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Old October 9th, 2019, 03:36 PM   #1
vtrider
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Misfiring, bogging at specific RPM (7.5K-8.5K) !

Hello,

I have a 2009 ninja I just got that runs well *except* for between 7.5K and 8.5K rpm, in all gears except for 1st, going on flat, up or downhill. If I keep it at wide open throttle, it can eventually just barely make it through the dead zone and runs great at 9K and above...

It *sounds* to me like it's getting too much fuel in this rpm range, or the spark is missing, because it sounds gurgly, sputtery, loses power, and if I blip the throttle or let go it backfires in the exhaust. It runs really poorly in this range, almost total loss of acceleration.

I'm a little mystified because like I said the problem is just in this specific rpm range, and happens while going down and up hill at the same rpm consistently, so it's not very closely connected with engine load, apparently.

I've done a bit of homework on this, have read these threads, as well as one about a Gummy Bear (?) stuck in the snorkel:

https://www.ninjette.org/forums/showthread.php?t=10208
https://www.ninjette.org/forums/showthread.php?t=186165
https://www.ninjette.org/forums/showthread.php?t=335914

I just bought it. 2009 250r with 11,000 miles that had been sitting for 4 years with gas in the carbs. Wasn't running when I bought it, so I took apart the carb and there was ethanol residue buildup. Thoroughly cleaned the carbs, jets were clogged. New fuel and oil+filter.

I think everything is stock except for Yoshimura exhaust and carb setup:

Clip-type main jet needle, 3 spots down
Idle screws 2 1/4 turns out

I'm going to change the plugs, inspect the snorkel, double-check the vacuum lines on the carb, spray carb cleaner at vaccuum and intake manifolds to check for air leaks, maybe try removing filter and snorkel, check the fuel filters, check the coil lines. If the bike was mechanially advanced, the points would be the first thing I'd be checking -- but has anyone ever heard of the ECM doing something like this?

One note that might help is that I'm starting it without the choke -- it basically dies if I put the choke on when it's idling.

I'll see if I can strap a camera to myself to get some video/audio on the condition.

Anyway, thanks for reading this, would be very grateful for any thoughts or additional things to check, thanks.


Ethan
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Old October 9th, 2019, 07:43 PM   #2
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Hi and welcome to Ninjette!

Please outline in detail procedure used to clean carbs. For bike that sat for that long, more than “carb cleaning” is necessary. More like complete disassembly down to every single nut & bolt and individual component is necessary. Replace all O-rings and seals. Every internal passage thoroughly scrubbed and flossed. New jets. Ultrasonic soaking for weeks on end in radioactive caustic solvents. Micro soda blasting @ 100000psi. Do search for “clean carbs ducatiman” for threads with photos and type of cleaning needed.

You can also troubleshoot by collecting more data. Set needle clip in top #1 position for least amount of fuel. Then try #5 position for most fuel. Which position improves running best?

Also post photo of your needles. There's been cases of incorrect needle tapers causing this issue.

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Old October 10th, 2019, 07:19 AM   #3
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Something inside the carbs is not right.

Are the Needle Jets ("collars") in place? They stick up from the bottom of the venturi and the Jet Needle drops into them.

https://faq.ninja250.org/images/e/eb/Jim_carb_2.jpg
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Old October 10th, 2019, 07:55 AM   #4
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Hello,

Thanks for your replies! Sounds like taking the carbs apart and verifying everything is the first order of business.

Iíll do that and report back.

Best wishes
Ethan
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Old October 10th, 2019, 08:32 AM   #5
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Here's picture of some needles. Which one does yours most look like?

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Old October 10th, 2019, 08:48 AM   #6
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Originally Posted by vtrider View Post
Hello,

Thanks for your replies! Sounds like taking the carbs apart and verifying everything is the first order of business.

Iíll do that and report back.

Best wishes
Ethan
Also closely inspect the rubber diaphragms for tears when you have the carbs off and make sure all passages are clear. Be sure to remove the idle mixture screws, clean the passages, check the o-rings, and set them to 2.5 turns out for starters.
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Old October 10th, 2019, 09:04 AM   #7
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Really sounds like the needle and mainjet not in harmony. If you know the type of jet kit which was used, the jetting database would be of help to get you in the ballpark. Dynajet jets numbers do not match keihin jets.

