My naughty carb

[Primate]

Is is peeing everywhere--in front of cars, bikes, with no shame. Not sure why it happened so suddenly. When it 's leaking, it's POURING, at the rate gas pours through the open petcock. This is what I've done so far:

-Checked the float. They floated in gasoline, and didn't bubble when submerged, so I'm guessing they're OK. Shook them--nothing inside (are they hollow?)

-Adjusted the tab on the floats up to close the valve sooner.

-Inspected the float valve. The pointed part is smooth and not worn or notched. The spring loaded ball on the bottom seems fine, and the spring resistance is no different from the one on the other side.

-Have tried to see if the floats get caught or for any reason can't move freely up and down, but haven't seen anything funky.

The funny thing is it happened so suddenly, which I would think is some sort of total failure, but I can't see anything abnormal compared to the other (good) one. The first fix (bending the float tab up) was good for a day, but the pouring came back when I pulled into my driveway coming back from work. There was no leaking before that--I checked every time I hit a stop sign or red light. What else should I be looking at?

Tahnks all.

[Ken in Oklahoma]

-Checked the float. They floated in gasoline, and didn't bubble when submerged, so I'm guessing they're OK. Shook them--nothing inside (are they hollow?)

Floating in gas isn't a good enough check. I chased my tail for months on my first airhead (R100/7) trying to keep the damned gas inside the float bowl. I fine tuned the (theoretical) float height by turning the gas on and holding the float up with the fingers and then dropping the float to see when the needle let gas through. Several times I thought I had gotten it just right only to end up with a wet shoe or wet asphalt.

In desperation I finally tried new floats. Set the height per spec, and damned if the dribble didn't go away.

Digital scales (often found in office supply stores) allow me to compare a new float with my old floats. The difference in weight was dramatic. (Sorry I didn't record any actual figures.)

I now stock a new pair of floats for the time when one of my airheads starts dribbling. I'll weigh the new and old floats first and if the difference is significant I'll pop in the new floats. (Floats plural because if one is heavy its partner is likely to be heavy too.)


Ken

[Deleted User 287]

I haven't been following everything you have been doing primate, but have you replaced the fuel line? Or at least check to see if that is where your leak might be. Happened to me once.

[SteveD]

You haven't mentioned letting the petrol run with the bowl off, whilst jiggling the float up and down. If there is junk on the seat where the float needle should close the flow, it won't close correctly. The hoses can deteriorate or junk from the tank gets stuck. Catch the flow and inspect what flushes thru.

If this solves your problem, then it may be time for new lines +/- an inline filter and a flush of the tank, with taps off. There's a chance the seat will need replacing too I s'pose.

[chasbmw]

By adjusting the tab on the float you are altering the float height and suddenly you will find that the bike won't pull over 65mph............

Steve's advice is good.

[Primate]

Thanks Ken, I'll start by weighing the two float assemblies, and look for any differences. Will also check for any junk coming out of the lines, Steve.

And chasbmw, that was a problem I'd already experienced a while back for another reason, but fortunately no fuel starvation yesterday, and I was cruising at freeway speeds (75-80 mph here in California ) for about 20 minutes each way, nary a hiccup, but thanks.

More later.

[Major Softie]

Snowbum says new 1-piece floats weigh 13 grams. An 18 gram float will barely float at all.

[Jean]

If you've never replaced the floats, this is most likely where the problem is...HOWEVER, do check the fuel lines at every connection to be sure you don't have a leak somewhere else.
Maybe you should install a couple of little clear filters in your gas lines in the event there is crud coming our of your gas tank.
Did I miss where you mentioned what bike this is and how old...???

[Primate]

Thank you, Major, for that info. I was going to ask around for that, much appreciated. I'll dig into the carbs and weigh them tonight ( when the garage temp is below 100-- we're having a little heat spell out here now). The floats are dark yellow with copper colored blotches all over. Probably pretty old, so . . .

Been thinking about that, Jean, but about leaks elsewhere, naw, it's OK everywhere else. Thor is a '74 R90/6, which I bought a little over a year ago. The previous owner didn't seem to care much about its upkeep--at least 3 previous owners according to the guy I bought it off.

Thanks all.

[Primate]

Weighed both floats. The one from the good carb is 13 grams; the leaky side one is 15. Ordered a new one.

Now, back to one question I buried in my first post: are these things hollow? Because if they are, just for the hell of it, what would happen if I shaved a bit off the sides or drilled some holes in the heavy one to lighten it? If it's hollow, the result would be obvious, but if it's hollow . . .

I'll do some experimenting when the new one comes in.