A journey through a hanging idle.

Well, it's easy enough to test for someone with a stock YICS bike and the tool: balance it with the tool, then pull the tool out and check balance. If my theory is correct, it will still be balanced. If your theory is correct, it will shift.

 

That's well worth looking into.

 

Absolutely true, but Chacal's point about the ports potential to get clogged is accurate; the issue is a matter of when. The YICS ports don't just get clean fuel/air mix. They also get some of the exhaust blowback during overlap, and some of the vented air from the crankcase (via the air box). Personaly I would not expect much carbon buildup in a properly tuned engine (using mine as the only baseline I have), but I can see the potential for carbon buildup blocking the ports if one or more cylinders are running rich for an extended period of time, if the rings are worn (resulting in elevated blowby), or an intake valve is not fully sealing. Given how often valve clearnaces are left go I'd be inclined to think that the latter scenario is fairly common.

 

let's put a "what if" in here. Tool in, carbs sync'd, idle smooth. What if, tool comes out, carbs still sync'd, idle still smooth......what did the tool do, carbs are sync'd either way, idle is smooth either way.
Now, tool in carbs sync'd, idle smooth. Tool comes out, sync changes, idle is rough. Where do we go from here?
re-sync without the tool
clean the 3mm ports by pushing the crud back up the yics port and hope it stays there.
pull the carbs and spray carb cleaner down the yics port to try and rinse it out
pull the head and get a new head gasket
maybe push the crud up then rinse might be the way to go. or just forget the tool

 

Here's some more YICS information

http://www.xs11.com/forum/showthread.php?t=35619

Dave F

 

One other thing in regards to a hanging idle; make sure the throttle cable and throttle tube are clean, lubricated and in good working condition. A sticky throttle cable or tube can prevent the throttle plates from fully closing.

Another thought about the YICS system. Consider that it is an emissions device. Could it not be that the only discernable difference between using the tool and not, would be seen as enough of a change in emissions to meet EPA specs for the era? Who has a gas analyzer?

 

The purposes...advertised or in reality....of the YICS system was to enhance fuel economy. Since almost nothing else changed between the non-YICS and YICS versions of the engines (at least in the 650 engines, the only one where a meaningful before-and-after comparison can be done), I think it's pretty safe to say that Yamaha wouldn't have done it unless it "made a difference". The only way to get better fuel mileage from an otherwise-identical engine/bike/powertrain is either via:

a) better use of the fuel introduced (i.e. more efficient use of the fuel thrown into the combustion chamber), or.....
b) less fuel being introduced, and just live-and-let-die with the results of running a continually-lean, air-cooled engine.

Perhaps "b" is the approach that Yamaha chose, bit I doubt it.

The YICS system is clever, it uses no moving parts, and simply works off the internal physics of engine design. Honda (the car) used a similar type of system back in the late 70's with their CVCC engines, so it wasn't really a "flash of brilliance" on the part of Yamaha, rather (my opinion) the creative adaptation of a known and PROVEN method of achieving the goal.

These 4-cylinder/4-carb engines are, in essence, 4 different engines ganged together via a common crankshaft. As such, 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 ---via the common, shared YICS passage --- are also contributing to the results?

I leave it to greater minds than mine to answer this burning question!

 

The way I understand it, there would be two occurences where using or not using the YICS wouldn't make any difference:

1-all passages are 100 % blocked so carbs can't suck any air except thru their own throat

2-every carb sucks exactly the same threw its venturi AND all passages allow exactly the same amount of air to flow.

THe first event is very much more probable to occur with our old bikes.

This said, considering the diameter of the YICS passages compared to the venturi, what percentage of the total amount of air sucked in thru each carb would it mean? 5% ? less?

 

sorry, sent the message twice and don't know how to erase completely

 

I recall a discussion about backfires. Non-YICS engines have a tendency to backfire during engine braking whereas YICS engines do not have this tendency.

Anyone else remember this discussion?

 

Wow, lots of information in here over the past few days.

K-Moe. Yes, my carbs were aligned properly on a thick piece of glass when I put them back together. When they're off the bike, they do slam back down, with the vigor of a mousetrap.

Dragsta: Tank is not stock, and petcock is completely gravity fed. #3 vacuum has been plugged.

