I know this sounds a strange request but could you try the sync first , it could prove interesting

 

Will do. It's now a little after 10am, and I've spend the last 1.5 hours after waking up contemplating and writing the previous post. I shall go have my instant oatmeal and bagel first, and then hook up the synchronizer.

 

I've synced the carbs which were amazingly close considering I've fiddled with the sync screws during assembly. I've also kept my phone in one hand and video'd the process and symptoms.

Warning... this is raw, unedited video, with moments of pointing at nothing (whilst I adjust or fiddle with something), and shaky/rapid camera movements.

Below, I'll relate some insights rewatching the videos has provided. Also, you may notice a "4" on the #1 carb. These numbers are for keeping carb parts together with the same carb, and not a carb/cylinder number (although I should have initially made them one and the same). I point this just to show I am not entirely dense.

The first video begins after I had started, and let warm for a few minutes. The bike is running on choke. At this point, it will not run off choke (as demonstrated). The first dozen seconds is me trying to find the sync screw without looking.


The second video picks up after I needed to set the phone down to manipulate the choke, throttle, and idle adjust after the bike was warm.


Insights:
- No fuel seeps from the jet needle orifice (which is directly connected to the main jet), even when I manually lift the slide with engine running. This means the fuel level in the float bowl is not filling up to the main jet. This is extremely telling and something I should have thought of earlier. Even with little vacuum in the throat barrel, I would expect fuel to come from the main jet especially when the needle is lifted.
- After watching the video, I saw something I've never noticed before. Fuel is seeping from the gap where the air horn sits on the plastic surround. If you watch carefully, you can see fuel come from this gap. This means fuel is coming from the vents that sit just under the air horn. (These are the vents I'm referring to

Should fuel ever come from these?

Also, there's a few seconds in the video where I show light white smoke coming from the exhaust. This is on a very warm day after the bike is warmed up (so it's not initial start up condensation.) I believe (hope) it's due to gas that has seeped into the crankcase, and it's the gas in the oil burning off.

Quite a puzzle, but it keeps leading me back to thinking it's a float/float valve issue. Next test is fuel level in the float chamber. I really appears as though the chamber is not filling completely with fuel (not up to the level of the jets) as no fuel comes out of the main jet even when the slide / jet needle is lifted.

Saga continues...

 

Right it will be telling to see the float heights through the clear tube

 

New insight!

I removed the air horn, and when I start (engine is still warm so requires no choke),

Fuel fountains from the 'vents' on top of the carb. THAT is where the engine is getting it's fuel to run off choke. I believe it's overflow. The fuel in the clear fuel line I connected to the drain is at or above the height of the float bowl.


This almost certainly points to float valve sticking closed... then open.

The question is HOW. The floats are in good shape, and exert significant buoyancy force when submerged in water. The float valves exhibit no sticking of any kind and seem to move freely when lifting on the floats.

However it just occurred to me that gasoline / petrol is less dense than water and will exert less force on the floats.

 

I think the clincher will be to re-run the fuel / float chamber height test when the engine is cold and exhibiting its 'run only on throttle'. If the float level is very low, that will positively ID a sticking float valve.

It just amazes me, however (and makes me a bit skeptical at my conclusion), that it happens across all 4 carbs.. AND they all seem to begin 'overflowing' about the same time.

Next test, I will have 4 fuel level lines on all 4 carbs, and remove all air horns to monitor overflow.

 

Just thinking out loud... I had written in an earlier post a question asking where the fuel enrichment (cold start) gets its fuel. I had already been told the answer (just forgot)... it's the third 'jet' protruding into the float chamber. My other question 'was it possible for fuel enrichment (FE) to get fuel before main jet.' I'll need to measure the height of the main jet vs fuel enrichment jet. From memory, I think FE jet is a bit taller, and if so, then that is possible.

If fuel is metered in at just the right flow rate, and FE jet is a bit taller (meaning fuel reaches it before the main jet), then it's possible for FE to continually receive fuel but not the main jet. But this kind of blows the float valve stuck closed theory, since the FE circuit gets fuel from the float chamber. If it was stuck closed, it would starve the FE circuit as well (unless just a trickle of fuel gets in.) I could believe that if one carb was affected, but I can't believe all four carbs are similarly afflicted in such a precise way.

 

Since you live in San Fransisco, do you have a cali bike? I have no idea what difference that would make, just throwing it out there a variable. Maybe some of the other west coast folks could speak into that.

 

Yes, for sure CA bike. I removed most of the intake side stuff (to take it out of the equation and out of the way while I tried to figure out what's wrong). It basically consisted of a charcoal canister connected to:
- Gas tank vent - captures tank fumes and stores in canister
- valves connecting canister to intake vacuum lines (removes tank vapor from canister and directs into intake tract for burning.)
Lots of vacuum lines and hoses

There is an exhaust component which injects air into exhaust to promote more complete burning (or something like that). I left the exhaust components intact since it seemed unlikely to affect my issues. It consisted only of a single vacuum line to intake #3. All other vacuum inlets are capped off. I did replace the vacuum line with a high-qual silicone one.

 

Thank you for the thought! I feel like I'm close. I just need a few more of the puzzle pieces to fall into place. Every little suggestion helps.

So far my theory is, float valve can't be stuck closed.. or even the fuel enrichment (choke) wouldn't get fuel, and bike would not run.
However, if it was free, there should be fuel coming from main and pilot jet, which it doesn't look like there is (when cold). So partially open.. just enough for FE to get fuel but not the other jets? I suppose there could still be blockage, but air blasts through all jets freely.
When warm, stuck open? Probably. Fuel comes out of a top vent. I still need to ID which passage is connected to the vent the fuel comes out, and if it happens on all carbs or just #1.

Going to go buy some 3/16" clear tubing (1/4" is a bit too loose) and connect to the carb drains and do the float chamber fuel level test.