Carb sync lession

1985 XJ700N (airhead). According to the PO, the carbs were synched last year.

I did valve lash adjustment (all needed at least .05, couple needed .10). Then when I went to put in the YICS eliminator tool, it was plenty gunky. I don't think there has been a YICS eliminator tool in there for some time, if ever.

So I have to assume that if a carb sync was done last year, then it was done without first checking the valve lash and was done without a YICS eliminator tool.

Here's how it looked to begin with:


Not very synched, in my opinion.

Was able to dial it in though:


I have to conclude that a sync without a valve lash adjustment and without a YICS tool is not going to be effective. Everybody says "do the valves first" - I guess this is why.

 

YICS tool is not needed. The end result will be the same.

 

+1

Never used the YICS blocking tool and have a wonderful synch.

 

Is it normal that the sync readings are that low? Mine read somewhere around 20 I believe (not sure but definitely higher). Or can that be the result of not fully closing valves?

 

Nice job and I also believe the YICS tool is not needed.

 

What's shown in the OP's second pic is normal for bikes with the YICS system. Your X does not have that.

 

Maybe I should throw the gauges on without the YICS tool in place and see if it makes any difference. You know, for science.

 

So assuming the carbs were synched last year (may or may not be true), and if the YICS tool doesn't matter, can the valve adjustment affect the sync that much?

 

https://www.xjbikes.com/forums/threads/yikes-all-about-the-yics-system.14757

To review:

According to Yamaha, the function of YICS is to promote more complete combustion at low to mid-range rpm by swirling the mixture around the combustion chamber. They never made any direct power claims -- the system was promoted as increasing mileage up to 10 percent and promoting lower emissions through a cleaner burning charge. The increase in mileage was not through leaning out the mixture -- the increase in mileage and reduction in emissions was because less throttle was required to maintain cruising speed. They could use the same cam timing, jetting, etc. (for performance) and still meet EPA regulations. Yamaha stated that the greatest effect was while cruising at 50 to 60 mph.

The swirling accomplishes two tasks: first, it assists mechanically in atomization of the fuel and second it speeds and distributes the flame front (and therefore combustion pressure wave) more evenly throughout the cylinder. The later "Genesis" (water-cooled "X" engines) design accomplished this even more effectively through the 5-valve design, which accomplishes the same task through a much wider rpm range.


To blank or not to blank (during engine synch), that is the question.

Ok, what is the function of synchronizing? Manufacturing tolerances and wear. Multiple carbs offer the advantage of increased power and performance over the single carb configuration for reasons beyond the scope of this discussion. But at a cost.....

As each carb is dealing with a fraction of the total air and fuel flow requirement, each carb must meter things in fractions of the total. That makes for some very tiny tolerances. In effect, we have 4 separate engines -- if one is fighting the others, then we are wasting power and fuel and are worse off than we would be with a single-carb setup! So it is crucial that each one be perfectly adjusted and that all 4 then be synchronized to work in perfect harmony.

So, how can we reliably adjust an individual carb based on the results of the adjustments, if it's companions are contributing to the results?

Now, to be fair-----if the bike has been reasonably well maintained and the cylinders are all fairly close to begin with, you can usually get away without blanking the YICS passage and still achieve a reasonable state of tune. At the opposite end of the maintenance spectrum, the YICS passages are often already plugged up with many years worth of accumulated grunge and grime, so the bike is effectively being tuned with the YICS system disabled and the presence of the tool is irrelevant. But we have seen some examples of carbs where one cylinder was effectively relying on its neighbors to supply most of the mixture through the YICS system, and this most certainly affects performance, especially the top end.

Take a look for yourself:




So, the recommendation is: for an engine with approximately equal compression across the cylinders and valve clearances in spec, make sure the YICS passages are clean and use the blanking tool to tune the carbs.



The most important point to remember:

The pronunciation of "YICS" is "yiks", not "yikes!", no matter what anyone else tells you!

 

You are not understanding the entire process correctly, which is understandable since the words that people typically use create and add to the confusion.

