A journey through a hanging idle.

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.