Gas pouring out at start-up

[fullercameron]

Looking to see if anyone has any good advice. I have taken these carbs off so many times now I feel like I'm ready for the friggin' pit crew.

I was having issues with plugs fouling and stumbling and eventually dying at idle. I got to the point that I figured it was the float valves in the carbs. I took the carbs apart and cleaned them and replaced the float valves and checked everything else over. The bike was running much better. No more plug problems and everything seemed in oder until I parked it the other night and when I came back it had puked about a pint of gas all over the floor.

Took everything apart and checked float height and needles again. Seemed fine so I rode it to work - gas everywhere. Took it to the shop and found that if I burned up most of the gas in the bowls by shutting off the fuel a couple of blocks before I got home, there was less of a problem. This leads me to believe that I got shitty float needles when I got the new ones - does this sound like that is the case to anyone else?

Today I took the carbs apart and checked everything again, this time I tried a bit of yellow teflon tape on the threads of the float needles because I saw it suggested somewhere on the forum, but when I open the petcock, the gas seems to be flowing out of the carburetor as though the float valve didn't even exist. Today with the air cleaner off, I can see that it is coming out of the clear tube on the inboard side of the carb as well as backing up out of the main air jet hole in the front of the carb. Is it really possible that the new float needles are this terrible?

The new parts came from a keyster carb kit from mike's. It was only 5 bucks more for the rebuild kit as opposed to just ordering float valves, so I got the lot. I'm ordering new valves tomorrow. Does anyone know where I can get real mikuni float valves? I am going to call MMM at 650 central on Monday.

I am about a week away from freaking out. Rode the bike almost 500 miles last week and I'd really like to keep going but I'd rather not be the traveling fireball.

 

[azman857]

How are the float themselves? Brass floats can split and leak and don't float anymore. Couple ways to test it to shake the float and listen for fluid sloshing. Hold the "cold"(ambiant temp it fine, not fridge or freezer cold)float in warm(the warmer the better, but not steaming or boiling) water and wait for bubbles to appear in numbers, and not the odd "hanger on".
If they are foam type just place them in water and see if they float. They can become satuated and not work anymore.

 

[fullercameron]

Azman

The floats seem to be fine. Every time I take them out, I shake them to see if there is any gas inside of them and they seem to be empty. They are the original brass floats from the '72 bs38's on the bike.

I'll try submerging them on their own to see what I get.

 

[XSBastard]

Azman

The floats seem to be fine. Every time I take them out, I shake them to see if there is any gas inside of them and they seem to be empty. They are the original brass floats from the '72 bs38's on the bike.

I'll try submerging them on their own to see what I get.

Hey fullercameron

I just had the same problem. The floaters seamed fine and I adjusted the floater height caveman style...nothing worked...even the floater needle wasn't stuck....THEN it hit me, there is a moving part inside the floater needle. Take your floater needles out and make sure that the "knob" on the top of the needle can be pushed in and then should retract. If not you have found your problem. The part is $5 at mikesxs
I hope this is your fix as well

 

[XSLeo]

Just a thought, the pins that push into the needle go against the arm on the float, not up toward the seat. If they are in upside down they won't work. Also when you set the float height you want the float arm just touching the pin, don't compress the pin.
Leo

 

[fullercameron]

The float needles are new and they are definitely in the proper direction. Both of the pins appear to still move up and down properly when they are compressed.

I set the float heights with the float tang resting on the pin of the float needle but it was not compressing the spring inside of the needle.

One of the needles looks fine when I visibly inspect it and the other float needle seems to have what looks like a ring around the tip at the point that it would seat. Should there be any visible marks on the tip of the point where it seats? It seems to me that this could be the problem but I am not sure if the tips need to be completely flawless to seat properly. Again, the bike runs great once it is up and started, and it almost always starts on the first kick, but if I sit at a light too long or open the fuel supply before I am moving, I end up with a pint of gas on the ground.

I guess I am also just curious if anyone has ever gotten a complete crap float needle that wouldn't seal right out of the box?

 

[XSLeo]

The point on the needle should look good, an obvious flaw will keep it from sealing.
Sometimes the needle seat can have a burr on it. Take a Q-tip. Pull off most of the cotton, wrap some 0000 steel woolaround the q-tip. Use this steel q-tip to polish the needle seats. not real hard just to polish off any possible burrs.
Test on the bench for function. Hook up a small fuel bottle to the carb, with the float bowl off hold the float up with a finger. Turn on the fuel. Let the float drop and lift it a few times and watch the fuel flow does it turn off and on as the float moves upo and down?
What year carbs are they. The BS34's have an o-ring around the float valve seat. If this o-ring is bad it lets fuel leak past the outside of the seat.
Have you read www.amckayltd.com/carbguide.pdf yet. If not you might want too.
Leo

 

[fullercameron]

Leo

thanks for the tip on polishing out the burrs of the seat with steel wool. I have some 0000 stuff at the shop and will try that tomorrow. I hadn't thought to set up a way to bench test the float needles, so this is also a big help. I think that it will at least save me putting the carbs on and taking them off again if it doesn't work.

