Small sputter on light accel?

[Stevo555]

Hoping one of you can interpret the cause of a small, single stutter , on early throttle roll on .
Pulling away from stop, with light acceleration, and I seem have a small bobble , and then off she goes.

Doesnt happen under more aggressive starts .
I just cleaned my pilot jets , and carbs and moved all 4 air screws to 2.25 turns from 2.5 …
After market pipes , not sure if the needles are shimmed, but unlikely.

Seem to recall pops on accel mean one thing and pops on decel are another, but suspect one you have some ideas .

Butt dyno seems to feel some impressive power all the way to 11k revs though outside of the minor low end annoyance.

Thanks if you get a minute …

[gregness]

So... some research showed that a stumble or hesitation on acceleration is often associated with a lean condition. If you have a better-flowing after-,market exhaust I would try shimming the needles. I did mine when I put pipes on back in the day, and the bike ran better after that mod. Also not an expensive thing to try...

[CHARLIE]

I did the shim thing to mine in 03 with stock pipes. Stutter was around 4k rpm. Never looked back. Put some carbon slip-ons on a few years later, ran just as well if not better. Been this way for a long time. Runs like a beast.

[Stevo555]

Thanks guys , I was thinking there was a
method to your madness back in the day .
I think I made enough mistakes pulling the carbs off to clean the jets , that I feel much better that I won’t repeat them again to try the shims. Going into the rubber bellows seemed scary so rolled the dice and seem to have lost!

I will continue with my Fuel Injection envy.
S

[CYACOP]

What was your procedure for syncing the carbs?

[BillDownUnder]

I use one of these.

[M.Rad.]

Could it be dirty pilot jets? Not completely clogged but enough to reduce the amount of fuel before transitioning to the needle jet circuit? Then, once you get past the transition point it works ok...

[Leo]

Did you solve your issue? From experience, when the O-ring around the 'finger' that protrudes into the fuel bowl gets hard, it causes a similar issue. This is not the rubber gasket that seals the fuel bowl itself to the body of the carb. This is an O-ring around the casting that a large brass jet is threaded in to and this O-ring seals into the a machined recess near the very middle of the bowl. This little O-ring gets brittle and cracks or just quits sealing...but it is very important to the light throttle input issues that you have described.

[Stevo555]

Did you solve your issue? From experience, when the O-ring around the 'finger' that protrudes into the fuel bowl gets hard, it causes a similar issue. This is not the rubber gasket that seals the fuel bowl itself to the body of the carb. This is an O-ring around the casting that a large brass jet is threaded in to and this O-ring seals into the a machined recess near the very middle of the bowl. This little O-ring gets brittle and cracks or just quits sealing...but it is very important to the light throttle input issues that you have described.

Hi there,
appreciate the tips. I have not had much time to play , and if I ride it aggressively, I am not getting a major occurrence on the slight pause on light throttle. It is still there .

I confess I just yanked the carbs, cleaned the pilot jets , checked the mains , and needle seats and float needles . No syncing. I did not do a full rebuild . I may need to do a more thorough job later .

[Leo]

I confess I just...

No judging from me. I was in my carbs a few times before I realized these O rings even existed. The first time I poked at one it crumbled like the ash of a cigarette held by a passed out drunk.

Your symptoms have all of the symptoms of hard or cracked O-rings. Pull the carbs and replace only these O-rings and reinstall. I will buy you a drink of your choice if I am wrong...hell, I'll even send you 4 of the O-rings if I can find them in my spare parts pile.

[M.Rad.]

That O-ring is the reason I use ZX11 carbs on my ZZR1200 engine in my ZX11/12. I read somewhere that they are difficult to find, although how hard can it be to find an O-ring?
I just didn't want to have ONE MORE THING to worry about. The carbs actually have the same designation, and no one has been able to tell me what the differences are except for that O-ring thing. Oh, and it works flawlessly throughout the rev range, as far as I can tell.

[Stevo555]

Did you solve your issue? From experience, when the O-ring around the 'finger' that protrudes into the fuel bowl gets hard, it causes a similar issue. This is not the rubber gasket that seals the fuel bowl itself to the body of the carb. This is an O-ring around the casting that a large brass jet is threaded in to and this O-ring seals into the a machined recess near the very middle of the bowl. This little O-ring gets brittle and cracks or just quits sealing...but it is very important to the light throttle input issues that you have described.

My infrequent cough, is becoming more common, and a nuisance . So time to replace all the O-rings. Leo, I am intrigued as to which O-ring, and "finger" you are referring to .

1) Is it the Float Pin and Float Pin Seat O- Ring I should focus on ?

Float Valve Assembly .jpg

OR
2) Is it the Pilot Screw O-Ring thats the culprit.... or less likely, but possibly the Main Jet O-ring? ( my issue is at low throttle, Pilot range)
Pilot Screw or Main Jet O-rings.jpg

I will be replacing all of them, but I am curious as to which one I should be concentrating on .....

Appreciate the feedback so far .....

Steve

[Moise]

It's the main jet o-ring. I don't really understand why, but mine started to crack when the bike was about 8 uears old. A new set and the bike ran fine again.

Sent from my SM-G980F using Tapatalk

[Stevo555]

Thanks Moise ! , and all… Kit on order .

[Stevo555]

Update.... installed an AllBalls kit with all fresh rubber , main Jet ( 150) , pilot jet (40), new needles, and Air Screws/ Pilot screws, and o rings.....
Same cough sputter ..... also confirmed my needles had been shimmed already ... so that was not a factor..... It is a rocket ship under heavy throttle. Never noticed the wheel coming off the ground before. But kind of irritating under more mundane acceleration....

When I first put on my new Delkevic Shorty's I did go into my carbs and set the Pilot Air Screw out 2.5 turns ...... the coughing began this spring when I took my carbs off to clean my existing
jets, etc .... and I set the Pilot Screw to 2.25 turns to try to reduce the fuel smell at idle..... Is it that it?? I was thinking that only impacts idling?

Would this minor adjustment create the cough on throttle levels up to 1/4 ? It coughs under low rev, with some load .... up an incline at 2000-3000 rpm ... and sputtery at low throttle without load ..

I hate to have to take all that plastic off again ... and tank .... Grrrrr