Leaky carbs

[letxbruce]

My 79 CBX as well as 80 FLT have done this for years. A little leak off right after they are parked, then tight for weeks after. I think this would rule out the leaky float possibility. I first thought it may be the ethanol vaporizing then condensing, but after a little research I found that our pump gasoline has such a low vapor pressure now days that it has to be reformulated for summer consumption so it doesn't start to boil at 100 degrees F in the fuel tank! This summer blend uses more expensive additives, hence the typical increase in gas prices during the summer. The floats on the parked CBX are warmed by heat radiating from the block enough to easily boil either blend. I suppose these fumes then could condense in the overflow tubes which would not conduct heat as well as the aluminum float bowls. Anyway, I always leave the garage door open long enough to air out the puked fumes, then never have any problem once everything has cooled down.
Here is the link that I found:

http://www.eprinc.org/pdf/primerongasolineblending.pdf

[Kool_Biker]

I couldn't agree more!

[Randakk]

After every ride and upon my return, my Z will ALWAYS discharge a few cc's of unburned fuel onto the garage floor through the overflow tube.
It will never leak more, and it will NOT do this with the engine cold and the fuel tap in the 'on' position (no vacuum valve in my Z).

Do you think the state of the float valves (1 to 3 shown here, the others very similar) below, could explain this ???? They look good enough to me.
I have a new set but would like to know your opinion before I replace them.

P1090774.jpg

Please be aware of the magnification here.

Best, Aris

I see clear "issues" with those float valves. I would replace them with OEM Honda float valves.

I don't recommend "wet testing" of float valves because it's hazardous for amateurs and largely an unnecessary step. And the results of such testing are not 100% reliable. Such testing will yield some "false negatives" since it eliminates the useful vibration of a running engine...an aid to float valve sealing and a design consideration.

Depending on the test protocol, "false positives" can happen as well.

This all points to why a functional petcock is necessary....non-running engines don't control the flow of fuel through the float valves quite as well as running engines.

I've never had a single new Honda float valve (my recommendation) fail on initial start-up when properly installed and float operation checked and adjusted to spec. Actually, I've never had a single carb leak of any type actually when using all new rubber parts during a rebuild (my recommendation).

As noted above, the overflow "standpipes" should be checked carefully. I don't believe that is your issue.

[Mike Nixon]

The stock float valves, as good as they ae (and they are *worlds* better than anything else out there) still need to be replaced from time to time. They're not permanent parts. And looking at them isn't enough. Vacuum test them. Remove the seats and attach a Mityvac to each seat, with a drop of WD40 on each valve, test it individually in its seat. The float valve hardens over time, so tha even a good visual will still leak as it is less able to conform to the seat. Speaking of the seat, the seats get grungy, so clean them with a cotton swab dipped in carb aerosol. Do *not* burnish the seats with toothpaste or any other abrasive. After many hundreds of rebuilds, I no longer second-guess float valves but replace them each and every time, only with stock, the rest don't come close.

[bobber01]

The stock float valves, as good as they ae (and they are *worlds* better than anything else out there) still need to be replaced from time to time. They're not permanent parts. And looking at them isn't enough. Vacuum test them. Remove the seats and attach a Mityvac to each seat, with a drop of WD40 on each valve, test it individually in its seat. The float valve hardens over time, so tha even a good visual will still leak as it is less able to conform to the seat. Speaking of the seat, the seats get grungy, so clean them with a cotton swab dipped in carb aerosol. Do *not* burnish the seats with toothpaste or any other abrasive. After many hundreds of rebuilds, I no longer second-guess float valves but replace them each and every time, only with stock, the rest don't come close.

Never thought or heard of a 'vacuum test' on float valves but what a great idea. Thank you for the tip. Don't have a Mityvac but do have many 60cc syringes/tubing which will do the job I think.