Ninjettes naturally have a flat spot in that rpm range.

You can experiment with using the choke in that rpm range. If choke helps, the mixture is lean in that rpm range.
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Old October 10th, 2019, 09:55 AM   #8
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Well went to take the carbs off and found that the petcock has become faulty since I put the bike back together -- after removing the vacuum line and the fuel line from the petcock, fuel would continuously drain out, no matter the position of the valve.

I've got a rebuilt kit in the mail, thinking at the very least this won't be helping things, but I wonder if this could explain the problem by itself?

I'll get the carbs apart again and document things to get your take on the PO's setup / condition.

Thanks!
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Old October 10th, 2019, 10:29 AM   #9
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Originally Posted by Dave Wolfe View Post
Really sounds like the needle and mainjet not in harmony. If you know the type of jet kit which was used, the jetting database would be of help to get you in the ballpark. Dynajet jets numbers do not match keihin jets.

Ninjettes naturally have a flat spot in that rpm range.

You can experiment with using the choke in that rpm range. If choke helps, the mixture is lean in that rpm range.
Note that NONE of the numbers in jetting-DB is for newgen (08-12) bikes. And they don't have any before AFR readings from wideband-O2 or dyno, so results are questionable.

What happens most times is carbs get clogged over time. Rather than disassembling and doing proper cleaning, people just install larger and larger gets over time to make up for clogged carbs. But hey, it works better after installing larger jets, so obviously factory ones were too small right? Except you keep on having to upsize jets over and over again as carbs gets more clogged.
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Old October 10th, 2019, 12:23 PM   #10
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Note that NONE of the numbers in jetting-DB is for newgen (08-12) bikes. And they don't have any before AFR readings from wideband-O2 or dyno, so results are questionable.

What happens most times is carbs get clogged over time. Rather than disassembling and doing proper cleaning, people just install larger and larger gets over time to make up for clogged carbs. But hey, it works better after installing larger jets, so obviously factory ones were too small right? Except you keep on having to upsize jets over and over again as carbs gets more clogged.
Are you referring to the jetting database thread in these forums? They're mostly 08-12 bikes.
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Old October 10th, 2019, 01:11 PM   #11
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Ah, so they are, sorry. I was mostly perusing jetting sizes and saw lots of 110+ mains, which is what you'd use on pre-gens. New-gens work best by downsizing mains to 96. Jetting DB on FactoryPro website shows most people using 90-94 mains on Stg2 kit.

Maverick9611 has similar mid-range stumbles and tried all sorts of main-jet adjustments to no avail. Turned out he had aftermarket FP pre-gen needles in his new-gen,. Going back to all-stock conguration fixed his mid-range stumble completely.

https://www.ninjette.org/forums/show...17#post1219417
https://www.ninjette.org/forums/showthread.php?t=324987
https://www.ninjette.org/forums/show...61#post1232661

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Old October 10th, 2019, 02:24 PM   #12
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Originally Posted by vtrider View Post
Well went to take the carbs off and found that the petcock has become faulty since I put the bike back together -- after removing the vacuum line and the fuel line from the petcock, fuel would continuously drain out, no matter the position of the valve.

I've got a rebuilt kit in the mail, thinking at the very least this won't be helping things, but I wonder if this could explain the problem by itself?

I'll get the carbs apart again and document things to get your take on the PO's setup / condition.

Thanks!
Leaking petcock won't cause any running issues if you get full-flow when vacuum is applied. In reverse, if petcock doesn't supply enough fuel, then you'd get stumbling from certain RPM onwards. Bike won't rev past 8000rpms, for example. But it won't have momentary stumble in mid-range then pick up back to normal in high-end. This sounds like incorrect fuel settings with jets & needles.