Let me ask you folks this: Has anyone found cheap solutions for Vacuum port plugs? Though I haven't done the propane test yet (Waiting to set fuel levels before putting the carbs on the bike).

Since I'm setting the fuel levels, I figured I might as well start over since I do have the colortune and know that my jetting should be sufficient (though I'm going to order some extra sizes to have handy for the future). Went ahead and E-mailed hogfiddles to get one new valve shim while I have the valve cover and tank off and am learning to properly set the floats for the fuel levels.

I'm having a difficult time figuring out if my fuel level setup is correct. Does my tubing position look correct? Because you can see a small mark I made on the carb, 3mm from below the lip of the carb (marked while bowl still attached to carb body), and you can see that the fuel level in this tube/carb is quite a bit below it. I think I've got the hang of how to do it properly thanks to the DIY but just wanted to check if the procedure looks right before I start bending the tang.



Thanks.

 

Your setup is good. Your local autoparts store has vacuum port plugs.

 

you should stop right now and take all that gas and carbs and rags with gas outside before you launch yourself over to Lawrenceville.

 

test the level of carb 1 against carb 4 to insure left right level.
I do see a fire extingusher in the back ground as well as a radio controlled airplane.

 

..and a natural-gas furnace.......

and a shop vac, and a great big likker bottle like grandpapy used.

 

YOu should not have an air bubble in the test tube. I'm not sure, but I think there is one in yours, it'S hard to tell on your first picture

 

Your set-up and method is exactly correct, the fuel level is way too low (will run lean).

 

Thanks for the input guys, and good eyes all around. As for the natgas furnace concern: I have two rather large and powerful fans blowing out the door when I'm using flammable chemicals, and have an extinguisher as well. Caused me no issues last winter. That said, The most gas I've had in the basement was just enough to complete this exact process and or start the bike.

Luckily the furnace isn't even on yet...but that'll change shortly

 

Len can you explain? Thanks

 

I used blue windshield washer fluid to check the bowl levels on the bench. No smell and no danger. Downside is flushing it all out when you are finished.

 

Fuel level (bottom of the fluid surface, not the curved up edge) should be 3mm +/- 1mm from the edge of the carb body (gasket face). Yours looks lower than that.

Also, while the slides should drop smoothly and "clunk", they should free-fall. For instance, on my Virago, I had once carb where the slide dropped instantly, and the other one was noticeably slower. I thought the slower one had a problem, but, in fact, it didn't - the diaphragm had broken loose from the slide in the instant-drop one.

 

The bigger downside is a significant difference in specific gravity. Recheck and you'll find that your fuel levels aren't the same as they would be when using gasoline.

 

The clunk test is normally done with the carb hat removed so the diaphragm is not in operation. This also makes it easier to perform the test while polishing the slide (if needed) without having to fully reassemble each time.

 

Well, as with most things relating to the bottom of the carbs, things are "backwards". The physical fuel level is TOO LOW in the bowl, thus the fuel LEVEL MEASUREMENT will be too LARGE (a higher number), since the MEASUREMENT is done from the base of the carb body (where the bowl snugs up into the bottom of the carb base).

LOW physical fuel level in the bowl = HIGH fuel level measurement (lots of distance between top of bowl and level of fuel)
HIGH physical fuel level in the bowl = LOW fuel level measurement (not much distance between top of bowl and level of fuel)

A LOW physical fuel level in the bowl (= a HIGH fuel level measurement or distance) means that for any given amount of venturi vacuum available (acting upon the fuel), some of that vacuum energy is going to be used to suck the fuel up a GREATER DISTANCE than the fuel system designers had in mind.......thus not as much fuel will be made available to the main or pilot fuel circuits = a lean condition.

 

The phrase "from the gasket surface" confuses me. Therefore I've taken pictures of several possible ways that myself (or anyone) could interpret that. Disregard the very sloppy "3mm" I measured with a sharpie on the business card. In doing the procedure I'll be more precise.

1.) the way shown in above posts where I measured 3mm below the top edge of a business card, and simply placed it against where the carbs meet the bowl while the bowl is assembled

2.) with the bowl off, at the top of the gasket surface

3.) At this point, whatever you may call it (could potentially be same distance as option 1)

4.) By taking bowl off and measuring from behing the lip where the top of the bowl would mate within the lip of the carb body (this could potentially be the same measurement as option 2).