You can most certainly synch an engine (note, and this is vitally important, if you don't understand the following statement, you'll never be able to understand the entire process, what you're doing, nor why you are doing it): you don't (do NOT) synch the carbs, you synch the engine......and you synch the the engine via certain adjustments to each carb (basically, adjusting the openings of the throttle plates on each individual carb). Period. Full-stop. Understand that, and the world's your oyster. Overlook that point, and you'll be lost in a world of mirrors and misunderstandings, forever.


https://www.xjbikes.com/forums/threads/82-xj-650-startng-problem-surpise.46358/page-2#post-414262

Not wanting to be a killjoy and interrupt this Thread-Of-Happiness, but I feel that, for clarification purposes and---in tribute to the immortal words spoken in the classic, epic, pre-salad-dressing days of yore in "Cool Hand Luke" by Mr. Paul Newman---it should be said that in assisting in "Getting your mind right" I should gently point out that an oft-repeated statement expressed 'round these parts isn't quite the truth, the whole truth, and nothing-but-the-truth, and that statement is this:

And yes, I know that this gospel comes straight from the red-circled horse's mouth, Yamaha Motor Company.

But it ain't true, and it begins with the reality that you ain't "synching" the carbs, at all, no, nein, nyet, nope.

You're synching the engine via the adjustment (of the throttle shaft openings) of the carbs.

And I'm not just trying to nit-pick words; words have meaning, or, as a former president of Ford Motor Company used to say, "When I speak, each word weighs a ton". Words convey an understanding of what is going on, and the wrong words give a person the wrong understanding, the wrong visual, the wrong (in modern hipster slang) "optics" in their minds, and a wrong understanding of what is going on (and what you need to do to correct it), and can easily turn a mind into that dreaded "terrible thing that's been wasted".


http://dictionary.reference.com/browse/synchronize?s=t

Synchronize: to cause to go on, move, operate, work, etc., at the same rate and exactly together: They synchronized their steps and walked on together.


Does setting all the carb openings to differing amounts mean that they "move, operate, work, etc. at the same rate and exactly together"?

Well golly-gee no, it doesn't. In fact, the process of "synching" does EXACTLY THE OPPOSITE, in regards to the carbs........it sets them up to "operate" slightly differently from each other. On purpose.


For what purpose, you may ask? For a good purpose, of course! So that you can equalize the power output of the cylinders, so that you can "synchronize" the horsepower/torque output of each cylinder, so that each cylinder will, in fact, "work, etc. at the same rate" (or power output).

And by the way, for you guys that are over-edumacated, you'll immediately recognize that the word "work", in this context, is really close to the physics definition of "work", that being of energy output over a unit of time. But I digress.......


Having each cylinder output 20 horsepower (20-20-20-20), rather than a cylinder power output map that looks like this: 16-23-24-17 ----- and please notice that in both cases, the total engine output is 80 horsepower ---- but in the 2nd example, since each cylinder outputs a different amount of power, the engine will "fight itself" and run rough, perhaps misfire, beat itself to death, etc. Definitely not that "sewing machine smoothness" that we all adore and aspire to.

And beat itself to death, over time, it surely will. Having grossly mis-matched power outputs in each cylinder puts incredible stresses on the crank, rods, and bearings. If that thought doesn't bother you much, then do the following:

a) carefully remove your valve cover. Set all the bolts aside, labeling as necessary so you can re-assemble properly.

b) remove the camshaft bearing caps, just one or two of them. Again, put aside and label.

c) get your ball-peen or claw hammer out, and start hammering away, as hard and as fast as you can, on the cam journals. Try to do this at least 3000 - 6000 times a minute to closely duplicate what an unbalanced engine does to its rod and main bearings.

d) re-assemble everything and go ride your bike in traffic, or on a long-distance ride. It's all okay. These engines are built tough.


Now, why would an engine have a power output map of something kooky like 16-23-24-17, or even 19-21-22-18 (note this last one is a lot closer to being equal across each cylinder). Well, it could be that the pistons/rings in each cylinder aren't EXACTLY equal in condition to each other. Maybe one cylinder has a bore that is .02mm larger than the others, or maybe a larger ring gap on the top ring. Or another cylinder has a valve that isn't seating/sealing as well as the others.

