06 Ninja - Carb vacuum leak...

[Dramier]

Long story short, my girlfriend bought herself an '06 Ninja 250R. Wasn't running, needed a jump start and a carb cleaning, plus fresh gas and plugs.

Bike jumps up and runs fine, idles fine, revs just fine. The problem is when releasing the throttle, the motor returns to idle very slowly. Skipping through everything I've checked I narrowed it down to a vaccuum leak by spraying carb cleaner until the engine raced.

The problem is the area I'm spraying is on the engine side of the carbs, right where the springs and slides for the choke mechanism are located. It's not the boots, but I can't see anything there that could be leaking and I'm a little stumped.

Basically when I directly spray the choke slide and spring in between the two carbs, the engine RPM rises. I haven't pulled the carbs back out yet because I was honestly hoping to avoid doing that again, but I'm completely stumped. Does anyone have any ideas or has seen this before?

Thanks!

[choneofakind]

There's two little vacuum ports in the middle of the carbs, sure you're not spraying at those when you aim for the choke plungers? Just asking the stupid questions...

[Dramier]

Originally Posted by choneofakind

There's two little vacuum ports in the middle of the carbs, sure you're not spraying at those when you aim for the choke plungers? Just asking the stupid questions...

There's the two on top, one goes to the petcock, the other to the idle coasting.. That's the only two I'm aware of.. In the middle there's the overflow pipe that t's out to the drain line. Are you asking about one of those?

[Ghostt]

If your in need of carburetor services PM @ducatiman for your carburetor services and parts.

https://www.ninjette.org/forums/showthread.php?t=226815

https://www.ninjette.org/forums/show...wpost&t=239678

Here's some pictures that might be helpful.

[choneofakind]

There should be two vacuum lines going to the idle enricher that come from the middle of the carbs and cross over the left carb cap to the enricher.

[Dramier]

Originally Posted by choneofakind

There should be two vacuum lines going to the idle enricher that come from the middle of the carbs and cross over the left carb cap to the enricher.

Got it. We pulled the carbs all the way back out, completely disassembled them and boiled them. Then re-cleaned everything, all passages, double-checked everything and got it all back together.

Still not running quite right, but based on how it's acting I'm fairly confident it needs some mixture adjustments and it will be fine. No more vaccuum leak, and at this point I can tell from the way it occasionally fights itself running that a good mixture adjustment and carb balance will get this Ninja running right. My fingers are soooooo sore. Those carb boots. I could murder somebody over those things.

One other question for you guys.. Stock '06 Ninjas came with single exhaust correct? If so, is it common for people to swap to a dual exhaust by basically adding a second stock muffler? The mufflers on it are Kawasaki stock ones, just one on each side and I thought these bikes came with single exhaust. The carb also had 105 jets in it and I noticed the mixture screw caps had already been removed.

[choneofakind]

No, stock exhaust is a 2-can system.

Stock pilot jets are 38, stock main jets are 105.

[Ghostt]

Don't forget to adjust the valves, odds are they've never been done, If the valves are out of adjustment, it will make tuning/dialing in the bike difficult, if not impossible.


Idle mixture screw tuning:

Your initial setting should be 3 full turns out from the bottom, remember just slightly tighten them, don't go all Conan on them.



Then warm it up, slowly turn 1 side pilot screw in until the rpms drop, then back out till RPM's peak (and no further)* Twist throttle...see how it reacts...tweak to taste.
Repeat on other side... test ride. You're looking for best throttle response and transition from just cracked to 1/4 throttle opening or so.*

Thats a quickie, 10 cent tutorial on setting pilot screws.**

Carburetor synchronization

You can sync with the carbs in hand. Back the idle adjustment off to close that carb then match the second carb to it with the sync screw. You can then turn the idle adjustment up while using a thin feeler gauge (maybe .002") between the throttle plate and the throttle bore, adjust to just fit, and then check the second one and adjust to match. If you have good feel for this it will run fine once installed.