I've read through the carb guide and I can't see any reason other than a burr or defective needle that could be causing this. The floats have never appeared to have any liquid in them when I take them out, and I have checked and rechecked the float height so the only thing I can figure is that there is a problem with the needle and seat.

I'll try the fix tomorrow and report back.

-the carbs are '72 bs38's which have float seats threaded into the body of the carb, so there's no o ring on mine that can cause a problem. I also tried fuel resistant teflon tape on the threads so I don't believe that the problem is fuel getting past the threads.

 

[XSLeo]

I have a plastic tank of an old lawn mower. I put a short piece of hose, a shut off and a long piece of hose, a tee fitting with more hose to hook to the carbs with. I use this to bench test carbs and to test run bikes with out the tank on. It holds about 1 3/4 gallons of gas, don't often need that much but thats what I got. Lots of old lawn mowers around should be able to find a tank cheap to free.
On the seats threading in then they should seal ok. Good gaskets there won't hurt.
Mike's has had some quality issues in the past. If the steel wool won't help you might try getting genuine Mikuni parts. Most any bike shop should be able to order them. Just take along what you have.
Just a thought, do you still have the original float valves? The steel wool can help clean up the old seats. Maybe look the old needles over, they might be better than the new ones.
Leo

 

[CalsXS2]

Dang it Leo. You beat me to it. I was going to suggest putting the old needle's back in and see what happens.

Did you have this problem before you changed the needle's?

 

[gggGary]

To check floats submerge them in a cup of HOT water for a few seconds. If they are bad air will bubble out.
Very fine rust from a not spotless gas tank can quickly destroy even new float needles.

 

[fullercameron]

Spoke too soon. Took the carbs apart again and bench tested the float needles to see if they closed properly if I lifted the float. The needles passed.

After comparing the float weight side by side, I did notice that one was considerably heavier than the other. Vigorous shaking did in fact reveal that I had a float full of gas. Ordered new floats so I should be back in business when they get here Friday.

Thanks for the help.

 

[gggGary]

If they are from the popular XS supplier check them carefully for interference with the bowl and freedom of motion, just thought I'd mention it.

 

[I am Carbon]

Spoke too soon. Took the carbs apart again and bench tested the float needles to see if they closed properly if I lifted the float. The needles passed.

After comparing the float weight side by side, I did notice that one was considerably heavier than the other. Vigorous shaking did in fact reveal that I had a float full of gas. Ordered new floats so I should be back in business when they get here Friday.

Thanks for the help.

don't you just hate that. good to see you found your problem. my quickie test is with carbs empty turn them upside down and blow into fuel line and if i hear air the seats are leaking no air seats are fine it works for me

 

[fullercameron]

Thanks for the advice gggGary. Is there a specific part of the float you have had interference issues with. I'll check them over for movement, but if there is a specific area that has problems I'd love to know where to pay particular attention.

 

[fullercameron]

Just a question to satisfy my curiosity, does anyone have a good explanation as to why this problem would have progressively gotten worse over the first couple of weeks of riding the bike regularly?

The only thing I can figure is that when the engine got warm, it warmed the carb enough to pressurize the float slightly and when the engine cooled, the float cooling created suction that drew gas into the float a little at a time.

It ran really great the first few days after I put the new float needles in following my previous carb problems. It was about day three of riding that it started to leak a little gas when you weren't looking - and by day 7 or 8, it was leaking everywhere as soon as the fuel supply was turned off.

 

[gggGary]

Look closely at your floats. It is fairly common for there to be a series of cracks around the perimeter of the float. So I think you have it; heat cool cycles tend to fill the float with gas. Try my little hot cup of water experiment with your leaky float and the other one too.

 

[fullercameron]

Didn't get my floats today. Was hoping they'd get here early so I could ride to work tomorrow. It'll have to wait until tomorrow.

Got bored so I decided to paint my helmet. not perfect but I think it looks pretty sweet.

gggGary, I looked at the float that was leaking and sure enough, there were many, tiny, nearly invisible cracks along the perimeter of the float. Can you actually get all of the gas out of these things and repair them by soldering or is it more of a hassle than it is worth. Seems like you'd have to be careful about adding too much weight with the solder as well as the flammability of gas issue.

 

[gggGary]

I don't think they are repairable. (I have tried).
A they get heavy real quick
B You fix one spot another spot leaks
C It gets too hot and Collapses when it cools, IF you do seal it.
D The float is critical and the repairs are dodgy at best.

Love the helmet paint!

 

[fullercameron]

I kinda figured that between the gas, and the weight they were pretty much junk. Just thought if they were fixable it would be nice to have a spare. I'm sure I'll find something else to spend my time.

Glad you liked the helmet paint. I've been toying around with some striping and painting recently. Did my truck a few months ago. I figure with the helmet, I'll look like I'm going fast until the carbs are working again.