Most common best-running config is downsize mains to 95-96 and shim needle with 2-washers.
http://web.archive.org/web/201703210...k-racing-cheap - scroll down to "The Nuts and Bolts" section, note: "close to perfect" is with full AreaP exhaust and factory jetting.
https://www.ninjette.org/forums/show...00#post1238900
https://www.ninjette.org/forums/show...84#post1250984
Racing Order - Dyno testing
https://www.ninjette.org/forums/showthread.php?t=55927 - Dyno Test %20 more flow and power with stock jetting

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Old October 10th, 2019, 05:31 PM   #13
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Most, or all, of the bikes in that thread with the giant jets have pod filters, don't know if that's an appropriate size still though. I have a full Area P exhaust on mine and a 95 main jet, it's just about perfect AFR.
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Old October 10th, 2019, 07:17 PM   #14
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Yeah, I think those giant jets are to make up for mid-range stumbles and cross-wind issues with pod-filters. But you end up leaving A LOT of high-end power on table due to excessive richness.

My sponsor Spears dyno-tuned my bike at beginning of 2017 season. We tried factory air-box with K&N filter and then pod-filters. Not single bit of difference! While airbox and filter may be restrictive on bigger bikes, for 248cc, they're simply HUGE! About same size as airbox & filter on my CBR600RR with 4x air-flow and 4x power! So freeing up airbox & filter doesn't do anything because the're not restricting anything. Most of restriction on intake-side is in head port-shape and cam-specs.

Exhaust on other hand, can really be improved. Using full exhaust with larger diameter tubing and free-flow straight-through muffler, we got 22% more air-flow and 22% more power. With stock jetting, it was still too rich. Downsizing to 96 Keihin mains brought AFR into more powerful ~12.0 range and gained another 0.5hp or so. Could've gone leaner to 94-95 mains but we didn't want to risk detonation on 110F+ days or getting bad batch of gas.

On street bike that would've been OK, but on race bikes, we want slightly larger safety-margin as it's WOT for 20-minutes at time in much more demanding conditions.
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Old October 10th, 2019, 07:52 PM   #15
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Hello,

Looks like I've got Dynojet type needles

Not sure what size mains jets I have running but just to rule it out I'll go ahead and get some 96 dynojet equivalents (Keihin seem easier to find individual main jets)

Thanks for your thoughts about the petcock issue.

The Yoshimura is just a slip on -- not full.

I pulled the plugs and looks like one cylinder is running leaner, but I don't know how old they are and have new ones on the way.

They were slightly shy of 0.030" so when I get the new ones I might try running them closer to 0.040".

I moved the clips to the second position.

Idle screws have metal and rubber washers; needle jets are both there, diaphragms are healthy.

Also I took a photo for a vacuum line routing sanity check
Attached Images
File Type: jpg IMG_4336.jpg (187.1 KB, 7 views)
File Type: jpg IMG_4367.jpg (124.0 KB, 4 views)
File Type: jpg IMG_4326.jpg (90.7 KB, 3 views)
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Old October 11th, 2019, 12:47 AM   #16
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Coming along with troubleshooting, good job!

I would save some time and test extreme ends, #1 and #5 clip positions and see which one runs better. Also make sure your needle jet is clear of varnish and not installed backwards. Larger opening should face up towards needle.

One way to pre-sync carbs is to measure gap between throttle butterfly and venturi tube with feeler gauge and set both to be same.

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Old October 11th, 2019, 06:22 AM   #17
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Originally Posted by DannoXYZ View Post
Yeah, I think those giant jets are to make up for mid-range stumbles and cross-wind issues with pod-filters. But you end up leaving A LOT of high-end power on table due to excessive richness.

My sponsor Spears dyno-tuned my bike at beginning of 2017 season. We tried factory air-box with K&N filter and then pod-filters. Not single bit of difference! While airbox and filter may be restrictive on bigger bikes, for 248cc, they're simply HUGE! About same size as airbox & filter on my CBR600RR with 4x air-flow and 4x power! So freeing up airbox & filter doesn't do anything because the're not restricting anything. Most of restriction on intake-side is in head port-shape and cam-specs.

Exhaust on other hand, can really be improved. Using full exhaust with larger diameter tubing and free-flow straight-through muffler, we got 22% more air-flow and 22% more power. With stock jetting, it was still too rich. Downsizing to 96 Keihin mains brought AFR into more powerful ~12.0 range and gained another 0.5hp or so. Could've gone leaner to 94-95 mains but we didn't want to risk detonation on 110F+ days or getting bad batch of gas.

