one is 3-1/2 turns out. (NOTE: since im limited with internet at the shop, I matched both at 3 turns out, before I can research here/now.

pulled the carbs, cleaned out as much as I could, sprayed carb/choke spray through the orifices. no gummy-ness, or noticeable detriments.

Synched the carbs. (after warm up)Using the handy info from here on how to use "T"s for easy synching, without moving the messy hose issues)

: note: One of the boxes near battery, is making an electomechanical "etch etch etch" noise. which seems to coincide, with rpm/stumble, at idle. sometimes random, in a concise series, and/or not at all. (I have a photo of it, but currently on phone. after editing it I will upload.)

As she sits. needs a good 10 minutes to warm up. if the idle is set to around 800-1k , i can slowly ride it off, gingerly, and no stall issues. If I keep it set between 1100/1500 RPM, it will die on ride off. Almost no throttle can be given. also at this range, it will hunt and peck, between 1100/1500 rpm.

if set roughly 1600/2000 rpm. you can drive off, no hangups, but the bike will idle at 3 or 5 k for a few seconds then back down. and damn, that idle adjustment screw is a beast to turn. even after lubricated.

Anyways, thoughts, ideas, and maybe general info on 08 ninjas I may not know yet, characteristic wise.

sorry for length. trying to be concise and thorough, all though I can be wordy!

[rojoracing53]

sounds like dirty carbs specifically the pilot jets. You could try running a tank with seafoam through it to see if you get lucky, but I doubt you'll avoid a full tear down of the carbs. While you have the carbs off triple check everything is the correct size.

[HoneyBadgerRy]

Sound like it needs a carb clean and rebuild.

[allanoue]

I vote, try the seafoam fist. If that does not do it, tear down the cards.

[GAU-8]

READERS DIGEST..... exactly the same outcome. below 1500 rpm dies. above 15/1700 rpm, still climbs to 3 to 5 k, and hangs, then settles to about 2 k.


for those that like to read. scroll below.

Did a complete disassemble (again), removed all jets, needles, diaphragms, screws.( anything that could come out, CAME OUT) Let it sit in carb cleaning fluid for an hour, then sprayed all orifices, springs, screws, tubes with a carb cleaner spray. Magnifying glass inspected. All components had the same "flow", and/or orifice size (if there were 2 or more like pieces). No burs, trash. Reset, re-seated, re-installed. very clean set of carbs. no gunk,junk,slime, anywhere.

NOTE: Right side exhaust header pipe (sitting on bike) still, is much cooler than the left. I can keep my hand on it (and this was after letting bike run for about an hour with the Sea foam).. A quick touch of the left header is all you needed to know it was skin blistering worthy. (makes me wonder if this was the reason mixture screws were set at 3 on one carb, and 3-1/2 turns out on the other?)

All hoses were cleaned, firmly, and fully installed, and clipped in, as well as a new fuel filter. the entire carb bank, is spotless. ( Choke operation, and idle adjustment screw works MUCH better though.)


(since I don't have the manual yet...)

Main jet (appeared) to be #98. BOTH carb needles had E-clip 3rd slot from top, and TWO washers on top. Is that a stock value? (again, it does have a Yoshi slip on) can anyone confirm or deny this is recommended for slip on and/or stock? AND/OR, I cannot truly confirm when last valve adjustment was done. (supposedly after repair, from an accident) POSSIBLE this related to valves needing adjustment?

[HoneyBadgerRy]

Originally Posted by GAU-8

Did a complete disassemble (again), removed all jets, needles, diaphragms, screws.( anything that could come out, CAME OUT) Let it sit in carb cleaning fluid for an hour, then sprayed all orifices, springs, screws, tubes with a carb cleaner spray. All components had the same "flow", and/or orifice size (if there were 2 or more like pieces). No burs, trash. Reset, re-seated, re-installed. very clean set of carbs. no gunk,junk,slime, anywhere.

NOTE: Right side exhaust header pipe (sitting on bike) is much cooler than the left. I can keep my hand on it (and this was after letting bike run for about an hour with the Sea foam).. A quick touch of the left header is all you needed to know it was skin blistering worthy. (makes me wonder if this was the reason mixture screws were set at 3, and 3-1/2 turns out?)

All hoses were cleaned, firmly, and fully installed, and clipped in, as well as a new fuel filter. the entire carb bank, is spotless. ( Choke operation, and idle adjustment screw works MUCH better though.)


(since I don't have the manual yet...)

