82 XJ750 Maxim Hitachi HSC32-12A carb synchronization

Long story. Here it goes:
Replaced fuse centre, all electrical connections on the bike unplugged cleaned greased . All good.

New Coils, wires, caps and plugs. TCI is good. Re sweat the connections just in case, I usually do this with older machines.

Complete rebuild on the carbs. Air fuel mixture screws set to the way they were found (2 1/2 turns out) (took those carbs to the "church of clean") /bench synched, Installed, No Vacuum leaks, New air filter, no holes in air box. Intake Boots and manifolds have no leaks or cracks. Started and ran reasonably well. I sprayed the intakes with wd-40 with no change in RPM. All clamps tight. All new Caps on the intake vacuum ports.

CHECKED Valve clearances. All right on the money. 30 300 Miles/48 500 Km on OD, Bike is in good shape.

Bought cheap ebay $50.00 CAD gauges with hoses that melted easily. Properly zeroed them. After 2 sets of seals used up on the YICS blanking tool, got things fairly smooth, but far from perfect. Removed carbs and re bench synched. Then repeated. Took a long time to get them close with the gauges being so cheaply made. All gauges were reading the same in the end, but they are garbage and that is where they went.

Backfiring or popping from carbs at 3000 RPM range and slightly rough idle.

It gets weird from here.

Just bought a Motion Pro SyncPRO 08-0411 Manometer . I trust manometers the best and I have been using liquid and electronic manometers for decades for calibrations on carbs and Industrial process control equipment.
The Motion Pro is easy to set up and calibrate. watched the video several times and followed the instructions diligently. If anyone has used this instrument and had success, or not, Please let me know.

Following the Haynes manual. During the synching process, for example: I synched Carbs one and two, readings were equal. Then one or the other would drift out of synch. Even if I returned the set screw to its original setting, the pair would come back to normal then drift apart. No matter how slight my turns were (were talking 1/16 to 1/32 of a turn) Giving time for things to catch up and stabilize ensuring the RPMs were around 1050.

Same with three and four. Then the readings would get MORE wonky especially when I would re insert the blanking tool, restart the engine to bring both pairs together. All four are always completely out to lunch making it impossible to bring the four together, no matter how many times I did this. I have been at this for days and went through two more sets of Blanking tool seals to give an indication of how many attempts I have given this.

I only have the Blanking tool inserted for about 30 to 45 seconds at a time, so it doesn't weld itself in there and cool it with a fan between uses.

If I take too long, I will put the YICS plug back in and run the engine to bring it up to operating temp. The Blanking tool gets lubed with silicone spray before insertion and I am extremely careful with setting the tolerances on the seals so they don't tear and seal properly. With use they wear out anyway.

I gave it my best shot by finally synching one with three while 2 and four were reading much higher readings. Still rough idle and popping at 3000 RPM range. They are far from synched. I believe this Motion Pro is a very sensitive, and accurate instrument, I still trust Manometers more than gauges. They typically never lie.
I put 312 Miles/500Km on the machine both in town and highway reaching higher RPMs to reseat things and clean things out before re attempting a synch with the motion pro.

I probably left some details out but I am reaching out and I'm open to any suggestions.

ANY SUGGESTIONS!!!! Thanks

 

This is a synopsis of using the Motion-Pro synch gauge from a long time ago (2007), so things may have changed in the design of their gauges.......MotionPro is known for making very high-quality products, but the author of this article is someone who is mechanically very adept, and isn't known for exaggerating (nor pulling punches). So with all that being said, here goes:



"As I mentioned in my previous post, Mac bought the new MotionPro non-mercury vacuum sync tool and brought it to the SOCC for testing.

We had no idea what to expect so Mac made himself the guinea pig just to provide some feedback about this mysterious new vacuum synchronization tool.

Here's what we found:

The MotionPro gauges have some sort of blue liquid in them which isn't mercury. Each of the 4 columns has it's own reservoir of blue liquid and each also has a calibration screw to bring all 4 columns into alignment. The instructions say to calibrate the tool before each use so Dwayne and Mac did just that and while calibrating discovered a strange anomaly.

It turns out that accuracy isn't a strong point for the MotionPro gauges. By applying a single vacuum source to all 4 columns for calibration, it became apparent that each column reacted differently - not equally. Dwayne & Mac would apply a certain vacuum, then calibrate all 4 columns to be perfectly aligned.

But then when the vacuum was increased, rather than seeing all 4 column levels increase in unison, each one increased at a different rate and the 4 levels went completely out of alignment. With a single vacuum source, the 4 aligned columns should have remained aligned as the vacuum increased but they diverged at different rates and ended up being dramatically different where they should have been in sync.

We examined the way the tool converts vacuum to a reading and how the calibration screws affected readings and came up with a few causes that might account for the discrepancies, each of which were somehow tied to production quality control.

But knowing that the 4 columns progressed at different rates and having some idea why they did, wasn't nearly as important as being aware that calibration would drift. What it means for others who might buy these gauges is that they can't be calibrated on a bench with an arbitrary vacuum source - they can only be calibrated on the very bike you plan to use the gauges on and at the vacuum level found in an already sync'd set of carbs.