Or, hey, how about this: all of the valves ARE in spec, but since spec is .11-.15mm clearance (on the intakes), suppose cylinder #2 intake valve is at .11mm clearance and cylinder #4 is at .15mm.....both within spec!......but the different clearances results in different valve timing (when the valve opens and closes within the cycle) and thus a different power output from each cylinder.


What you want is a power output of 20-20-20-20, or at least as close to that ideal as possible.....and note that it MAY NOT BE POSSIBLE. Cylinder #1 has a slightly.....which is well within tolerance, mind you.....larger bore than all the others. It has a little bit more ring blow-by. It won't/can't develop as much compression pressure as the other three. So you get compression numbers like this: 131-133-139 -137

Again, well within "spec". But cylinder #1 isn't going to EVER make as much power as the others, and short of taking the engine apart and "blueprinting" it, that "little #1 cylinder that could" well, in reality it couldn't, wouldn't, and it won't ever make as much power as the other cylinders.


So note that the "synch" process forces you ---- via adjustment of the carb throttle shaft openings, setting them all a little bit differently from each other ---- TO DE-TUNE THE POWER OUTPUT OF 3 CYLINDERS DOWN TO THE LOWEST COMMON DENOMINATOR LEVEL.......it's the educational system equivalent of "dumbing down" the students so that everyone gets a gold star.....

So in this engine: 16-23-24-17

you're going to have to "de-tune" each cylinder to 16hp, so that it ends up looking like this: 16-16-16-16


But in this engine: 19-21-22-18

you'll be able to achieve this output map: 18-18-18-18


Hey, that's an extra 8hp, which is nothing to sneeze at in an engine of this size, and truly a difference that you can feel.....


So why do you adjust the valves (or: set the fuel levels? or: set the mixture screws?) before you "synch" (really, un-synch) the carbs? Because out-of-spec valve clearances will typically get you this engine:

16-24-24-17 (which you can then "synch" to 16-16-16-16)

while valve clearances in-spec will allow you to get this result:

19-21-19-21 (which you can then "synch" to 19-19-19-19).


Look, you can't do anything about cylinder bores, ring clearances, valve seat seal, carbon build-up, etc. as part of any normal maintenance procedure (well, you could, but 99.99% of people aren't going to do a top-end job every 5000 miles). But you can adjust your valve clearances pretty easy. And doing so will allow you to flash a big toothy grin with "19's" all across the board, rather than a set of 16's on all cylinders, and unlike what you read on the internets, the "size" of numbers does matter, and bigger really is better-er.


So in conclusion: Yes, Virginia, you can "synch" even if your valves (or fuel levels, or pilot circuit fuel mixtures, etc.) are not in spec ---- you can synch your engine to 16-16-16-16 instead of 20-20-20-20 ---- and negate lots of the fine engineering that Yamaha did for you and piss away 16 horsepower the fast and easy way.

Like they say on TV, it's your dime, Boss............

 

Best explanation yet...well done sir!

 

I've read your explanation before, it was an eye opener! You're really the master in explaining!

 

If the valves aren't in spec there is no point in synching the carbs. Not because the carbs won;t be in synch, but because the synch will change when the valve are adjusted.
Each change in a system of systems changes the other parts of the system.

 

Loved the write-up. I've always thought the idea was to balance the cylinders by adjusting the carbs.
By the way, how do you make sure the little opening in the YIKS channel are cleaned and not clogged? Cleaning the main passage seems straight forward enough, but what happens if one of more of the small opening gets clogged?

 

We have a special little tool with a sharp "pick" (pointed tip) that is the proper size and depth to reach the ports.......you can use a bent paperclip or the like, but it takes a bit of leverage under it to punch thru the gunk that clogs those tiny ports in the top of the chamber, as the crud that blocks them gets coked (hard carbon) pretty well over the years.

 

In the video you posted I saw only 2 ports in the top of the channel. I assumed that there were 4.

 

There are 4 ports, one for each cylinder, in the video, I believe he only pushed the camera halfway thru (or maybe it was some other engine).

 

I used welding wire and a screwdriver that fits the opening. Pics attached.

 

Yep,, that will work!

 

Thanks. I thought there were four. I have welding wire and a bunch of screwdrivers, so that will work for me.