Messing with the screws

[Guest]

Ken posed this question on another post. Rather than hijacking the post, I decided to open another.

"I could be wrong and often am but wouldn't out of sync carbs affect low end performance not top end?"

The biggest mistake one can make is assuming the guy who worked on it before you, knew what he was doing. More often than not, many "mechanics" adjust around a problem, instead of fixing it. I've seen a lot of threads that suggest adjusting carbs at 3,000 rpm, because that's where we do all our driving. Unfortunately, if the carbs are sync'd at idle, and they're not at three grand, there's a problem with the carbs. Bad slides, sticky slides, ruptured diaphragms, vacuum leaks, etc.
That's the second biggest reason for bringing the rpm's to 3,000 during a carb sync. If they pull together at idle, they should pull together at 3,000 rpm.
Sync the carbs correctly. There should be relatively little difference between idle sync and 3 grand. If there is, the carbs need to be gone through.

It's quite possible, especially on a new addition, that someone has been "fiddling" with just about every adjustment possible to correct a driveability concern. Beware.

[Guest]

Isn't that what I said?
Syncing the carbs lets equal air/fuel flow to each cylinder at idle.
At part throttle inequities maybe evident but at full throttle unless there is something wrong with the linkage where by the throttle plates are not moving together the diaphragms take over control of the slides.

In my humble opinion syncing the carbs will not improve top end performance noticeably.

Ken

[Guest]

The diapragms don't "take over control". The diaphrams are acted upon by manifold vacuum. The amount of vacuum applied to the diaphragms is directly related to throttle position. The same throttle plates that are adjusted during syncronization. If the plates are out at idle, there will be unequal vacuum applied to the diaphrams at higher rpm as well.

[Guest]

I've been thinking and thinking and your right about the manifold vacuum. :oops:

However I still believe my origanal post on the other thread was correct.

Miss-alignment of the throttle plates by a few degrees will cause problems at low throttle settings but once you open them fully the same few degrees of miss-alignment will not affect the air flow or vacuum enough to notice.

From the origanal thread.

it will pull good until around 4000 rpm at which point it begins to run rough and not pull as hard any more.

Which as you suggested could be ignition related but could also be bad diaphragms.

Ken

[Guest]

I think you missed the point, Ken. If all circuits are clean, diaphragms are good, spark and compression correct and the carbs sync'd correctly, there would be zero affect at 4,000. In this case the answer to your question would be "no". Syncronizing would not affect high end.
Let's assume that one of the idle circuits were partially plugged. If you sync the carbs at idle, you would have to effectively open the throttle valve to allow more vacuum to work on the carb and thereby "balance" the carbs. Since the carbs are linked mechanically, the farthest open the throttle plates can travel is limited by the throttle plate that hits the stop first. In this case, the other three wouldn't be allowed to open fully and top end performance would be affected.
The real point I'm trying to make, is that when you get a "new to you" bike, you can't assume anything. Many driveability complaints may have been "masked" by someone "messing with the screws".

[Guest]

Glhonda,

Thanks for the input.

I have been riding my bike for about 2 years now. At the beginning of the first year, I sync’d the carbs according to the manual. I got them balanced at idle but there was about 1” difference between the mid-range to high and low readings, ie, 2 inch difference overall.

What is an acceptable variance between the mid-range reading and the high and low readings?

Recently, my gas mileage has been going down so I think it’s time for a new sync job and plug replacement. I have done about 10,000 miles on the 1st set of plugs over the two years. So they are due for a change. Are iridium plugs worth the cost?

I have not found any information regarding this subject.

Thanks,

[Guest]

Mike, I think your missing something important here.

Yes linkage out of adjustment can affect performance at all throttle settings but if you synchronize the carburetors at idle barring problems with the linkage they are synchronized throughout their whole range.

Next let's look at what synchronizing is.
It's basically setting all four throttle plates at the same angle to get the same air flow/vacuum in each manifold, it matters not if one, two, three, or four carburetors are running the engine, heck you could even get a gorilla with a wrench to spin the engine up to speed, synchronize the carburetors then adjust the idle speed when you do get it running.

Ken

[Guest]

Sorry Ken, I have to disagree.
When you sync the carbs, you are not putting all the throttle plates at the same deflection. You are adjusting the throttle plates to obtain the same "vacuum" on all cylinders. If you have a partially plugged idle circuit, or poor compression, or poor spark, or leaking valves........then the plate for that cylinder will almost certainly need to open wider than the rest to obtain the same vacuum as a healthy cylinder. In that case, your theory is my theory. Since the plates are linked mechanically, barring any linkage issues, the plates will be "off" the entire range of operation. Syncing the carbs at idle compensates for "idle" annomolies. But can affect upper end performance as well.
As far as your gorilla theory goes.............I've worked behind a lot of gorillas. Trust me, they can't get an engine running. :lol:

Owaace...there is no documentation that I know of for midrange or high end vacuum readings. All information for most multiple carb bikes have the manufacturers agreeing to around one inch of hg difference at idle.
When I sync my carbs, I run them to 3,000 rpm. TO CLEAR OUT THE CYLINDERS. If you think I'm shouting, it's because I am. You will not find a spec for vacuum at three grand. You need to clear the cylinders to recheck your base adjustments. Messing with the screws causes the cylinders to load slightly, and they need to be cleared for optimum results.
I put my vacuum dead on even, with no discrepancies between cylinders. Raise it to three grand and then check to see if they are still on. If they aren't, it's a good indication that something is amiss. It should also help to tell you what cylinder it is. At 3,000 rpm I would allow that 1"hg difference the factory specifies. If someone finds something in print from a manufacturer that states different, let us know.

