xj550rk - 'burbling' at low rpm / throttle opening

-valves in spec
-carbs cleaned and nearly ALL brass replaced
-throttle shaft seals, pilot o-rings replaced
-vac sync
-floats wet-set


I'm experiencing a condition after my rebuild that's got me a bit confused.

During the initial rebuild of the carbs (first time) I had missed a deformed edge on #4 butterfly valve - which made an awful running / tuning experience.

New butterfly shows up in the mail, replaced..re-sync.

The bike starts perfectly with choke, and without choke when warm. Idles well.

Once moving, in any gear, throttle openings between just above zero, and below 1/4th throttle I get what I can only describe as a burble, or a blubber.

Is this most likely a rich/lean condition, or a spark issue, or something else completely?!

 

How did you set your pilot mixture screws? Any intake or exhaust modifications?

It sounds like a lean condition in the pilot circuit to me, where the bike can idle fine, but once you put any load on it, it runs rough until you get on to another fuel circuit.

Besides setting the pilot mixture screw, vacuum leaks can also cause a lean condition, and they can "open up" with higher revs.

 

Where did you set your pilot mixture screws after the carb cleaning?

 

Pilot screws are at between 2.5 or 3 turns out.
Stock airbox, UNI filter, 4-1 exhaust

I lied when I said up to 1/4 throttle, it's not that much.

If I'm cruising, it feels burbly. If I'm on a little more (such as a hill) to maintain speed, it clears up.

It's hard to tell if the bike idles on all 4, doesn't feel rough or anything - but assumptions are always able to be incorrect

 

So you're talking "trailing throttle" essentially.

You may need to do some additional carb tuning for the UNI filter and 4-1 exhaust.

 

I'll fiddle with the pilots a little, my colortune has been on backorder for a while now.

I'm wondering if the aftermarket jets from chacal are slightly different than the pricier mikuni replacements?

I originally had this issue, to a lesser extent where I had a bad sync- one of the carbs at rest had a small gap in the linkage between the spring opposite the sync screw. That's not the case this time around, a 'learn from your mistakes' proverb has learn'd me.

 

I've always had this same burble when off load. I've just lived with it, BUT my pilots are rather rich. I may back off a bit in the spring and see if it helps some.