Rough acceleration

[erbarry88]

Just replaced the engine with what they claim only had 5k miles but had been sitting for about 9 months. First startup was really rough with the old fuel that was in the tank but after draining it and adding new fuel it ran a bit better. I then synced the carbs and it began to idle fine. Giving it throttle inputs seemed to rev up just fine on the stand. I took it out for its first ride and seemed very sluggish and sputtering at low rpms. Once I got past 8k it seemed to smooth out but getting there was a pain. The bike sat in the garage for about 10 months and I didn't do anything to the carbs but sync them when I replaced the engine. The bike ran great with the old engine but when I synced the carbs with the new engine I noticed that the screw went in a lot, it almost compressed the spring completely. I'm thinking I have to pull the carbs out and clean them

[Motofool]

Originally Posted by erbarry88

....... I'm thinking I have to pull the carbs out and clean them

You are thinking correctly.

[Ghostt]

Your carburetors are in need of a deep cleaning, Pm @ducatiman for your carburetors needs and services.

As far as your attempt at synchronization, that was a mistake, and here's why,

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.

[erbarry88]

Originally Posted by Ghostt

Your carburetors are in need of a deep cleaning, Pm @ducatiman for your carburetors needs and services.

As far as your attempt at synchronization, that was a mistake, and here's why,

That's what I figured after my first run and the amount of adjusting I had to do to idle properly. What I don't understand on what you quoted is that it mentions to adjust the second carb to the first one but what am I adjusting? Sync screw, idle adjustment, idle mixture?

[Ghostt]

I'm assuming your referring to this,

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.

I'm referring to the carburetors synchronization screw, your adjusting the butterflies so they are exactly the same. Matching the second one to the first.

[erbarry88]

Originally Posted by Ghostt

I'm assuming your referring to this,



I'm referring to the carburetors synchronization screw, your adjusting the butterflies so they are exactly the same. Matching the second one to the first.

Ok, I'm probably just overthinking it. Once I have the carbs in front of me I should be able to figure it out.

[Ghostt]

Be sure if your gonna clean the carburetors, to remove all the jets, holders, idle mixture screws, etc.... Clean all the fuel circuits, and verify all fuel circuits are clear with an air compressor.

Also check float valves, and float levels.

[Ghostt]

Another options,

https://www.ninjette.org/forums/showthread.php?t=246349

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

[spooph]

why did you replace the engine if it was running great?

[erbarry88]

Originally Posted by spooph

why did you replace the engine if it was running great?

It was running great until I put a hole in it right under the front sprocket.

[spooph]

Originally Posted by erbarry88

It was running great until I put a hole in it right under the front sprocket.

lol, that would do it! I agree with the others. A thorough carb cleaning is in order.

[erbarry88]

So I cleaned the carbs, synced them, adjusted the mix screws 2.5 turns out and added 2 washers to the needles and it ran great. Smooth acceleration all the way up to redline. Thank you all.

[Ghostt]

Did you replace the fuel filter? Did you do the bench synchronization method?

[erbarry88]

Originally Posted by Ghostt

Did you replace the fuel filter? Did you do the bench synchronization method?

I removed that tiny filter and bought a bigger one at autozone and yes I did the bench sync.

[Ghostt]

What did the bench synchronization tell you?

[erbarry88]

Originally Posted by Ghostt

What did the bench synchronization tell you?

That I completely jacked it up when I tried syncing it with the bottle method. Seeing what happens when you move the sync screw you get a clear picture on how it affects the butterflies and how uneven you can make them.

[Ghostt]

Now you understand, very good, glad you got it all sorted out.