I have not tried hooking the aux tank to the carbs with them on the bench. I will try that next. And yes, the only things connected to the intake's vacuum ports were the syncronizer hoses. The carbs also have 4 vacuum line connections, but those are capped as well. I need to go back and examine exactly where those open to.

Please keep asking questions... it makes me think!

 

The cap has a tiny vent hole, but I do also keep it only loosely sitting on the tank. Next run I'll keep it off completely to make sure it is not affecting anything. The hose that came on the aux tank is excessively long. I should really shorten it.

 

Could you send a picture of the carb vacuum lines ,are they on the rubber inlets?, not sure about these , and are the airvent pipes to the carbs clear

 

The vacuum inlets (that the syncronizers connect to) are just below the rubber boots. They are really inset under the carbs and I couldn't get the phone in there to take a pic. You're question however, made me think(!) ... there are 4 vacuum line connections on the carbs themselves (actually 7). I've attached the sticker on the air box which diagrams the connections. Anyway, it occurred to me that the connections on the intake manifold (below the rubber boots) are true vacuum lines. However, the ones on the carbs themselves are for sucking in fumes from the canister. The fact that they expect inward flow (rather than being a closed vac line) means that they could possibly affect vacuum and pressure in carb passages (and their being uncapped will most likely not affect the mixture).

I will be gone for the weekend, but as soon as I return, I will try running with those lines uncapped.

There are also 2 large diameter lines which connect to T fittings between carbs 1&2 and 3&4. They are also for inhaling fumes (I think).

In any event, I'll try various combinations of uncapping those lines and see what happens.





I'm off to sleep now. Thanks (as always) for your suggestions and insights!

 

Yes the large tubes between 1 and 2 , and 3 and 4 are carb breather tubes and are open to atmosphere, dont think the capping on the carbs in picture is a problem, have a nice weekend , will do some further looking into it

 

FIXED ?!!

I originally thought stuck float valve(s) would seem to be a likely cause of the symptoms, but those floats were in perfect condition, and the valves had absolutely no tendency to stick in the valve seats. After seeing the results shown in the previous videos, I concluded the valves were not mechanically sticking, but some how vacuum locked opened or closed (or both at different times).

Then the light bulb went on... I had removed all of the intake tract emission control hoses (with the though of eliminating potential vacuum leaks.) I capped all the (what I thought were) vacuum lines on the intake manifold and carbs. Well, it finally occurred to me that some of things I capped were vents, not vacuum lines, and needed to be clear to equalize air pressure in the carbs. I uncapped the two ports (one between carbs 1&2 and the 2nd between carbs 3&4), and the bike started instantly (on choke). I removed the choke a minute later (it kept running!), no fuel fountaining from top carb vents, and it responded to throttle (for the first time in months!)

So, following the soak in carb cleaner (a month or so ago), there was most likely nothing wrong with the carbs after that point. It was simply the capped vents keeping things from working.

In any event, I think maybe I'm out of the woods... and almost on the road. Thanks to everyone, especially CaBaRet and Hamlin6 for all the help, suggestions, and most importantly, moral support. This was quite a journey. If you're ever in Northern California, please let me know... I owe you guys a beer ...

I'll post some pics when everything is back together.

 

That is awesome news. I am very happy for you. It is a good feeling to get on top of something that has given you fits.
You showed a lot of determination and that is what is needed sometimes.
You should be proud.
I would suggest now that you have it sorted out that you take another look at syncing. You may need to tweak it some.

 

Well done , glad you stuck at it, Like Hamlin says ,few more tweaks and the open roads are yours

 

I resynced them, and there were 2 cylinders that were a little off from #3. Not bad, but I'm glad I checked, 'cause now they are dead on.

It's such a thrill to twist the throttle, and have the RPMs actually increase! Tomorrow, I will start bolting all the body panels back on and hopefully it should start looking like a proper CBR again.

 

There is a fair amount of satisfaction knowing your bike 8s tuned in properly. There is even more knowing you did it yourself..
Take pride in that.