It would do folks well to take a minute to review and understand what a sync tool does, how it works. And take another minute to look at the carb linkage and sync adjustments available to fix irregularities that might occur. It can help take some of the mystery out of this as well as stop unnecessary carb sync screwups.

Meaning, that the carbs were right once, the butterflies were matched and it performed well, but then changed. Undecided And the problem somehow occurred in the butterfly direct shafts, or the sync screw turned or wore that pad that it rests on, or the carburetor pairing/ bridging brackets twisted in relation to each other, and enough so that the butterflies no longer operated in sync, such that performance noticeably suffered. And a fix will be accomplished by changing the butterfly position, the only thing the sync adjustment does. Hmmm. Really? Undecided

Meanwhile, the tool measures vacuum at each individual runner. That's all it does, how it works. And vacuum is effected by a huge list of things, butterfly position being only one of them, and the only one addressed with that tool while turning those sync screws. The rest of that list includes, valve adjustment, jetting, float level, compression differences between cylinders caused by wear as well as factory CC differences in the head, intake runner, as well as flow by port variations, etc. Variations in cams, wear or factory tolerance. Then there's the potential big one, pilot jets and pilot screw mixture settings. All of those effect the vacuum and will be read by the sync tool, accurately identifyng the difference that exists, and with the only adjustment being used to "correct" the problem, move the butterfly relationship, one to the next.

It's that clear understanding that has me of the opinion and long time practice to not touch the sync screws on a set of carbs that were right once and were never dismantled from the rack. And jet cleaning as well as float needle changing doesn't require that they be dismantled. And further, if I DID dismantle a set of carbs, I just matched the butterflies on the bench at assembly, using a feeler gauge, and then never touched them again, never gave them another thought.

That method, properly executed, will have THAT portion of the complete equation, balanced flow to each cylinder in a multi-cylinder/ carb application due to butterfly position, satisfied entirely adequately. And in fact, it has worked for me every time I've done it on every bike (as well as individual runner/ butterfly V-8 intakes, all eight) that I've ever owned or any that I've fixed for others. And the times I fixed for others was usually after an attempt by others to sync the carbs, chasing a problem, or sometimes not even chasing a problem, but one they created wth a sync tool, chasing a problem from that list, that was never a butterfly position change problem. Those linkages are so direct and simple that they don't know how to screw themselves up. Not enough to care about.

I'm sure this will start a lot of controversy so I won't argue it, just offering it for those who understand the whole picture that I outlined and might make good use of it. It is what I've done, on every engine I ever worked on, including blue printed racing engines as well as regular old, high mileage street stuff. I've had at least four, four cylinder bikes with over 100,000 miles that ran quite well, the whole time, and never had a carb sync performed. When they did finally get a total disassembly, this is how I set them up, on the bench. Over the years I've straightened out at least a half dozen messed up ones, probably more, and on the bench, after fixing the original problem which was fouled pilot jets.

I only posted this because it seems like its coming up fairly often, especially with problems from a sync gone bad. One I would suggest was never a sync problem to begin with. A big or sudden change in performance is NEVER a sync problem. NEVER. Remember that. Cool If there is a problem, and you connect the gauges? YES, there will definitely be an imbalance indicated. But because that hole has a problem that is from the rest of the list. A bad plug, a plugged pilot jet, a screwed up float, a bad valve or setting, etc. Every one of them effecting the vacuum in the intake but NOT from a sudden move of a butterfly position, a sync adjustment.

[Dramier]

Rock on, great info and I really appreciate you taking the time to spell it out for me. Will do the idle mixture tweak in the next day or two and see how it goes.

We thought we had the return to idle slowness resolved, but it came back once the bike warmed up. Going to have to recheck for vaccuum leaks and see if we somehow missed something. Will report back on progress and see what you guys think.

I learned to wrench on motorcycles, but I never learned much about carbs as we had a guy in the shop who was a genius with them. By the time I went to college for auto tech it was all fuel injection. I feel like there is something obvious I'm missing simply because I'm not familiar with carbs, but so far it is continuing to elude me. Everything I've searched and read online seems to indicate a slow return to idle is a leak somewhere, but a thorough inspection of every line and all the boots turned up nothing. Everything seems to be seated properly as well. I'm beginning to think I may have to borrow a smoke machine and see what that turns up.

