Running rich, rich, rich!

Rich to the point of dripping spark plugs, billowing black smoke out the exhaust.

Clink the link in my signature line to see my mods, but basically I have an 82 XJ750 Bobber. Stock valve clearances, good leak down, good compression. MAC 4 into 1 exhaust and individual pods (I know), and the bike is running super rich with stock jetting and idle screws at 1.5 turns even.

We swapped the carbs for a known good set off of another bike, same results, super rich. We think it's something other than carbs, but are at a loss. Seem to have good spark, but for some reason are unable to burn the fuel.

Thoughts???

 

Are your plugs dripping with oil, or gas? Going with pods and an aftermarket exhaust w/ stock jetting should make you lean as hell, not rich.
When you say the carbs are "known good carbs", did they come off of a bike with the same engine and mods as yours?
Float levels correct?
Not sure how the YICS system would affect this.

 

The bike the other rack came off of does not have the exact same mods (and smaller jets), it has open exhaust and drilled out airbox, but we thought it would at least change if not correct the issue, not continue to run so rich. The plugs are soaked with gas when we pull them out.

Would the float levels cause this sort of richness?

 

If the fuel level is way too high in all of the four bowls, that's what you will get, yes, ultra rich mixture.

 

Float levels would be a universal setting, yes? Meaning, if his carbs run fine on his bike, the float levels should be suitable for my bike?

He is running a smaller jet setting in his bike than I am, yet his rack runs just as rich on my bike as mine does, yet fine on his. We're thinking the problem is on the bike rather than the carbs.

But we're stumped...

 

Check your crankcase for gas

 

"Stock valve clearances." Does that mean they've been checked and adjusted to within spec; or they're "stock" as in, ignored?

If the float levels have indeed been accurately and individually wet-set, then there are a few other possibilities. But I would think the problem would reveal itself in a good wet-set session.

Another admittedly remote possibility is that both sets of carbs have enrichment-valve ("choke") issues of some sort.

"Seem to have good spark." What plugs are you running?

 

One of two things: you don't have good fire on the plugs or you don't have good compression.

If compression tested good recently (what were your readings?) then start checking your fire. It could be plugs, plug wires, coils, TCI...

 

We got it to run good with another set of carbs so we're back to diagnosing my carbs. I adjusted the valves to within stock specifications.

 

Wow, ended up that the PO swapped the air jets, hence it never ran right to begin with. Tuning has now resumed....

 

They are shown the wrong way in most manuals, so this is a very common mistake.

 

Verified by photos on this forum, thanks guys!

 

Got it synced and the idle tuned in, worked the needle a bit with much success before the rain and temp drop hit. Should be warm the next several days so we can get some runs and shut down passes in. Should be riding for fun by Wednesday!

 

Oh, and an oil change...