Main jet (appeared) to be #98. BOTH carb needles had E-clip 3rd slot from top, and TWO washers on top. Is that a stock value? (again, it does have a Yoshi slip on) can anyone confirm or deny this is recommended for slip on and/or stock?

Stock needles don't have clips.

[genosr1]

did you remove and clean pilot jets, they can be difficult to clean

[HoneyBadgerRy]

Also did you verify all four holes in the pilot circuit flow? To do this you need to spray with the mixture screw slightly unscrewed,, and completely in.

[rojoracing53]

Don't forget to sync the carbs. Maybe a cold header on ideal means something isn't matching between the carbs in the low rpm range. Then when you open it up your only using the main jets and it's all happy.

My understanding was OEM needles don't have a clip that can be adjusted so if yours is adjustable then you have a jet kit installed. There's no need for washer on a proper jet kit.

[jkv45]

Did you bench-sync the carbs while they were off? (rojo beat me by a minute...)

Idle mixture screws have a spring, washer, and o-ring?

[GAU-8]

Originally Posted by HoneyBadgerRy

Stock needles don't have clips.

Thanks for the reminder! I always had a modified bike, completely forgotten that stock has no clips or spacers. Ok so we know the ket kit is after-market.

Originally Posted by genosr1

did you remove and clean pilot jets, they can be difficult to clean

THAT I did do.

Originally Posted by HoneyBadgerRy

Also did you verify all four holes in the pilot circuit flow? To do this you need to spray with the mixture screw slightly unscrewed,, and completely in.

This one, technically no. more info please. anything that had a passage, I cleaned and squirted through. but I did a lot of squirting, and verifying through other orifices in carb body, on exit. THIS could lead somewhere though....

Originally Posted by rojoracing53

Don't forget to sync the carbs. Maybe a cold header on ideal means something isn't matching between the carbs in the low rpm range. Then when you open it up your only using the main jets and it's all happy.

My understanding was OEM needles don't have a clip that can be adjusted so if yours is adjustable then you have a jet kit installed. There's no need for washer on a proper jet kit.

( addressed above, and thank you though for the time)

Originally Posted by jkv45

Did you bench-sync the carbs while they were off? (rojo beat me by a minute...)

Idle mixture screws have a spring, washer, and o-ring?

yes, and yes.

I did synch them today again, though. Idle/low rpm, is on the money (using an electric "synch-mate" or similar sounding name)


surprised by the quick responses, and thanks for your time.

[HoneyBadgerRy]

Originally Posted by GAU-8

Thanks for the reminder! I always had a modified bike, completely forgotten that stock has no clips or spacers. Ok so we know the ket kit is after-market.

THAT I did do.

This one, technically no. more info please. anything that had a passage, I cleaned and squirted through. but I did a lot of squirting, and verifying through other orifices in carb body, on exit. THIS could lead somewhere though....

( addressed above, and thank you though for the time)

yes, and yes.

I did synch them today again, though. Idle/low rpm, is on the money (using an electric "synch-mate" or similar sounding name)


surprised by the quick responses, and thanks for your time.

I will try to explain this as best I can. For starters place the carbs on a work bench with the fuel bowls, floats, and float needles removed (Main jets, jet holder, slide, and needle optional). Now put the mixture screws to 3 turns out and verify that carb cleaner flows through the pilot jet and out of the hole infront of the throttle plate. Screw the mixture screw in and notice how it is now sticking out of the hole carb cleaner just flowed through. Open the throttle plate and you should see some holes just behind where is seats. Spray carb cleaner through the pilot jet and verify that it comes out of those holes.

[GAU-8]

That was the ticket.

I'm guessing spraying down into where the mixture screw was, may have blocked residue, or particulates more. But spraying into those holes, and out, cleared it out. Then doing what you asked, I could verify flow.

Thank you!

Both exhaust headers running same temps, no horrible stumble/ die on low throttle, and RPM stays where its set. And she runs fantastic now.

[pantera]

Originally Posted by GAU-8

That was the ticket.

I'm guessing spraying down into where the mixture screw was, may have blocked residue, or particulates more. But spraying into those holes, and out, cleared it out. Then doing what you asked, I could verify flow.

Thank you!

Both exhaust headers running same temps, no horrible stumble/ die on low throttle, and RPM stays where its set. And she runs fantastic now.

Glad to hear the bike runs well for you now.Ride on...........

[Dsheumaker]

Awesome to see the forum helping someone out that was at a loss. Awesome!

[jkv45]

Glad you figured it out with the help of HoneyBadgerRy.

It sounds like another case of the carb not being absolutely clean before re-assembly. Happens all the time.