Shimmed my 250R, now dies when revved

ender323 · August 6th, 2017, 05:05 PM

Hey all,
I had my 09 250r taken apart for paint, and decided to go ahead and desnorkle and shim the carbs while I had it apart. I added 2 washers to each needle. It previously seemed a bit lean (ran fine once warmed up, but needed a fair amount of choke to get it warm). Now, I started it up, warmed it up (with a bit of choke despite the shims) and when I tried to ride off, it seemed to hit a lean spot around 3-3.5k revs. I can barely get it past it if I modulate the throttle a little, but it generally dies after it hits 3-3.5k. I figured this was it running lean, and decided to put the snorkel back on. This did not seem to affect the issue. I'd rather not open my carbs back up if I don't have to, it was a pain in the ass the first time. Any advice on what could be happening here?

DannoXYZ · August 6th, 2017, 07:11 PM

So the 3-3.5k-rpm behavior is worse now than before?

ender323 · August 6th, 2017, 07:38 PM

Yes, significantly. It used to just need to be warmed up for a couple minutes with choke, and seemed a little lacking in the low end of the rev range but not terrible. Now it revs up to 3-3.5 and then either takes several seconds to get past that or just slowly drops in rpm and stalls out/dies.

DannoXYZ · August 6th, 2017, 08:01 PM

What quantitative data have you collected and analyzed to indicate that you have lean mixture as causing your issues in the 3-3.5k-RPM range?

ender323 · August 6th, 2017, 08:37 PM

Quote:

Originally Posted by JacRyann

What quantitative data have you collected and analyzed to indicate that you have lean mixture as causing your issues in the 3-3.5k-RPM range?

Like I said, it was just a guess. AFAIK, it's either dying because it's rich or lean and I don't smell unburnt fuel. Doesn't seem like I messed up the throttle or choke cable, if there's another reason for it to be dying I'm eager for advice.

KikRox · August 6th, 2017, 09:03 PM

Heh did you make sure your needles are seated properly in the slides and sitting down in the jets? Once i have them lined up i give them a very gentle push with the blunt side of my tweezers. That'd be my first guess... easy mistake to make. or did you cover one of the holes in your slide diaphragm with the foot on one of your springs? (the white part on the end of the spring has feet, down in the hole there is a small hole that lets your slide actuate freely if obstructed it may cause an issue)

ender323 · August 6th, 2017, 09:11 PM

Quote:

Originally Posted by KikRox

Heh did you make sure your needles are seated properly in the slides and sitting down in the jets? That'd be my first guess... easy mistake to make. or did you cover one of the holes in your slide diaphragm with the foot on one of your springs? (the white part on the end of the spring has feet, down in the hole there is a small hole that lets your slide actuate freely if obstructed it may cause an issue)

I think I'm going to pull the carbs completely tomorrow and open them up and take a better look. Thanks for the ideas, I'll be sure to check that. I'm also a little concerned that the washer may be too large. I could only find #6 washers, most people talk about metric sizes but I think that's closer to a #4. I will try to find some #4s tomorrow-should the washer fit completely inside the foot on the spring? Or should they be as large as the foot?

DannoXYZ · August 6th, 2017, 09:14 PM

Quote:

Originally Posted by ender323

Like I said, it was just a guess. AFAIK, it's either dying because it's rich or lean and I don't smell unburnt fuel. Doesn't seem like I messed up the throttle or choke cable, if there's another reason for it to be dying I'm eager for advice.

Well, we have more data to work with now. Seems adding fuel made it worse. So we want to go in the opposite direction and remove fuel in that range, simple enough. I was seeing if you have any datalogging from wideband.

A lot of bikes have a problem with richness in mid-range. Due to helmholz resonance effects, air goes in, is pushed back by pressure-wave, and sucked back in again, leading to three passes through carbs and way too much fuel.

Ghostt · August 6th, 2017, 11:20 PM

Take a good look and make sure the diaphragms are seated properly, and not pinched, damaged, etc....

ducatiman · August 7th, 2017, 05:58 AM

Quote:

Originally Posted by ender323

Yes, significantly. It used to just need to be warmed up for a couple minutes with choke, and seemed a little lacking in the low end of the rev range but not terrible. Now it revs up to 3-3.5 and then either takes several seconds to get past that or just slowly drops in rpm and stalls out/dies.

More is not necessarily better. I think you addressed the wrong circuit...to correct extended warmup, you want to tweak the pilot circuit a bit.

Suggestions....remove the shims...turn each pilot screw out in 1/4 turn increments riding, testing warmup charactaristics with each change. This entails allowing to fully cool between sessions and may require carb removal, drilling and removal of the pilot screw tamper caps (if not already removed). Avoid the temptation to make huge, radical, all at once changes. Patience, testing between changes.

***********************************************************
Coincidentally, I'm currently working on an owners 250 carb set with pilot jets drilled to a MASSIVE oversize. Owner, understandably, reports black, fouled spark plugs, inability to easily start/idle/transition.
Undiagnosed (till now) ...likely the real reason the bike was sold/changed hands.

