Basket case carbs

Hello everyone. I have been lurking these forums for about two weeks attempting to trace various problems. Through here I have found the service manual and have read numerous threads on how to clean/sync and diagnose carb problems.

What I am dealing with: My friend bought a $400 1985 xj700x water cooled with the mikuni carbs, BS33's from what I have learned on here. The previous owner took the exhaust off in an attempt to make the bike more "rumbly" and then decided to delete the air box and mess with the carbs. Herein lies the problem.. I received the carbs completely disassembled. He must have gave up because he clearly did not know what he was doing. They were still on the rack but the bracket that holds the idle screw was put on backwards, which leads me to believe it is possible he completely separated the carbs from the rack previously. I ended up assembling everything, cleaned out all the fuel and air passages, set the floats, put new o-rings on the needle valve seats ,jets, made sure the needle valves themselves were absolutely free of any defects and that they create a good seal, etc.

The good news is I got the bike to fire and rev BUT as soon as fuel goes down the main fuel line between carbs 2 and 3, gas starts pouring out of the overflow tubes between carbs 1 and 2 and carbs 3 and 4. I know this is usually a needle valve seat issue but I turned the carbs upside down and blew air through the fuel lines to be sure that no leaks were present. Even used soapy water. Only thing I noticed was a tiny bit of air was leaking of one of the overflow tees. That shouldn't be a problem since really if everything was set properly, the overflow tees would never see fuel.

I double checked everything. There aren't any blockages, floats and needle valves all check out and all the jets are flowing free. The pivot pins on the floats allow the floats to move without binding. The floats themselves were tested in gas and they're free of defects.

What I have noticed is that when air is blown through the main fuel line, air escapes out of both overflow tubes...Is this normal? I figured the fuel input would be a separate circuit so to speak from the overflow. I could be mistaken. Is it possible that carbs 2 and 3 were mixed up by the previous owner when he was reassembling them and that is the source of the overflow problem?

I need some help from someone who knows these carbs inside and out, otherwise I'm going to have to go in this blind. Thank you in advance

 

no mention of throtle shaft seals being replaced.
you have to wet set the fuel levels in carb bowls
Setting the fuel levels
fuel overflows from the carb bowls and goes up to overflow vents when needle valves do not close
air blown through input fuel line will go out the overflow tubes because the needle valves are not sealed unless full of gas to seal hole allows fuel flows into bowl
look at this for views of carb cut away

Something New, Something Naked

then read this
IN THE CHURCH OF CLEAN

when first filling carbs sometimes you have to rap them with a screw driver handle to get the needle valves to do the job as they may bind up when first filling

 

take bowl off the carb turn it upside down and with a flashlight you will see where the excess fuel goes if you shoot some spray down the overflow you will see it . put on googles for this

 

Thank you for taking the time to respond. I have already read the church of clean thread numerous times and have followed it. I have also "wet set" the floats and had a vernier caliper handy to compare with the service manual I have.

I have yet to try rapping the carburetors so I will give that a shot. You are correct that I have not replaced the throttle shaft seals. Nothing is leaking from there, would that affect the overflow situation? If so I will get on that asap.

As far as the needle valve not seating...That would make sense but I have flipped the carbs upside down with the bowls off, plugged both overflows with my fingers and blew through the main line to detect any sort of leakage. There was none. To confirm this I had someone modulate the float manually allowing air (would be fuel) to go through the needle seat. Even sprayed soapy water on the needle valve itself to see if there would be any leak. Also you are saying that air would escape the overflow if the valves are not seated...What if let's say theoretically they were seated and the overflow tubes were still overflowing? That would be the issue then?

But I will be posting pictures/maybe even a video showing the full diagnostic procedure in case you or anyone else can see what I am missing. I will also do as you suggested and spray down the overflow (with goggles on) and see where it's going.

I also thought maybe of using a large plastic container to dip the carburetor right side up in gas with the bowls off to see if indeed the needle valve or floats are to blame. If I blow air through the main line I should see air coming from the needle seat if it isn't sealing properly.

Thank you again, really appreciate it.

 

Welcome aboard.

Sounds like a challenge you have on your hands and you said you already wet set the carb float levels on a bench.
You didn't have any leaks then did you?

The throttle shafts seals could leak vacuum, but wouldn't be related to your problem with the fuel overflowing.
I have some pictures of the BS33's if that will help?

Tony

 

So far these are definitely one of the most challenging carbs I have ever encountered. I don't think it would be this bad had the carbs not been tampered with by the previous owner. And to answer your question, yes I wet set them according to the church of clean thread with the carbs vertical. I did it the same way I've done carbs my entire life using aquarium tubing hooked up to the bowls and having the fuel level just a couple mm beneath the mating surface. This is why I will have to try rapping the carbs as maybe the needles somehow aren't doing their job.

 

the pressure the fuel puts on the needles is so small, you'd probably just blow them open before you knew it.
if you use your same idea but put red dyed kerosene in a long fuel line you might see the gas turn red near the bad carb.
could the connections between the carbs be leaking

 

Now that's confusing - you've wet set the carbs successfully, yet they are now leaking fuel out of the breather/overflows?
It's not unusual for a rebuilt set to leak initially - mine did, but a quick shake solved it. If fuel is coming out of the overflows it will be coming out of the jet, needle, carb throat? When you dry set them the reading should be taken with the tang of the float just touching the needle valve, by tilting, not turning them upside down - is this what you did?
There is no connection between the fuel inlet and overflow outlets, other than the fuel level.
I would suggest re- doing the dry set, then rig up a fuel rig to wet set them again.

 

For the initial dry set the carbs were tilted not upside down. I made sure the shock absorbing pin was not depressed as you said. I will redo everything again on Wednesday. I just started a new job which is taking away from cool stuff like motorcycles . I will give everyone an update then. Thanks again.

 

are you using the same fuel reservoir for wet setting and for checking on bike , I ask because if you are using the bike fuel tank when the carbs are on the bike, if full, would put a lot more pressure on the needle valve than a small auxillary tank.
stu

 

If the carbs did not leak when you did the wet set off the bike, they should not leak on the bike unless a needle is binding or something similar. I learned the hard way to let the carbs sit for a while when wet setting and also to shake them a little bit just to make sure they didn’t leak and that the levels stayed constant.