Help! Black sooty on #2 only

[Guest]

So I've been searching and searching and found some relevant information, but none of it has helped me.

#2 plug is black and sooty. Stays black sooty when I swap #2 and # 3 plug leads. This tells me carbs could be the issue.

I have done the following:
Swapped leads.
Grounded the plug on the frame - # 2 is showing strong spark.
Felt the exhaust pipes - #2 heats up just like all the rest, from cold.
Cleaned the carbs about 4 times now. By clean I mean I've squirted carb cleaner through all the ports and jets, removed the pilot and main jet and visually verified they're open, removed the needles and slides and verified no gook built up on the ends, assured fuel flow into all bowls, set floats heights and assured all floats actually float. 1st time I also replaced the o-rings and the o-rings behind the intake boots.
Replaced the vacuum line to the fuel valve.
Replaced spark plugs.
Compression test yielded between 130 and 145 in all 4 pots.
I am at a loss as to what to do next.
Any suggestions?

Oh yeah, 84 Katana 750 (same as a GS 700E, basically)

[tkent02]

I bet the petcock has a bad diaphragm letting fuel get sucked down the vacuum line into the #2 carb, making #2 too rich.

[Smokinapankake]

With the tank off, and the fuel valve set on Reserve or On, no gas drips out, so I assume the valve is okay....

How would I test the diaphragm? Sucking on a piece of hose attached to the vacuum fitting on the valve?

[tkent02]

With the tank off, and the fuel valve set on Reserve or On, no gas drips out, so I assume the valve is okay....

How would I test the diaphragm? Sucking on a piece of hose attached to the vacuum fitting on the valve?

Suck a vacuum on the vacuum line, does fuel come out?
Mouth suction probably isn't enough. Use a pump or hook it to the engine when running, check for fuel in the hose. Might try using a clear hose?

Or, disconnect the vacuum line from the tank and block it, run the engine with the petcock on PRI, go for a ride and see if the problem is fixed.

[Smokinapankake]

How about a big ol' horse syringe? That should be enough suction eh? Plus it catches the gas as it comes out, rather than in my mouth...

[earlfor]

Faulty petcock. Its leaking and gas is being drawn through the vacuum line.

Earl

[Shaughn]

Yikes!

How about a big ol' horse syringe? That should be enough suction eh? Plus it catches the gas as it comes out, rather than in my mouth...

You own a horse syringe, but are unhappy about a little gas in your mouth?

That sir, is an odd juxtaposition

[Smokinapankake]

Funny. I use it to aid in the brake bleeding process.

[Smokinapankake]

So I took Tkent's advice and plugged off the vacuum line, set the valve on prime, and went for a ride. Maybe 5 miles, 7 at the most. Plug looks a little better, but still sooty. Not enough miles to burn it off?

[tkent02]

Ride, Sally, ride.

[earlfor]

So I took Tkent's advice and plugged off the vacuum line, set the valve on prime, and went for a ride. Maybe 5 miles, 7 at the most. Plug looks a little better, but still sooty. Not enough miles to burn it off?

Nah, probably take 25 to 50 miles.

Earl

[Smokinapankake]

My commute to work and back is 36 miles - I'll check tomorrow and update.

Thanks for the help!!

[Smokinapankake]

Now I'm really confused....

So I rode to work and back for a total of 36 miles, ranging in speeds from 25 to 60, up to about 6000 rpm at the highest. The majority of my ride is between 50 and 60.

Got home this afternoon, pulled plug #2, and.....

still black and sooty. About like it looked Saturday night after 5-7 miles.

This was after I bypassed the fuel valve, plugged off the vacuum tube and set on prime.

What gives?

Here's the setup:
84 Katana 750
Stock exhaust
Pod filters, bigger (unmarked, out of my 82 Katana which is in pieces right now) mains, and the clip has been moved to the 2nd notch down from the top, keeping the nylon spacer on top of the clip. Air screws set at 3 turns out.

Plugs 1,3, and 4 all look kind of rusty brown. Still a bit rich, but I'm done messing with settings. I have a replacement airbox coming from a salvage yard in CT, and once it comes in I'm running with my tail tucked between my legs back to the stock setup (117.5 mains, clip set at 3rd notch down, air screws at 1.5 turns out - that's how it came to me anyway and it seemed to run okay then).

Still, none of this would explain why the #2 jug is so rich.

HELP Please!!

[Smokinapankake]

Bump - anyone?

[Zook]

Maybe the #2 float valve is stuck or not seating correctly or a piece of crud got into it causing the carb to flood a bit.