Fuel delivery issue?

I have been working on an 82 xj650 which I bought not running. My friend rebuilt the carbs for me. We set the float levels very carefully by eye/manually. In other words we gave it fuel supply from a little bottle holding the bowl in place without screws in it and then pulled the bowl straight off to see how full it was. We set the float in each carb so the fuel filled the bowl a little more than half, figuring we should at least be able to get it to run that way. The new needle valves that came in the rebuild kits seem to stick in the closed position but after a lot of playing around we got each one so that the float and needle valve seem to interact correctly.After putting the carbs back on, we set the petcock to PRI and got it to run but it was running so rich it blew white smoke everywhere (i mean a lot!) But it ran on its own, without starting fluid after firing up. Not for long, but on it's own.
After I let it sit for a while I tried again. I put the petcock in the run position with the airbox disconnected and while cranking sprayed a shot of starting fluid across the span of the carbs. It fires up, races for five or six seconds and dies. No clouds of white smoke either. I don't want to continue doing that as running on ether isn't great for longevity, but I keep arriving at the same suspicion. Is it possible that the petcock is faulty? I rebuilt it but it doesn't seem like it's working in the run position. Just runs on the ether until it's eaten that up and then back to sleep.
Is there a good way to test it bypassing the petcock without feeding it too much fuel - like there is in the prime position? If it doesn't depend on gravity like a Model T Ford, I should be able to run a fuel hose to a container of gas on the ground alongside it - no? Would the vacuum from the engine suck up just the right amount of fuel that way? I feel like I'm groping and flailing around in the dark here, so any help would be greatly appreciated.
Thanks as always,
Scott

 

PRI bypasses the vacuum.

If your bowls are only half full, you don't have near enough fuel in them. Search through the forums and find the threads on setting the float levels, especially the detailed write-ups on "wet-setting the floats". Basically, your fuel level should be about 1.5mm below the bottom of the top lip of the bowl. That is an APPROXIMATE, not a correct measurement. READ the write-ups for correct info. But basically, you don't have enough fuel in there yet.

You also MUST make sure that a bench-sync was performed on the carbs. That is needed to get the carbs set where it will at least run enough to warm up to allow you do a running sync.

So you have several things that have to be in order before you'll even get it running:

1.. mixture screws cleaned and set at 2.5 turns out from soft seat.
2. carbs thoroughly cleaned as in "church of clean"
3. carbs preferably rebuilt with all new throttle shaft seals and fuel rail o-rings, ans well as mixture screw o-rings
4. carb rack bench-synced
5. floats dry-set
6. floats wet-set
7. carbs installed with boots and airbox in place
8. hook up an auxiliary tank so the bike can run for 5-10 minutes with a fan blowing at the engine since it IS air-cooled
9. now time for a running sync to dial it in
10. color-tune is optional, but it will help dial in the idle mix for optimum efficiency

dave f

 

Not sure I quite understand your theory on the carbs sucking up fuel from a can on the ground :? The carbs are gravity fed from the petcock, the only thing the vacuum line does is switch it on & off.

The way the petcock works on these bikes is fuel should flow all the time in the PRI position, and in ON and RES the fuel only flows when there's a vacuum applied to it's smaller hose. Try applying a vacuum to the petcock manually & see if fuel starts flowing out of it. If it does, and stops when you remove the vacuum then it's working.

You may have found one of the problems with cheap carb rebuild kits in the rubber tipped needles which don't like ethanol & can stick closed. You'd be better off getting metal tipped needles from chacal...

Also you need to properly wet set the floats rather than guesswork to be honest (you use a piece of clear tube on the drain spigot, run up the side of the carb to read the level. Reading the contents of the float bowl tells you nothing as the volume of the float has been removed & the level will be way down anyway. But I suspect your primary issue is the rubber tipped needles sticking if they were doing it before.

 

http://www.xj4ever.com/setting%20fuel%20levels.pdf

 

For all three super-helpful responses, THANKS VERY MUCH. Won't work on it again till next weekend, but I'll order whatever I need tomorrow and print out all the instructions for each step. This bike is going to be running on the weekend.
Again, thanks.
Scott

 

No mention of valve clearances. It's not going to run right, nor will you be able to sync the carbs, if you've got a bunch of tight valves.

Step one in "carb" tuning is to get the valves in spec.

Once that's done, you might want to consider a compression test to ensure that it has a hope of running.