On street bike that would've been OK, but on race bikes, we want slightly larger safety-margin as it's WOT for 20-minutes at time in much more demanding conditions.
Ha - people just can't believe that either could be possible!

You mean a K&N filter, pods filters, or richer Main Jets don't give me 10 more HP?

What???
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Old October 11th, 2019, 07:58 AM   #18
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Old October 11th, 2019, 08:45 AM   #19
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Originally Posted by DannoXYZ View Post
Coming with troubleshooting, good job!

I would save some time and test extreme ends, #1 and #5 clip positions and see which one runs better. Also make sure your needle jet is clear of varnish and not installed backwards. Larger opening should face up towards needle.

One way to pre-sync carbs is to measure gap between throttle butterfly and venturi tube with feeler gauge and set both to be same.

OK good idea -- thanks! I'm waiting for plugs, petcock kit and main jets to come in the mail and then will see where she's at.
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Old October 11th, 2019, 10:40 AM   #20
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After some measuring and looking at the very helpful JetsRUs "Identify That Jet" page , it looks like I have a Dynojet DJ type jet.

In order to measure the jet bore diameter, I inserted a tapered needle covered with Prussian Black (sharpie) into the jet and measured the impression it left with the micrometer. Got around 1.09mm / 0.0429 in, which according to this page makes this a Keihin 112 or Dynojet 108, which is somewhat pleasing to me because it aligns with the hypothesis that the bike is running too rich at WOT, and stumbles when it hits the flat spot around 8000rpm, and what you guys have been saying about mistaken rejetting attempts by the PO. In this case especially suspect because they just had a slip-on exhaust. I still need to see whether the snorkel is there but airbox seems stock aside from that.

The stage 2 kit from Dynojet comes with a max jet size of 100.

The stage 3 kit comes with a 110, so it's conceivable my measurement was on the narrow end, and this is what the PO got. Dynojet says this is for "mildly tuned machines using individual filters or velocity stacks".

Anyhow I'll go ahead and get a 96 and 98 (keihin 100 i.e. stock) to try out. Figuring I should stick with Dynojet if I'm not going to change the needle, but who knows if that matters.

Also verified the chokes are in good order (not much to go wrong there) and the needle jets are varnish free and correctly oriented.
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Old October 11th, 2019, 02:48 PM   #21
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OK good idea -- thanks! I'm waiting for plugs, petcock kit and main jets to come in the mail and then will see where she's at.
Which one of needle pictures above match yours best?
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Old October 11th, 2019, 04:03 PM   #22
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Which one of needle pictures above match yours best?
#4 which I think is a Dynojet needle

I posted another reply on this thread but I think it's getting reviewed because there are links in it.
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Old October 11th, 2019, 05:06 PM   #23
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#4 which I think is a Dynojet needle

I posted another reply on this thread but I think it's getting reviewed because there are links in it.
Interesting... those came on Stg2 kit and were designed to add some fuel in mid-range and remove in high-end when doing K&N and full-exhaust. Maybe without all those mods, you're getting too much fuel in mid-range.

Plugs look OK, very rich, certainly not horrible. Stick with factory specs of 0.030-0.032" for gap. Maybe 0.035". Not sure how much more factory coils can deliver. Here's plugs from my '09 street-bike and '08 race-bike after back-to-back 20-minute sessions @ Thunderhill. Factory-jetting completely coated plugs with carbon with +9.0:1 richness (beyond rich-end measureable by wideband). Race-bike with snorkel-delete, K&N, Tyga full-exhaust and DynoJet Stg2 kit with 96 mains.

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Old October 11th, 2019, 05:52 PM   #24
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Hm, my earlier post is still not up, so I'll paraphrase it here:

Took some measurements of the main jets and they appear to be Dynojet DJ type jets, inner bore was roughly 1.09mm so Keihin 112 / Dynojet 108. Looking at dynojet stage kits, my best guess is the PO bought a stage 3 kit which comes with a Dynojet 110 main. Stage 3 is intended for bikes with pod filters. This would help explain the rich bogging at WOT because the bike has a stock airbox (with snorkel removed).

