Gas Cap Blues....

[teazer]

Sounds like the vented caps are not as "open" as say a TZ tank vent. That's good to hear. Presumably there is a less direct path for fuel to slosh out of that with a road racer. That makes perfect sense.

[LOUD MOUSE]

My RACE BIKES (1973 125 ELSINOR AND 1975 YZ 250) had vent tubes and no valves or leaking gas ever. Look at what it may take to vent air and not gas at the cap and ya can understand things which are OLD HAT to others. ..........lm

Sounds like the vented caps are not as "open" as say a TZ tank vent. That's good to hear. Presumably there is a less direct path for fuel to slosh out of that with a road racer. That makes perfect sense.

[CliffC]

Vince,
Road racing early '60s, CB72 and 77 stock tanks. Took the stock cap, drilled 1/4 inch hole in the middle and brazed a 1/4 inch tube to the cap and painted same as tank, you could chrome if you wanted. The tube was straight up about a 1/2 inch than bent 90 degrees and was 1 1/2 inch long. We brazed to the cap so it was facing straight forward when cap was on tight. I don't remember ever having any fuel coming coming out of the tube. Cliff

[Vince Lupo]

Wow - this cap has generated a lot of interest!

Okay, so here's another annoying question (aren't mine always???): If I didn't want to remove my steering damper knob arrangement (because I kinda like it), would it be reasonable/safe for the tube to route underneath the channel on the underside of the tank and just kinda sit there? Or would that not be a good idea?

I've surveyed my friends who also have Dreams and SuperHawks, and they too report wet gaskets when they remove the caps on their tanks. So either we all have clogged vents, or this was an unfortunate design flaw in this cap? Does this happen with everyone else's gas caps?

I suppose the only other consideration with this new cap/tube arrangement is when I want to use a tank bag on the bike, but I'm sure I can work around that when the time comes.

[teazer]

LM, thanks for that enlightening reply.

I do realize that we are talking slow old Hondas here and not a road race bike and I realize that your old dirt bikes don't brake as hard a road racer. They do bounce up and down a damn site harder though. I also understand that breathing through the cap is a less direct path than say a breather mounted straight into the tank top near the front.

My CB72 didn't have any issues with leakage through the breather hole in the cap of either tank I used, but with a stock tank and larger hole on a CB160 we get a small amount of fuel on the top through the breather especially with a full tank.

Vince,
If the breather cap were blocked and the cap were sealing perfectly, the bike would run out of gas in the float bowls very quickly. Gas on that surface is either a poor seal or just the fuel sloshing up against the cap.

With most of the Honda caps there is a tiny hole on the underside just outside of where the rubber/cork sealing ring sits. Sometimes if the cap is blocked, it may be useful to drill another hole from below, but only through the first (lower) skin. You don't need to drill all the way through the top surface.

[davomoto]

Vince, i would try to route the hose forward of the tank, which sits atop the engine. I fgas should come out, say in a tip over, hot engines and gasoline are not a good combo. If you're really set on running it under the tank, definately install a one way valve. Any dealer should have them, small pastic item with a nipple on both ends.

davomoto

[LOUD MOUSE]

You are welcome.
BTW it's normal today to have the paint peal back at the tank opening even with a NOS replacement cap (HONDA ISSUE) as the gas will (always has) wet the seal whether the CORK early issue or the RUBBER current issue.
My sort of cure is to NOT paint the seal area just leave bare steel.
The steel gets wet (can't see it anyway) but the paint edge (not getting wet) will USUALLY NOT curl back/up.
I did this the first time when I experienced the gas as we get today if dripped and not cleaned quickly would peal the paint if ya hadn't applied a GOOD clear coat over the color.
Today's darn gas even peals/damages the Dupont IMRON I use................lm

LM, thanks for that enlightening reply.

I do realize that we are talking slow old Hondas here and not a road race bike and I realize that your old dirt bikes don't brake as hard a road racer. They do bounce up and down a damn site harder though. I also understand that breathing through the cap is a less direct path than say a breather mounted straight into the tank top near the front.

My CB72 didn't have any issues with leakage through the breather hole in the cap of either tank I used, but with a stock tank and larger hole on a CB160 we get a small amount of fuel on the top through the breather especially with a full tank.

Vince,
If the breather cap were blocked and the cap were sealing perfectly, the bike would run out of gas in the float bowls very quickly. Gas on that surface is either a poor seal or just the fuel sloshing up against the cap.

With most of the Honda caps there is a tiny hole on the underside just outside of where the rubber/cork sealing ring sits. Sometimes if the cap is blocked, it may be useful to drill another hole from below, but only through the first (lower) skin. You don't need to drill all the way through the top surface.