And for good measure, here are two videos: One is how my slides will slide with the carb hats on (slower, and not very clunky due to the vacuum).


The other I have titled "mousetrap vigor"

 

the first picture is right, the clunk looks good and the throttles sound right. Now note the butterflies after you snap them, then try closing them very slowly and see if they stop the same place

 

I tried that and it just plain and simply did not work because gas and washer fluid are different specific gravity properties

 

I don't believe that the first pix is quite right.......my understanding is the 3mm is measured from the bottom (base) of the carb body WHERE THE BOWL GASKET WOULD SIT (but w/o the gasket in place). That's about an extra 1mm or so in "depth" up into the body. The small "lip" or flange on the base of the carb body overhangs the face where the bowl gasket would sit.

Pix #4 is correct, and pix #2 is close except for the fact the the gasket gets squeezed a bit thinner when it is installed (screws) onto the body, so it's not quite as precise a measurement.

Pix 2 would be the same as Pix 4 if you removed the bowl gasket and measured off the top flat face of the bowl.


EDIT: I screwed up, Polock is right (as usual) and Pix #1 is correct!!

 

I've always measured like pic #1.

Gary H.

 

Me too; based on the float height measurement being made from the bottom of the carb body (the gasket surface) as well.

 

Thanks for the help guys. I agree dragsta that all of a sudden I'm running lean and not firing in one cylinder is interesting and probably not related to the float bowls. But mind you that it is only carb 3 starving for fuel. All other plugs are sooty. I figured, if I'm going to diagnose this properly, what the hell, might as well do a tune up (Valves, Floats Set, Sync, Colortune) just to get that out of the way before putting it away for winter.

I'm hoping to have a new valve shim in this week and my fuel levels set today. If that's the case then I'll be able to button everything up on Saturday and give it a vac sync and colortune while also checking for vac leaks.

Also, I've read that both Kawasaki and Yamaha Use 29mm valve shims but it appears that Yamaha uses the Y280 (for example) but Kawasaki uses 2.80

Is that simply a designation for manufacturers? Because I have a Kawi Shop nearby with a 2.80mm shim

 

Just keep in mind that soot is due to INCOMPLETE COMBUSTION, which does NOT always mean "too rich". A far too-lean mixture can cause intermittent firing, which also typically results in incomplete combustion, and can soot up the plugs (and everything else int here, too!).

You have the right attitude and the right plan. Keep us posted on your progress!

 

haynes manual for wet set 750 this is also how my yamaha fsm shows for a 550

 

Is the in-line filter a cone shaped sintered filter?

Gary H.

 

Rocs, yes it is. Plenty of fuel flow from the tank to the carbs. I went ahead and picked up a 29mm kawasaki valve shim that, despite having a different marking on it, was exactly one step up from my Y275, effectively making it a 280 (checked with digital caliper).

I also picked up new NGK BP7ES spark plugs since A.) the bike was running "Autolite 63" spark plugs and B.) The spark plug in cylinder 3 (the problem cylinder here) had a chip missing from the ceramic

This might be a stupid question, but Chacal, are these the feelers I purchased from you? Im having an "Oh crap" moment where I'm wondering if I used the wrong ones and or denominations.



To measure the valves and the spark plug gap, I', using the bottom denomination in MM correct?

If not...I've got a lot of measuring to do.

 

Correct.

Gary H.

 

Hey Brosef, I don't think that you bought those from us, although they do look a lot like our HCP6383 feelers:

HCP6383 Aftermarket METRIC FEELER GAUGES SET. These gauges will work on all XJ engines including the XJ700-X and XJ750-X water-cooled models, which require narrower blade-tip feeler gauges to check the intake valve clearances on those models. Aftermarket 32-blade metric set has 95mm long blades, hardened and polished, with the thin, tapered ends needed to access the valves on these models. Marked in both metric and decimal equivalents, as listed below. NOTE:: these feeler gauges will fit perfectly, although you will have to rotate the blade 90 degrees to the holder for some of the inner valves on X-models.