Still not sure I quite understand the mechanics of the "flat spot" being so closely linked to RPM, uphill and downhill (which I imagine would make a big difference on vacuum pressure) but getting this sorted out and seeing where it leaves the bike seems like a good way to go.

I've got some Dynojet 96s and 98s in the mail as well as stock keihin pilot jets, and we'll see how that does.

Do you think the Dynojet needle will work well with the Dynojet 98 main?

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Old October 11th, 2019, 09:39 PM   #25
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Ok so been reading more about CV carbs and I guess I can see how cv slide/needle height can be a function of engine RPM without needing to consider load. More cycles per second, a certain volume of air per second exhausted from the cylinders, greater vacuum..

I’d like to see a graph of engine load, throttle position, vacuum pressure and rpm. Think that would be mighty helpful in understanding this better. See if can track something like that down from google.

Ok well Wikipedia says “The mass flow through the engine is the product of the rotation rate of the engine, the displacement of the engine, and the density of the intake stream in the intake manifold” so almost totally linear to rpm excluding blips relative to fuel mixture.

And from mechanics stack exchange the definition of calculated engine load is:

Quote:
LOAD_PCT = [current airflow] / [(peak airflow at WOT@STP as a function of rpm) *
(BARO/29.92) * SQRT(298/(AAT+273))]
Where:

- STP = Standard Temperature and Pressure = 25 įC, 29.92 in Hg BARO,
- SQRT = square root
- WOT = wide open throttle
- AAT = Ambient Air Temperature (in įC)

Characteristics of LOAD_PCT are:

- Reaches 1.0 at WOT at any altitude, temperature or rpm for both naturally
aspirated and boosted engines.
- Indicates percent of peak available torque.
- Linearly correlated with engine vacuum.
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Old October 11th, 2019, 10:32 PM   #26
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Do you think the Dynojet needle will work well with the Dynojet 98 main?
Yes, that should be in ballpark more than where you are now.

Quote:
Originally Posted by vtrider View Post
Ok so been reading more about CV carbs and I guess I can see how cv slide/needle height can be a function of engine RPM without needing to consider load. More cycles per second, a certain volume of air per second exhausted from the cylinders, greater vacuum..

I’d like to see a graph of engine load, throttle position, vacuum pressure and rpm. Think that would be mighty helpful in understanding this better. See if can track something like that down from google.

Ok well Wikipedia says “The mass flow through the engine is the product of the rotation rate of the engine, the displacement of the engine, and the density of the intake stream in the intake manifold” so almost totally linear to rpm excluding blips relative to fuel mixture.

And from mechanics stack exchange the definition of calculated engine load is:
Yup, you got it. But Wikipedia/StackExchange is simplistic at best and not very accurate in this matter (don't get me started on mechanic's old-wives tales). Look up "Helmholtz resonance" which deals with pulses going back & forth through engine due to valves opening & closing. There's two chains of pulses, one on intake and one in exhaust. At certain RPMs, they work together to use exhaust flow to pull in intake charge and give you strong vacuum. At other RPMs, exhaust actually backs up out into carbs and fights incoming air. This lowers vacuum and messes with your carb's fuel-metering.

There's also slight time-delay in how slides responds to changes in vacuum. So amount of fuel being sent into engine may not match precisely amount of air going in at that time. There's actually variable-range where stumble occurs as function of load X RPM.

Here's 3D map for you of fuel-injected volumes above/below VE=1 (what Wikipedia assumes and StackExchange’s formulae) to achieve 14.7:1 stoich mixtures. Table is LOAD X RPMs, which is proxy for air-mass and is far from linear. And... all these different maps are for exact same engine!. Well, different ones of exact same model with different rates of wear and states of upgrades & tune.



Maps were created on eddy-current load-dyno which holds engine at exact 10% throttle X 500rpm increments for 1-second while AFR is sampled. Then load & RPM incremented to next data-point and AFR sampled and so on.

Idle is lowest corner nearest you, RPMs increase to right and airflow (load) increases to left. You see where VE is highest in mid-RPMs (torque peak), extra fuel added is highest. Then as RPMs increase past torque-peak, VE decreases, torque decreases and additional fuel added is reduced. If an engine had VE=1 all across board as Wikipedia assumes, these maps would be perfectly flat.

