rebuilt carbs overflowing - @ random?

[DougXS2]

rebuilt my stock '72 38's - and reinstalled them and they ran great.

then I let it sit for about a week, got ready to crank it again and noticed they were leaking/overflowing like crazy. So I poked around a bit and noticed that I hadn't reinstalled the small plastic pipe that connects the two carbs (there's a large and small connector tube). gas was pouring out of that small pipes nipple - then once I added the small tube...it filled up the other carb.

I pulled them off again and pulled the bowls and noticed that one of the floats had a leak and had a little gas in it. so I ordered and installed new floats in each carb.

reinstalled them. cranked it and it ran great. road around for about 20 miles worth. Accidentally had been running on RES and managed to run out of gas (not far from a station). put another gallon in and road about a mile and half and when I stopped, I noticed the same right carb was overflowing exactly the same!!!. flowing so much that it was soaking into the airfilters.

Road home as quick as I could (about a mile or so) and when I got home it wasn't leaking anymore? (I can slosh the tank around an hear 'some' gas in there so I dont think its empty again....just isn't overflowing anymore (yet).

so my guess is leaky new float (unlikely - but possible), randomly stuck float, needle not seating randomly?

still need to pull the carbs again but not sure what to look for once I do (other than a leaking float).

what do you guys think? and what should I look for?


btw, tank is recently lined, carbs just rebuilt, new petcocks, etc,etc so I'm doubtful that its trash. only have about 40 miles on everything since replacing/rebuilding all on those things.

 

[littlebill31]

More than likely it's part of the float system. Stuck float valve needle maybe. Check to make sure everything is free and moving easily. Make sure your float pin (the one that holds the float onto the posts) is not bent. That can bind a float. And double check the float height. Should be 25mm for a '72.

 

[vr3506]

Youre petrol tank was almost empty, maybe you had some dirt from riding on reserve coming in between needle and seat.
When it's happening again, maybe close your petcocks and ride till your floatchamber is empty, than open again, this sometimes helps to remove dirt from between needle and seat

Jan

 

[DougXS2]

Those are the only things I could think of as well....

regarding the floats sticking; they're quite free and I used the new pins that came with the new floats from Mikes. I just cant imagine what or how they'd bind. but I agree it does act just like a stuck or sunken float....

and you're right Jan, trash always has to be a possible culprit.

what seems wierd to me is that it has been the right carb both times. and in exactly the same manner. making me think that what I've been working on wasn't the problem....?

the only other thing I forgot to mention was that I replaced the slider diaphrams on both carbs while I had them off too.... Im unsure how they could contribute to flooding....?

do they have anything to do with fuel level or mostly just airflow? and btw, they seemed to go on and work correctly.

 

[littlebill31]

Only the float system regulates the amount of fuel that goes into the float bowl. If it is flooding, then the float is letting too much fuel in. That would be a problem with the height or something preventing it from closing completely.

 

[vr3506]

Hi Doug,

The diaphragms have nothing to do with your problem

Jan

 

[DougXS2]

littlebill, I agree. and was afraid of that...but at least its somewhat narrowed down... I'll pull them and recheck the seat fit and the float height.

would it hurt to test that on the bench with alcohol maybe? but its hard to figure when it does it sometimes and works flawlessly the rest.

Jan, thanks. one more thing off the list of potential causes.

 

[cra-z1]

Do you have filters. I assume you replaced the needle/seat assembly,if not replace those. I made a small gauge to check the float height first then I checked the level with gas and a clear tube. If you got the needle and seats mixed up during the rebuild it could be a problem. The floats could be set correct but if the needle does not seal on the seat they will overflow

 

[DogBunny]

I think you said you used a re-build kit. The float valves in most BS38 kits are crappy. Take a look at the needle and the seat under a magnifying glass, and you will see that they are poorly made and make a poor seal. You can and should buy genuine Mikuni float valves. This may not be your entire problem, but is probably at least contributing to it.

 

[DougXS2]

ok....I think I found the problem. it was a combo of floats out of adjustment and the float needle jamming open when the fuel level got low enough.

only on the right side carb. the floats would go low enough to let the needle come down so far that it would get cocked as it was going back up and jam there.

thanks for all the help. now on to oil leaks!

 

[littlebill31]

Good. Make sure you "hang" the float needle correctly. The little wire that is attached to the float needle can go either way on the float. Sometimes it will jam, so you might have to try and reverse it.

 

[DougXS2]

hmmmm....maybe thats it then. my float needles didnt have any spring/wire retainers (I've seen what you're talking about on other carbs)......

the old or new parts didnt have those on mine?

 

[5twins]

The BS38s didn't have that retaining wire on the float needles.

 

[littlebill31]

Crap, I did it again. Why do I keep thinking 34's? Sorry, my mistake.

 

[DougXS2]

ok time to revisit this issue.

I thought I had it licked...but took a long ride on saturday and parked, got some lunch, looked out and had a puddle of gas (coming from the right carb - I think).

so my new question is....is this normal if I forget to cut off the petcocks?

I ask this because, I pulled the right carb, drained it and hooked up a big syringe full of alcohol and refilled the carb and tested when it got full. it seemed to shut off normally. I tested it further by blowing into the fuel line and the valve was shut. then when I tilted the carb, the valve opened and let more fuel (blowing air) in.....

 

[DogBunny]

I think you said you used a re-build kit. The float valves in most BS38 kits are crappy. Take a look at the needle and the seat under a magnifying glass, and you will see that they are poorly made and make a poor seal. You can and should buy genuine Mikuni float valves. This may not be your entire problem, but is probably at least contributing to it.

I still like my answer above. The float valves in the BS38 kits are crap. A good valve will never become "cocked" as you said yours did in one of your earlier posts.
Put your old Mikuni valves back in, or order some new ones if you already discarded them.

 

[DougXS2]

ha. funny you should say that.... when I found that valve loose enough to get cocked, I put the old valve back in and it does fit better. and I cant make it get cocked now so I feel confident that its not doing that anymore. and it does seem to be making a good seal when closed.... like I mentioned, when closed it will hold pressure with me blowing air into it....

so I'm guessing it not normal to overflow when parked and resting at an angle on the kick stand?

 

[DogBunny]

Leaking is never normal, but common with lousy valves, or if a speck of dust gets stuck in the valve seat, and it can't close.

I assume that you put the old Mikuni valve needle back in, AND you put the old Mikuni valve seat back in. If so, I'm stumped.

 

[gggGary]

How long was the tank seal job cured, brand of sealer? All new "tygon" or other reputable fuel lines? No matter how good the carb parts, and careful your work, crap from the rest of the fuel system can fuggle em.

 

[DougXS2]

I sealed the tank with Caswells Epoxy tank kit and it cured months before use. not sure of the fuel line brand but they are new 1/4 clear fuel rated line. New mikesxs petcocks (that work great and dont drip).

I did use the old needle but not the old seat. will try that next.

And I have no idea how the carbs worked before because it wasnt running when I got it.