[Ghostt]

Another thing to check is the slides, make sure they are installed properly, and they didn't get pinched when you installed the black covers, make sure they fit into the groove in the body of the carburetor.

Also when you cleaned them, did you remove the idle mixture screws? Did you verify all the fuel circuits were clear with an air compressor? Remove the jets, and holders? Verify that ALL was.clear? Set the float height? Did you replace any parts? Assembled them properly? Check peacock for proper operation? And leaks, both fuel, and vacuum? Did you install a inline fuel filter? Check linkage for proper operation? Cables checked for binding? Cables lubricated?

A lot of people try cleaning the carburetors, with mixed results, the fuel circuits are extremely small, and if gummed up take more than a can of carburetor cleaner. Once again I recommend to PM @ducatiman to have the carburetors refurbished, they will be better than new when he's done, and 1000% right.

[Dramier]

Originally Posted by Ghostt

Another thing to check is the slides, make sure they are installed properly, and they didn't get pinched when you installed the black covers, make sure they fit into the groove in the body of the carburetor.

Also when you cleaned them, did you remove the idle mixture screws? Did you verify all the fuel circuits were clear with an air compressor? Remove the jets, and holders? Verify that ALL was.clear? Set the float height? Did you replace any parts? Assembled them properly? Check peacock for proper operation? And leaks, both fuel, and vacuum? Did you install a inline fuel filter? Check linkage for proper operation? Cables checked for binding? Cables lubricated?

A lot of people try cleaning the carburetors, with mixed results, the fuel circuits are extremely small, and if gummed up take more than a can of carburetor cleaner. Once again I recommend to PM @ducatiman to have the carburetors refurbished, they will be better than new when he's done, and 1000% right.

We disassembled everything in the carbs twice, second time through we boiled them and cleaned. Checked proper assembly twice, verified everything was working multiple times as we assembled them and several times before re-installing in the bike. I feel pretty confident the carbs are clean. I did not check or set the float height, but there is definitely gas reaching the bowls and nothing coming out of the overflow. We removed the petcock from the tank, cleaned it, and verified it works by applying vaccuum to it and watching gas come out on the "on" and "res" positions and nothing coming out on the "off" position.

I checked the cables and inspected them for kinks and binds. Inspected the choke and made sure it's moving and working correctly. I did not install an in-line fuel filter though yet, will definitely be doing that once I get this worked out.

I'm feeling almost 99% certain this is a vaccuum leak at this point based on the engine race when carb cleaner is sprayed in between the carbs. I just can't figure out where the heck it's pulling it in at. Unless it's a tiny pinhole or a crack that I've somehow missed in pulling the hoses off and inspecting them inch by inch. From what I understand, the only thing that will cause a slow return to idle is unmetered air if the cables and mechanical linkages are working correctly.

If the overflow T fitting between the carbs had a crack or hole in it, would it be pulling a vaccuum or otherwise admitting outside carb cleaner spray into the carb? I'm thinking this is a hairline crack somewhere.

[Dramier]

https://www.youtube.com/watch?v=At74...ature=youtu.be

This is way way better than it was yesterday after tweaking the mixture screws gently. This is with no choke, and the engine already warm. To me it still seems way slow on the return to idle, although I will say the engine sounds right but the tach seems slow. My vulcan idles down way faster than this, but I don't know what's 'normal' for a Ninja 250, so I leave it to you guys to take a look and tell me if that's still slow or if that's right.

[Ghostt]

Seems right to me, but the idle seems low? It should be about 1,300-1,500 RPMs, with the engine all warmed up.

[Dramier]

Originally Posted by Ghostt

Seems right to me, but the idle seems low? It should be about 1,300-1,500 RPMs, with the engine all warmed up.

It is too low. I'm used to working with cars and having a low idle all the time. Will have to tweak that back up and re-adjust. Going to remove the chin and take her down the road a bit tomorrow and see how she does under load and through the gears.