*UPDATED* Weak spark on #2 CYLINDER

I see what you're saying with the float level now. I had it in my head that the float doesn't affect things that much. I will talk to chacal and get some float bowl drain screws so I can correctly set the float level.

According to my what I recorded on my paper when I shimmed the valves, my valves are now sitting at:
Intake:
#1 .004" <-- adjusted from .0025" (Y285 to Y280)
#2 .005"
#3 .005"
#4 .005" <-- adjusted from .003" (Y280 to Y275)

Exhaust:
#1 .007"
#2 .0075"
#3 .0065"
#4 .009" <-- adjusted from .006" (Y??0 Y250) <-number was worn off old shim

My slides do clunk, I made sure of that, I even polished them a bit to make them real smooth.

With the pilot circuit, I will blow them out again just to make sure they are unclogged when I go to set the float height. Just curious is there ever problems with the o-ring getting caught in there?

Here's my problem with idling as it currently stands with the main needle clip set at 2nd from top (where it has ran best): The bike will idle lower around 1000-1200rpm but sputter and die eventually, but if I blip the throttle it will idle up to 3000+rpm and stay there for a while until it works it way back down to 1000-1200rpm. I feel like it is kicking into the main circuit and holding there (even with the throttle closed). I am just curious on your theories about this, maybe it's too early to tell due to other problems...


There's so much to address here, but I am taking this all in and is helping me immensely.

 

The float level adds hydrostatic pressure to the fuel that travels up the emulsion tube and pilot circuits. This pressure + the vacuum from the air velocity in the venturi draws the fuel out of the bowl and into the air stream. The higher the fuel level in the bowls, the greater the pressure and more fuel that goes into the air stream (richer). Too low, and there is less pressure, resulting in less fuel (leaner).

You don't technically "kick in the main circuit" until the jet needle pulls completely out of the emulsion tube. You're on the jet needle circuit as soon as there is enough air velocity in the venturi to lift the slide.

The velocity in the venturi affects which fuel circuit you are on. The butterfly valves (throttle position) only affect the mass flow of the air though in the intake. The slide balances the two to regulate the air velocity (fuel circuits) based on mass flow (demand, throttle).

Sputter and dying at idle shows that you don't have the idle circuit tuned yet. Likely, your sync is still way off, so you'll have one carb with the butterfly more open than the others, activating it's needle circuit and pulling the other cylinders along (whose butter flies are still closed and not even on the idle circuit). When you open the throttle, you activate the off idle circuits of the carbs whose idle circuits weren't even contributing.

So basically by opening the thottle, instead of getting a smooth transition between 4 carbs, you get one pulling the others along off idle circuit (but at an idle rpm), then abbruptly, all four carbs are in their off idle circuit, and the rpm jumps.

Also, have you checked for air leaks (propane test)? How do your intake boots look?

 

Let's back up a step.

Your valves aren't in spec yet.

If #1 intake is at .004" it's still too tight; .004" = 0.10mm (0.1016mm) spec is .11~.15mm.

If #4 exhaust is at .009" it's too loose; .009" = 0.22 (0.2286mm) spec is .16~.20mm.

While not "horribly" out, it won't make getting an accurate vacuum sync any easier.
It really helps if you use "true" metric feeler gauges.

Also, when you talk about "completely breaking down" the carbs, did you pull the butterflies and throttle shafts out of each individual carb; and replace the throttle shaft seals trapped therein?

 

Also, fintip mentioned wet test. Was the plug wet when you pulled it? That's carb float issue (right, experts?)

I had very similar issue - weak idle, sluggish, so I cleaned carbs over the weekend - found a bad float needle on #2 - did some investigating and same thing, no combusto, no hot exhaust. Spark plug is wet. Waiting for chacal's package as we speak.

 

Nicely said manbot. Information like that is gold to me. I feel like I'm banging my way around this motorcycle trying to fix it, but it's just because I don't know enough. As far as the intake boots go, they look to be crack free. The rubber has hardened of course. What does the propane test entail?

I have replaced those throttle shaft v-seals. I remember doing it the first time around when I completely rebuilt the carbs years ago.

Yes the plug in #2 is always wet.

Here's a TODO list just to get all cylinders firing and the bike idling:
1. Wet set float heights
2. Verify pilot circuit is clear
3. Check for vacuum leaks
4. Start pilot screws 3 turns out
5. Maintain jet needle at 2nd from top (?)
6. Bench-sync
If there is anything to add shout out.

I bought this motorcycle as a fixer-upper and boy I got what I wanted! 8O I almost gave up on this motorcycle, and it would have been down the road if it wasn't for this forum and all the helpful guys on it.

 

I continued the thread here because I'm ready for fine tuning the XJ.