Carb sync problem

[Cra1g]

Alright, so I made the two-bottle contraption using info from the wiki, went out on a ride to warm the bike up, came back, swapped out the vacuum hoses for the bottle hoses, and started up the engine.

Instantly, all of the water from one bottle went into the other bottle and just started bubbling like crazy. I made some adjustments to the screw to see if I could equal it out but neither direction worked.

I'm probably doing something wrong here, so if anyone has any insight on what might I've done wrong, let me know!

[Triple Jim]

It sounds like one side is getting full vacuum and the other side is not. Check to see if you're connected to the carbs correctly.

[Cra1g]

Originally Posted by Triple Jim

It sounds like one side is getting full vacuum and the other side is not. Check to see if you're connected to the carbs correctly.

I'm connecting one of the hoses to where the petcock vacuum hose connects to on the carb, and then I'm connecting the second hose to the same position but on the other carb, which the original hose connects to the coasting enricher I think.

[Ghostt]

Okay my 2¢

You can get a reasonable 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.

[Cra1g]

Originally Posted by Ghostt

Okay my 2¢

Thanks for the input! A lot of useful information. However, I just want to know what I'm doing wrong, if anything. Like Triple Jim said, I'm probably getting full vacuum from one side but not the other, pointing to a problem with the hose setup, but I'm pretty sure I have the hoses connected to the right places and they're snug, but maybe not?

[Ghostt]

Originally Posted by Cra1g

Thanks for the input! A lot of useful information. However, I just want to know what I'm doing wrong, if anything. Like Triple Jim said, I'm probably getting full vacuum from one side but not the other, pointing to a problem with the hose setup, but I'm pretty sure I have the hoses connected to the right places and they're snug, but maybe not?

You might want to switch the water out with ATF fluid, this takes some of the over sensitivity out of using water.

[RacinNinja]

Originally Posted by Ghostt

You might want to switch the water out with ATF fluid, this takes some of the over sensitivity out of using water.

Plus if it gets sucked into the motor it will actually burn. If all that water were to get sucked in while the engine is running, there is a high risk of hydrolock and a bent rod or broken crankshaft.

A little water will just burn as steam and clean your piston crowns all purty like. It takes a fair bit to hydro lock a motor, more than people think but it's still possible.

[Cra1g]

Originally Posted by Ghostt

You might want to switch the water out with ATF fluid, this takes some of the over sensitivity out of using water.

Would just regular oil work? Don't have ATF lying around..

[Triple Jim]

Watch out, if you're really going to suck a bunch of liquid into the engine, oil will hydrolock it just as quickly as water will. Us 2-stroke guys with injection systems have to watch out for leaking check valves if the bikes are parked a long time. Oil puddles in the crankcase chambers, and on the next startup... Bang!

Any oil will work fine, I suspect Ghostt suggested ATF because it's red and easy to see.

[Cra1g]

Originally Posted by Triple Jim

Any oil will work fine, I suspect Ghostt suggested ATF because it's red and easy to see.

Cool, thanks! Also, which direction do I turn the screw to equal out the carbs? I have the right bottle tube connected to the right carb, and the left bottle tube connected to the left carb. Since all the water is being sucked into the right bottle and the left one is empty, which way do I need to turn the screw?

[SLOWn60]

I understand you wish to press on with pressure testing the carb sync but if I can pass on my experience it may cause you to reconsider.

First; some background: carb sync's used to be mercury filled. A very heavy liquid therefore a lot of inertia resisting movement. It also resists foaming & bubbling so it was the perfect liquid for gauges. Oil & water both have much lower inertial resistance and therefore much more of a challenge to get a steady reading!

It was my experience in hindsight that rigging up a tube & oil sync tester was a realative waste of time and I never found the smooth balance point I was seeking due to the over sensitivity of the liquid.

In future; I will not waste my time & money jury rigging a tester but will go straight to the time & tested bench method of measuring butterfly clearances and be done with it in a few minutes rather than the hour or two it took!

[Cra1g]

Originally Posted by SLOWn60

In future; I will not waste my time & money jury rigging a tester but will go straight to the time & tested bench method of measuring butterfly clearances and be done with it in a few minutes rather than the hour or two it took!

What's the bench method consist of? If it's supposedly easier, I'm all for that!

[RacinNinja]

Originally Posted by Cra1g

What's the bench method consist of? If it's supposedly easier, I'm all for that!

Easier is a relative term. You have to remove the carbs vs hooking up a couple hoses and adjusting a screw.

I'd suggest getting a couple of good vacuum gauges rather than using a couple of bottles. Bench sync is good and if you know what you're doing, just as good.

I've used these before. Provided you use the limiting valves to keep the needle from bouncing around, they work just fine. I have a fancier set but it's a 4 pot for my 4 cylinder bikes. You only need two.

https://www.amazon.com/Vacuum-Carbur...rb+sync+gauges

[Ghostt]

Originally Posted by Cra1g

What's the bench method consist of? If it's supposedly easier, I'm all for that!

Read my #4 post in this thread https://www.ninjette.org/forums/show...00&postcount=4

As stated above you need to remove the carburetors, but if you read my post, carburetor synchronization is almost never the issue, there are other more likely issues that causes problems as I posted above.