[Guest]

Mike, I can agree with

If you have poor compression, or leaking valves.

but if the engine is in good condition mechanically and a compression test will tell the story, poor spark and/or plugged idle circuits will not affect synchronization of the carburetors other than requiring all four throttle valves to be opened more and equally to compensate for the cylinder that is not carrying it's weight.

Also

When I sync my carbs, I run them to 3,000 rpm. TO CLEAR OUT THE CYLINDERS.

I have to disagree there to. Your just opening the throttle to release any stresses you put on the linkage by playing with the screws and of course to clear out the cylinders in order to get a proper idle speed but loading up of the cylinders will not affect the actual synchronization of the carburetors.

Ken

By the way you've probably figured out that I'm opinionated but I came by that honestly, I inherited it from my dad God rest his soul and that I chew on a bone until I get to the marrow. :d

[Guest]

poor spark and/or plugged idle circuits will not affect synchronization of the carburetors other than requiring all four throttle valves to be opened more and equally to compensate for the cylinder that is not carrying it's weight.but loading up of the cylinders will not affect the actual synchronization of the carburetors

I'm beginning to get the impression that you haven't sync'd very many carbs.
Maybe it's the terminology that throws some people. Syncronizing. Not really the best explanation of the process. "Balancing" is the term to use.
Four vacuum readings, four carbs, all linked mechanically. What you do to one, affects the rest. You don't have one vacuum reading. You have four separate and distinct vacuum readings that need to be equal or "balanced" for smooth engine operation. You don't open all four throttle valves equally, you open each individual valve until the cylinders are balanced. The plates are not going to be open an equal amount, especially if you have a problem cylinder.

[Granpah]

Maybe it's the terminology that throws some people. Syncronizing. Not really the best explanation of the process. "Balancing" is the term to use.

I was having a great time following this debate until out popped the above. I'm (partly) a writer, so let's see if we can clarify a couple of terms.

As I understand it, all GL1200s have four separate (independently operating?) carburetors -- that are mechanically linked (once linked they're no longer "independent"). So then getting them to work efficiently in "tandem" (one behind the other), each one must be optimized (performing at the same level) and also equalized (more about this below) as the rest. In this case, "synchronizing" means nothing more than each carb producing the same measured vacuum reading on the four independently connected gauges. But K. Bergen wishes to call this "balancing".

Assuming the elecronics are equal for each of the four cylinders and the ignition timing is perfect, I suppose that performance is limited by synchronization/equalization and how the carbs are linked.

K. Bergen wrote: "You have four separate and distinct vacuum readings that need to be equal or "balanced" for smooth engine operation."

I'd say, rather than balanced, when all four vacuum readings are equal, they're literally "equalized". So then rather than saying "synchronizing" the carbs we should say equalizing the carbs because the equal gauge readings are used as the endpoint for concluding that the carbs are operating in tandem as they were originally designed to operate by Honda.

So far as the RPMs at which the carbs are equalized, what does the manufacturer use as the standard? I think someone here quoted 1,000 RPM. But Ken's point is well taken that the carbs should be optimized for the RPMs at which they mainly operate (rather than at which they idle).

'Hope I haven't muddied the waters too much.

Still, I do understand the above drift and ALL of it is valuable.

Thanks fellas.

[Guest]

Well, Granpah, you misquoted both myself and Ken. You can call it balancing, you can call it syncronizing, you can call it equalizing. It's all symantics.
The manufacturer gives specs for idle.
If you have to balance, equalize, or sync at a higher rpm, you have a problem that should be fixed. High sync only masks a concern, it doesn't fix it.

[Guest]

Well, Granpah, you misquoted both myself and Ken. You can call it balancing, you can call it syncronizing, you can call it equalizing. It's all symantics.
The manufacturer gives specs for idle.
If you have to balance, equalize, or sync at a higher rpm, you have a problem that should be fixed. High sync only masks a concern, it doesn't fix it.

Agreed, if the vacuum readings change significantly relative to each other at higher RPMs then you have a mechanical problem, either with compression in the engine or something is wrong with the linkage.

Ken

[roscoepc]

As I understand it, all GL1200s have four separate (independently operating?) carburetors

A quick comment to further "de-muddify" the waters.. Not all gl1200's have carburator's. The '85 Ltd Ed and the 86 Aspy SEi are both equipped with computerised fuel injection. The only "balancing" adjustment is on the throttle linkage is side to side so only 2 manometers instead of 4 are needed. There is no front to rear adjustment on the injectors.

[admin]

To add to the confusion, there is an adjustment to the front and rear throttle plates on the injected bikes, it is called cleaning. Sometimes the throttle bores can become so gummed up that the accumulation will affect the synchronyzation noticably. Carburetor cleaner sprayed into the throttle bores with the throttle blades open will normally clean out the debris and restore good running and proper balance and raise the idle speed.