Comment: the inclusion of inch measurements AND the inclusion of smaller sizes makes this set ideal for all XJ-bikes and especially for X-models.

X-engines have valve clearances in a range from .004" - .012" (0.11 mm - .30 mm)

Decimal Inch Sizes:

.001, .0015, .002, .0025, .0028, .003, .0035, .004, .005, .006, .007, .008, .009,
.010, .011, .012, .013, .014, .015, .016, .018, .020, .022, .024, .025, .026, .028,
.030, .032, .034, .035, .040"

Metric millimeter sizes:

.03, .04, .05, .06, .07, .08, .09, .10, .11, .13, .15, .18, .20, .23, .25, .28, .30,
.33, .35, .38, .40, .45, .50, .55, .60, .63, .65, .70, .75, .80, .85, .90. 1.00mm

 

Hmmm....

Then was it these? Im complicating things I know, but I'm certain one of the two came from you. Regardless, I just wanted to check that I'm using the proper metric measurements.




Also, as I've been setting the fuel levels just now, I noticed this:

Here's a video of the fuel draining from carb 4 with a flowing fuel source (notice how quickly it drains?):



And below we have the carb three (The problem carb that wasn't firing) draining. Notice how much the flow seems to be impeded compared to four:



Have we found the culprit?!

Taking it apart as I type (almost)

 

I don't see any video, just two black squares.

 

float needles stuck opened is pretty common.

 

If the float needle was stuck open in carb three, it would have normal fuel flow when draining the carb, (like my 1,2,4 carbs do), no? But since it is the problem carb (white spark plug, cylinder not firing) while all others are dark and running, I couldn't help but make an observation. Hopefully the embedded videos work, they do for me.

 

notice on the fast one how the gas fills the tube. not so on the slow one. once the tube is full and the gas starts falling it pulls the rest of the gas in the bowl out. the slow one just drains as fast as it can come through the little hole in the carb bowl. is that technically a siphon?
at first when i looked at the first picture of the feeler gauges i thought they were a foot long.....no more beer for me

 

My first thought would be : how fast a bowl empties depends just on the drain passage itself, it has nothing to do with the float itself. But , if a bowl is almost empty when you open the drain screw (float set way too low), it is possible the flow will be weaker.

 

Valve clearances correct, fuel levels correct, new NGK spark plugs. Put everything back together as it should be.

Started up and same ordeal (granted I have only bench synced). 1,2,4 cylinders warm after a short idle. Still nothing from three. I've also sprayed propane all over the place with no change in RPM.

 

Try turning on the choke a little bit and seem if #3 comes to life I.e. exhaust pipe warm up).

 

Possible bent slide spring creating no lift at #3? Switch the vac hose to another carb and cap #3. Any change?

Gary H.

 

Hopefully the choke brings it to life as Len suggested. However, probably a good time to do as SQLGuy suggested and check compression on that cylinder just to rule out any internal damage.

 

Will try choke later today.

Brand new plugs in the bike, so fouling is out. Bent slide spring is most likely out as well, since all slides have the same amount of "fall speed" when assembled.

Also, I don't have a vacuum hose (all ports are blocked off), as the petcock on my fuel tank is gravity fed.

Ahhh keep those suggestions coming gents. At some point I'll post another summary of where I'm at/what I've tried up to this point.

 

All spark plugs have spark.

I went and bought a compression tester from Harbor freight. This one to be exact:



I proceeded to take all spark plugs out and use the hose and 14mm attachment. With the engine only warned up for like 90 seconds max, throttle wide open, the pressure I was getting was, from 1 to 4: 50, 52, 55, 60.

Figured that couldn't be right...that's way too low for the engine to run.

I then switched to the straight rod fitting that basically presses into the spark plug hole and seals by force.

Cylinder 1 was 112, cylinder 2 was 118, cylinder 4 was 112, and then when I went to cylinder 3 (problem cylinder) it went to 70 psi and then the pressure gauge broke. Sooooo basically a waste of a trip and 25 dollars.

But the initial low readings were all in line, couldn't I assume for the time being (until I can buy a better tester) that they are all in good shape?

 

A gauge that does not give consistent readings (you should have gotten similar values no matter which adapter you used) can not be relied on to tell you anything of value.