[Cra1g]

Originally Posted by RacinNinja

I've used these before. Provided you use the limiting valves to keep the needle from bouncing around, they work just fine. I have a fancier set but it's a 4 pot for my 4 cylinder bikes. You only need two.

https://www.amazon.com/Vacuum-Carbur...rb+sync+gauges

Thanks! Also, what are limiting valves?

[SLOWn60]

Originally Posted by Cra1g

Thanks! Also, what are limiting valves?

They are like a water tap and are on the gauges. So you can limit the rate of sensitivity

[Motofool]

Originally Posted by Cra1g

........I just want to know what I'm doing wrong, if anything..........I'm pretty sure I have the hoses connected to the right places and they're snug, but maybe not?

The circles in the picture indicate the points of connection.

If your hoses have been connected to those points, then there is a leak in the hoses, connections or bottle's caps.

Before trying again, you need to make sure that the whole contraption is leak free.
For that, you can pressurize the thing and submerge it in water.

[Cra1g]

So after the first time I tried to sync my carbs failed, I decided to wait and get proper vacuum gauges. Finally got those and then went to go for a ride to warm the bike up.

The bike was being a bit finicky when I first warmed it up. RPMs would be all over the place and I had to do a bit of work to dial in the choke. Went to take off and giving it gas would just make the bike die. Didn't experience anything like this before I messed with the carbs the first time.

I would eventually have to fully turn the choke on, and the bike would sometimes start up and rev up like crazy, so I would turn the choke down just a tad and the bike would die.

I have a feeling I ****ed something up, probably when I adjusted the carb sync screw, but I certainly didn't turn it more than a half-turn either direction. I also ended up getting just a little bit of water in the carbs using the bottle method. Do you think either of these things played a role?

[Ghostt]

A half turn is a lot.

Personally I'd put the carburetors, and bench synchronization method, you need to return the carburetors to proper setting/baseline.

Can I ask why you needed to sync the carburetors in the first place? As my write-up states there are other causes that might be your issue, it seldom is the carburetor sync.

[Cra1g]

Originally Posted by Ghostt

A half turn is a lot.

Personally I'd put the carburetors, and bench synchronization method, you need to return the carburetors to proper setting/baseline.

Can I ask why you needed to sync the carburetors in the first place? As my write-up states there are other causes that might be your issue, it seldom is the carburetor sync.

I adjusted the valves quite a bit (they were REALLY tight), and I'm told you're supposed to do a carb sync after you adjust the valves, so that's what I'm doing (or trying to do).

[Ghostt]

As I stated you should return the carburetors to proper setting, messing with the synchronization is one of the most ill advised things done.

Reread my write-up and you'll get better understanding of why, and the true meaning of synchronization.

[Triple Jim]

I was going to say that your difficult starting symptoms point toward valves that aren't closing, but then I read that you adjusted them. It might be worth a quick compression test to verify that you don't still have a valve that's not closing.

My 250 had exactly your starting difficulties, and when I set the valves correctly, it was immediately a different, well-behaved engine.

[Cra1g]

Originally Posted by Triple Jim

I was going to say that your difficult starting symptoms point toward valves that aren't closing, but then I read that you adjusted them. It might be worth a quick compression test to verify that you don't still have a valve that's not closing.

My 250 had exactly your starting difficulties, and when I set the valves correctly, it was immediately a different, well-behaved engine.

Well, I did the valve adjustment a couple of weeks ago and the bike ran just fine. It was when I tried to sync the carbs and couldn't figure out why it was being weird when it started to act like this, so I messed something up..

[Ghostt]

Forget the compression test, you need to adjust the sync properly, until you do that any diagnostic will be meaningless.

If the bike was running fine before thought attempted the sync, then that's your problem, messing around with vacuum gauges, etc... Is pointless, a true sync is what it is, setting the throttle blades so they are the same.

I'm sure @ducatiman will chime in soon.

[Cra1g]

Originally Posted by Ghostt

Forget the compression test, you need to adjust the sync properly, until you do that any diagnostic will be meaningless.

If the bike was running fine before thought attempted the sync, then that's your problem, messing around with vacuum gauges, etc... Is pointless, a true sync is what it is, setting the throttle blades so they are the same.

I'm sure @ducatiman will chime in soon.

Alright, thanks! Another learning experience in the bag.

[Motofool]

Originally Posted by Cra1g

......... Do you think either of these things played a role?

I would first verify the vacuum hoses that you have manipulated.
Either one of the connections or tubes could be leaking air in in an erratic way.

Most times, we create new problems after manipulating things, on purpose or by accident.
Based on that idea, I would also check all the electrical connectors of the ignition circuits (mainly coil's).

If all the above results negative as main cause, I would slowly turn that synchronization screw while the engine is acting up.
You may clearly feel what direction of turning makes things worse and better.
If so, try to find a sweet spot of idling smoothness.

If you do, you can then decide whether or not continuing on with vacuum precise adjustment.
If you don't, then the source of your problems may be the previous to last thing that you have manipulated: the adjustment of the valves.
I know that the engine has been working OK after the valve's work, ..... but you never know.

Please, see:
http://www.tuneruniversity.com/blog/...-vacuum-gauge/

Originally Posted by Triple Jim

........ My 250 had exactly your starting difficulties, and when I set the valves correctly, it was immediately a different, well-behaved engine.