For better understanding of how engines work beyond 5% intro Wikipedia gave, you'll want to read these:

Engineering Fundamentals of Internal Combustion Engine - Pulkrabek 2003 Prentice Hall
Flow and Combustion in Reciprocating Engines - Springer, Arcoumanis, Kaminoto 2009 Verlag Berlin Heideberg
Performance Tuning Theory & Practice - Four Strokes - Bell 1981 Haynes
Tune & Modify Automotive Engine Management Systems - Hartman 2004 MBI Publishing


I'm also not certain that issue isn't related to carb-cleaning and how thoroughly you cleaned carbs. Were O-rings and seals replaced? Hidden secret fuel-passages in carb-body scrubbed and flossed? Micro soda-blasting is really needed due to scrubbing shoving fragments of dried petrol deeper into carb-body.

Last futzed with by DannoXYZ; October 12th, 2019 at 05:58 PM.
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Old October 12th, 2019, 09:05 AM   #27
vtrider
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Woah awesome!! Lots to look into here. Many thanks!!

I did a pretty thorough cleaning on the carbs but didn't replace any o-rings because the float bowl ring seemed fine to me (pliable, proud of the surface), as well as the idle mixture screw ring.

Since the carbs are apart waiting for the new jets I'll double check everything and see if I can't get them spotless, and make sure I've hit every internal passage.

Meanwhile I'm working on a total rebuild of a '74 CB350f which had seized up and been seriously neglected.

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Old October 12th, 2019, 06:01 PM   #28
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OOooh... very nice! Did you find what caused seizure?
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Old October 13th, 2019, 07:53 PM   #29
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Hard to say, one of the pistons took some serious elbow grease to break free, due to rust. Could just have been parked and seized that way. The pistons are so small they freeze pretty easy on these bikes I guess.

But there does remain an unsolved mystery of two springs and a metal piece I found in the oil pan.

Poured over parts diagrams and rebuild videos but havenít yet identified them. Seems like the perfect question for sohc4.net but their registration seems to be broken.

Still prepping the cases but will have to figure out where they came from sooner or later!

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Old October 13th, 2019, 07:57 PM   #30
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I actually bought both bikes on the same day! (From two different states)

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Old October 13th, 2019, 08:03 PM   #31
vtrider
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And the ninja once I got her running

Didnít come with any plastics but I sort of like it for now. Certainly makes frequent carb adjustments as Iíve been doing easy.

Stoked for getting her to pull well all the way through the revs.

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Old October 13th, 2019, 09:22 PM   #32
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Wow, what a deal!

I suspect those springs may be part of cam-chain tensioner? I seem to recall them having dual-springs in that era.
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Old October 14th, 2019, 10:56 AM   #33
vtrider
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Ok looks like they're the centrifugal pins from the starter clutch. Since they're not chewed up it's doubtful they're the reason the engine seized. So my guess is they just fell out sometime and they resorted to kickstarting the bike.

Parts 12,13


Edit:

Not really sure how these could have fallen out during normal use. Perhaps someone changed the starter motor at some point? I can imagine that they fell out when I was taking the motor apart but I took the oil pan off before I removed the starter.

Anyhow! This is all a sort of filler because the main attraction here is the Ninja! Patiently awaiting the new parts to arrive.

Last futzed with by vtrider; October 14th, 2019 at 02:31 PM.
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Old October 16th, 2019, 05:25 AM   #34
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Have you taken an actual look at the starter clutch? Any holes or protrusions on the starter clutch OD?

I too think think those parts are from that assembly. In my experience ( with GZ 250s for MSF course) the outer wall, is thin, and those springs and pin, force thier way out often. ( or they are starting to protrude from the outer diameter of the wheel.I do about 3 or 4 starter clutch repairs a year. ( out of 8 or 9 GZ 250's)

After years of service, I could see the same scenario happening though.

OR, the prior mechanic, didn't hear, or feel them fall out, during the last few moments of assembly. Could possibly explain no damage to those parts, getting bounced into the pan.. (?) It's a long shot, but I have seen crazy stuff happen.

Last futzed with by GAU-8; October 16th, 2019 at 08:27 AM.
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