So how do you use the gauges to sync carbs if the carbs have to already be sync'd just to calibrate the gauges before using them? Sounds like a catch 22 but it really isn't. The process would work more easily if the carbs were close to sync'd before starting but if the carbs are out of sync, it might only mean that a second (and maybe even a third) calibration might be required.

Here's an example of how things might progress (it's hard to explain but I'll do my best):

Let's assume that the carbs are horribly out of sync. Let's say 1 and 3 have far too high vacuum levels and intakes 2 & 4 are excessively low. Now let's suppose you hook the new MotionPro gauges to the excessively low #2 intake manifold for calibration. With a low input vacuum, you adjust the gauge calibration screws and bring all 4 columns into alignment about 1/6th of the way up the gauge. Then you hook things up for syncing and adjust the carb sync screws to bring the MotionPro column levels into alignment again. As you do, the vacuum levels in the carbs will start to approach equal levels, which necessarily means that the low #2 used for calibration will rise along with #4 and the high #s. 1 and 3 will drop. Although your adjustment of the carb sync screws brings the MotionPro gauge columns into alignment, you will NOT have achieved a proper sync.

The problem, as mentioned already, is that when you calibrate the gauges at a low vacuum level and then raise the vacuum level substantially, the calibration drifts and the columns end up out of alignment. As you adjust the carb sync screws and start to approach sync, the peripheral effect is that the #2 intake vacuum becomes much higher than it was at the time of calibration, which means at the new, higher level the gauges are necessarily out of calibration and that's what you're using to attempt to sync the carbs.

So as you're looking at aligned MotionPro gauges with the engine running, all you can do is put a mark at that level on the gauges just for comparison in the next stage.

Now you kill the engine, disconnect the gauges and reconnect them to the same #2 intake port for another round of calibration.

Now that the #2 vacuum is higher (after the first round of attempted syncing), you find that the columns are all out of alignment again. It looks like you've lost calibration... and you have. So you calibrate the gauges again at the new, higher vacuum level, somewhere halfway up the gauges instead of only 1/6th of the way up. It's also a good idea to mark that new calibration point on the gauges too.

Then you disconnect the calibration setup and reconnect for sync and once again, the carbs appear to be out of sync although you just thought you sync'd them. Again, you tweak the carb sync screws to bring the columns into alignment and as you do, the more equalized levels end up higher than the calibration level you just marked moments ago. Well, as long as the difference from the calibration mark to the *apparent* sync mark isn't more than about a half inch or so, you won't have to go through the cycle of calibration and sync again, but if the difference *IS* greater than that, another calibration at the new #2 intake vacuum level would be prudent

The whole thing is a function of inequalities between the four gauges. Because the 4 gauges react differently to changes in vacuum levels, you're forced to do a number of test cycles that end up like this:

a) calibrate - align columns using carb sync screws
b) calibrate - align columns using carb sync screws
c) calibrate - sync carbs

Notice I specifically wrote "align" rather than sync in the first two. That's because at that point you really haven't achieved a carb sync - you've only managed to align the columns on the MotionPro gauges and in so doing have come closer to a proper carb sync.

With each calibration and re-alignment, the spread between the calibration vacuum level and the alignment vacuum level becomes smaller. You've basically achieved sync when there's no longer a difference between the two levels.

Sounds wrong but that's how it seems to work. The MotionPro gauges are only accurate when calibrated very near the final equalized intake vacuum level. Of course, the question is how precise do you have to be?

My example was a kind of worst case scenario. In a more common scenario, you'd likely do 1 calibration *on the bike* & a single sync based on that 1 calibration.

That's what we did on Mac's bike (because his carbs had been sync'd at my place not to long before and we knew they couldn't be far off). After we were done, we verified the carb synchronization by checking the end result with a Carbtune II. The Carbtune showed a very excellent sync so we knew we were about where we wanted to be. But in reality, the Carbtune has less resolution than the MotionPro gauges so if there was a difference resulting from the calibration drift over 3/4" of gauge travel, we'd never know it using the Carbtune.

 

That's interesting - so they made a manometer, or 4 of them, that somehow allows you to calibrate the span...
The point about manometers is they are just a column of liquid, balanced against the weight of liquid in the opposite column. So how can they be wrong - or different? Sure you can callibrate the zero by moving the scale, but the range, or span, is set by the surface area of the two columns. Its all physics, basic stuff.
I suspect they have an adjustable size well, but even then you should be able to st them all the same.

 

Too much messing around. I am returning them and going back to a good quality gauge set. The video obviously is a setup. This thing is gone. Thanks for the lesson. I stand corrected.

 

I calibrated it about 8 times or more between attempts. I do not recommend this tool. Once again Thanks guys for the info

 

It is probably a good tool for other motorcycle engines. Maybe it just doesn't like the YICS engine?????????

 

Thanks again for all the Input