Topic: Carb float buoyancy test?

[mgilvary]

I seem to remember reading somewhere about a way to test your floats to ensure they are still buoyant. I did a search on this, but couldn't find anything. Is it as simple as dropping them in some gasoline and seeing if they float? Or is there some way to measure the degree of buoyancy?

Semi-related carb question, which I can't seem to find the answer to: When adjusting the air screw, which way makes the mix leaner, and which way richer? If it makes a difference, I'm asking about a '75 550.

[Steve F]

Simply dropping the floats in gas will indicate if they float, but you also need to submenrge them and look for bubbles.  Also shaking them by your ear to listen for gas sloshing around may be a good indication they have holes.
To adjust the idle mixture, remember which "side" of the carburetor the screw is at. In other words, if the screw is closer to the air filter, then you're adjusting the "air".  If the screw is closer to the engine, then you're adjusting the fuel.  IN is less, OUT is more.  IN=less air or fuel  OUT=more air or fuel.  Now that I got you TOTALLY confused..... 

[TwoTired]

The 75 CB550 (both F and K models) have Idle Air Screws.  Turning clockwise makes a richer mixture, anti-clockwise, a leaner mixture.

Turn them out equally across the bank, until you can't stand the low speed throttle response.  Then turn them back in a bit until you can.

[mgilvary]

Thanks for the primer on the air screw, guys.

On the float -- mine are the rubber type, not brass. Are they known to lose buoyancy over time?

[TwoTired]

Thanks for the primer on the air screw, guys.

On the float -- mine are the rubber type, not brass. Are they known to lose buoyancy over time?

Not that I have experienced.  But, agressive carb cleaners could certainly effect them.  Do they look..dissolved?

[Geeto67]

if you don't want to be standing around over an open container of gasoline just use water to test your floats. I usually drop mine in a big gulp cup filled with water, if they float it's all good. Also submerge them and look for bubbles. if there is a hole you can usually steam the water out by heating the float slightly and then fill the hole (if it is small enough) with some solder for brass floats.

Because of the effects of gasoline if your rubber floats were ever in gas and then let to sit in bad gas they can crack and decompose. Personally if you can get replacement rubber anything it is usually worth the piece of mind. Don't use carb cleaner on them. Soak them in warm water to make the pliable and then evaluate. if you press them and they start to show cracks then replace. The rubber floats go bad when they dry rot and then gas gets in the cracks causing small amounts of gas to become trapped and saturate the float (making it heavier than it should be).

weren't there also plastic floats used on some bikes?

[mgilvary]

Do they look..dissolved?

No, they look pretty good, actually. I ask because I seem to have ongoing, intermittent overflow problems -- even with brand new needles/seats -- and am just trying to think through all the possibilities.

[TwoTired]

Well, I must admit that all of my CB550's do that from time to time.  It's why I have the habit of turning off the petcock. But, unless there's been fuel contamination bits blocking the float valve, it has never occurred while parked on the center stand.  My theory is that there is some side loading friction on the float pivots, when the side stand is used.  But, it's never annoyed me enough to go quash that gremlin.  Perhaps I'm overly tolerant due to having a BSA twin years ago.

I did have a set of carbs that were chronic floor wetters though.  Turned out that when a PO rebuilt them before, they left nasty plier teeth marks on the pivot pins.  This apparently created enough extra friction to hinder the swing and closure of the float valve.    I polished out the tool marks and they were much better.

[mgilvary]

Interesting. At least one of my pins has plier marks on it -- enough to make it stick solid in the holder, although the float seems to pivot okay.

Next time I have the carbs off, I think I'll polish all of the pins, make sure they're nice and slippery.