Though they are marked as stock 38 pilots...stock is .016" these drilled to .036" WOWSERS! Obvious solution? Return to new, stock size 38 pilot jets (which I keep in stock)

A very poor decision to drill pilots to such an extent. Radical jetting changes as this are rarely (if ever) needed. Small, measured, deliberate steps, always testing between...and only for good reason, IMHO.

jkv45 · August 7th, 2017, 06:25 AM

Did you remove the caps on the idle mixture screws while the carbs were off and set them to a base of 2.5 turns out? That usually helps get better running in the idle to 1/8 throttle range.

When working with carb issues, think in terms of throttle position (1/8, 1/4, 1/2, etc) and not RPMs. 2 shims may be too much for you, or something is not assembled correctly in the carbs.

August 6th, 2017, 05:05 PM	#1
ender323 ninjette.org newbie Name: Nicholas Location: Chicago/Boston Join Date: Jul 2017 Motorcycle(s): '09 Ninja 250R Posts: 4	Shimmed my 250R, now dies when revved Hey all, I had my 09 250r taken apart for paint, and decided to go ahead and desnorkle and shim the carbs while I had it apart. I added 2 washers to each needle. It previously seemed a bit lean (ran fine once warmed up, but needed a fair amount of choke to get it warm). Now, I started it up, warmed it up (with a bit of choke despite the shims) and when I tried to ride off, it seemed to hit a lean spot around 3-3.5k revs. I can barely get it past it if I modulate the throttle a little, but it generally dies after it hits 3-3.5k. I figured this was it running lean, and decided to put the snorkel back on. This did not seem to affect the issue. I'd rather not open my carbs back up if I don't have to, it was a pain in the ass the first time. Any advice on what could be happening here?

August 6th, 2017, 11:20 PM	#9
Ghostt in your machine Name: Scott Location: Summer Shade, Ky. Join Date: Oct 2014 Motorcycle(s): 98 Ninja 250/F12 aka ZX-2R "SERENITY", 91 Ninja 500/A5 aka ZX-5R "Phoenix", 84 Honda GL1200A "SIREN" Posts: A lot. Blog Entries: 25 MOTM - Jun '17, May '16, Mar '15	Take a good look and make sure the diaphragms are seated properly, and not pinched, damaged, etc.... __________________________________________________ *violente et ignorantia* ZX-2R BLOG *Twitter and Instagram = Ghostt_Scott* *I'm not here to change your mind, just to inform.*
	1 out of 1 members found this post helpful.

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August 6th, 2017, 07:11 PM	#2
DannoXYZ ninjette.org certified postwhore Name: AKA JacRyann Location: Mesa, AZ Join Date: Dec 2011 Motorcycle(s): CB125T CBR250R-MC19 CBR250RR-MC22 NSR350R-MC21 VF500F CBR600RR SFV650 VFR750F R1M ST1300PA Valkyrie-F6C Posts: A lot. MOTY - 2018, MOTM - Nov '17	So the 3-3.5k-rpm behavior is worse now than before?

August 6th, 2017, 07:38 PM	#3
ender323 ninjette.org newbie Name: Nicholas Location: Chicago/Boston Join Date: Jul 2017 Motorcycle(s): '09 Ninja 250R Posts: 4	Yes, significantly. It used to just need to be warmed up for a couple minutes with choke, and seemed a little lacking in the low end of the rev range but not terrible. Now it revs up to 3-3.5 and then either takes several seconds to get past that or just slowly drops in rpm and stalls out/dies.

August 6th, 2017, 08:01 PM	#4
DannoXYZ ninjette.org certified postwhore Name: AKA JacRyann Location: Mesa, AZ Join Date: Dec 2011 Motorcycle(s): CB125T CBR250R-MC19 CBR250RR-MC22 NSR350R-MC21 VF500F CBR600RR SFV650 VFR750F R1M ST1300PA Valkyrie-F6C Posts: A lot. MOTY - 2018, MOTM - Nov '17	What quantitative data have you collected and analyzed to indicate that you have lean mixture as causing your issues in the 3-3.5k-RPM range?

August 6th, 2017, 09:03 PM	#6
KikRox ninjette.org member Name: Nein Location: Canada Join Date: Jun 2017 Motorcycle(s): 2011 Ninja 250r se Posts: 100	Heh did you make sure your needles are seated properly in the slides and sitting down in the jets? Once i have them lined up i give them a very gentle push with the blunt side of my tweezers. That'd be my first guess... easy mistake to make. or did you cover one of the holes in your slide diaphragm with the foot on one of your springs? (the white part on the end of the spring has feet, down in the hole there is a small hole that lets your slide actuate freely if obstructed it may cause an issue) __________________________________________________ They should give me my own section called kik rox is a silly **** who breaks stuff.

August 7th, 2017, 06:25 AM	#11
jkv45 Rev Limiter Name: Jay Location: WI Join Date: Jul 2013 Motorcycle(s): '06 SV650n, '00 Derbi GPR, '64 CA77 Dream 305, '70 CL450 Scrambler, numerous dirt bikes Posts: A lot. MOTM - Jun '18, Oct '16	Did you remove the caps on the idle mixture screws while the carbs were off and set them to a base of 2.5 turns out? That usually helps get better running in the idle to 1/8 throttle range. When working with carb issues, think in terms of throttle position (1/8, 1/4, 1/2, etc) and not RPMs. 2 shims may be too much for you, or something is not assembled correctly in the carbs.