Leaky Gas Cap Woes

[Ghostv2]

I have searched, but i am wanting some fresh input for this is sorta different.
The leaky cap is on the 200e, for comparison i am also posting a perfectly fine cap/tank for a 200s. I have tried to swap it over but it still leaks on the 200e and as you can see it is starting to ruin my tanks finish. I do not think its the rubber seal, because the seal is dried out just like the one on the 200s but that one still works fine. So could it be the tank? It leaks from multiple angles though, so it might be the seal. Maybe a trained eye can spot the problem.

First, the bad 200e.








Now, the good 200s tank/cap for comparison.





Sorry if its too many pictures but it couldnt hurt.
Like i said, i swapped the good cap over and it still leaked, am i missing something?

[El Camexican]

So basically regardless of which cap you use there is a leak? If I have that right I would take a good look at the rim, or lip of the leaking tank. Over all these years it is very possible that someone has jammed a gas pump hose into it and leaned on it or pulled it up and distorted it. You may not have had a leak back when the rubber cap seals were soft and pliable, but 30 years later they aren’t going to take up any voids.

The best way I know of to find defects in metal surfaces is to take a clean rag and fold it over a couple times. Then put your index finger on it and slowly go around the lip. If there is a defect you should feel it.

Another way you might try is to put a thin layer of grease on the lip of the tank and close the cap as careful as you can and then remove it and check to see if the grease transferred to the whole rubber gasket, or if a spot was missed. I’m not sure if your cap twists on, or if that tab in the middle is what locks it in place, so this might not work as well as I’m thinking.

Have fun.

PS. We now have your finger prints on file!

[fabiodriven]

Both of those gaskets look roached to me. I'd start there.

[Chopsaw]

All my caps are hard to turn . Hows that one ?
Leaks while riding or while parked ? Maybe its building pressure in the tank somehow .
The white grease would work I geuss if you just pushed the cap on and didn't twist it . Just dont get it in the tank .

[New2Tri-Z]

Both of those gaskets look roached to me. I'd start there.

x's 2, gaskets look smoked, try replacing that and see what happens.

[wonderboy]

I say look for an uneven flange on the tank. Do like already has been mentioned, or use a straightedge to try to figure if there is a low spot in the lip.

Just FYI, you can get a Honda replacement gas cap (the entire cap and gasket) new. It is part number 17620-HC3-505 and costs bout $40 (give or take).

The new gasket is part number 17631-899-000 and costs about $4.

[Thorpe]

Time for new a new rubber! (They dont last forever!)

[Ghostv2]

So basically regardless of which cap you use there is a leak? If I have that right I would take a good look at the rim, or lip of the leaking tank. Over all these years it is very possible that someone has jammed a gas pump hose into it and leaned on it or pulled it up and distorted it. You may not have had a leak back when the rubber cap seals were soft and pliable, but 30 years later they aren’t going to take up any voids.

The best way I know of to find defects in metal surfaces is to take a clean rag and fold it over a couple times. Then put your index finger on it and slowly go around the lip. If there is a defect you should feel it.

Another way you might try is to put a thin layer of grease on the lip of the tank and close the cap as careful as you can and then remove it and check to see if the grease transferred to the whole rubber gasket, or if a spot was missed. I’m not sure if your cap twists on, or if that tab in the middle is what locks it in place, so this might not work as well as I’m thinking.

Have fun.

PS. We now have your finger prints on file!

Sitting its fine, it only spills out when im riding becuase the gas is sloshing around when i go uphill or hit bumps. When its low on fuel its fine because the gas doesnt hit the top of the tank. Im thinking its more of the rim because of the fact my other one which i know is fine leaked on the big red. Ill have to check the rim and report back, i only stepped outside to take pictures to get another opinion.

I say look for an uneven flange on the tank. Do like already has been mentioned, or use a straightedge to try to figure if there is a low spot in the lip.

Just FYI, you can get a Honda replacement gas cap (the entire cap and gasket) new. It is part number 17620-HC3-505 and costs bout $40 (give or take).

The new gasket is part number 17631-899-000 and costs about $4.

I had no idea they still made them, are they a new style or the same ones?

I think regardless im going to try the new gasket idea, thats the obvious thing i should address. I just think its the rim or something else. Could it be leaking at the seam where the tank rolls under and goes into the rim? If that makes sense. Reference picture #3.

[wonderboy]

I had no idea they still made them, are they a new style or the same ones?

From the outside, they look identical. Underneath, they are a bit different. So, cosmetically you can't tell when you are riding. I'd take a picture of an original compared to the new one, but my machines are all tucked in for the winter back at my parents (couple hours away). Next time I get back there (maybe this weekend) I'll get some comparison pictures.

[Marty]

Spend the money and buy a new gas cap seal. All 3 of my 70's leaked but I spent the $9 on each gasket and now all 3 tanks are sealed and caps feel tight when taking off

[kebby28]

I went through this last spring with my 200es. The first thing I did was buy the $7 oem gasket but that didn't do it. I used a pair of channel locks and bent the rim up a little evenly all the way around... It still leaked. I had my buddy try bending the rim... still leaked. I got so sick of having gas dumping in my crotch I gave it one more shot and got it. Never leaked again. Just gotta keep trying till you get it.
I think maybe vacuum suck the rim in over the years?

[El Camexican]

Time for new a new rubber! (They dont last forever!)

Maybe not, but if you turn them inside out you can use them twice

[tri again]

Wish I could comment with real info but I really like the oem
gasket on the 87 es, it's almost like a pita pocket.
Seems like a rounded hollow tube that seals really nicely and no stress cracks.
Wonder if it would fit the older design? Seems to have twice the compressability.

The caps interchange from 85-87.

and what's the deal on stuff like transmission sealer leak stop?
Doesn't it swell rubber seals as a last ditch effort to stop leaks?
Maybe sopme of that would help...and probably cost more than a new gasket.
But like you said, your other cap, the known working non leaker doesn't cut it.

[El Camexican]

Wish I could comment with real info but I really like the oem
gasket on the 87 es, it's almost like a pita pocket.
Seems like a rounded hollow tube that seals really nicely and no stress cracks.
Wonder if it would fit the older design? Seems to have twice the compressability.

The caps interchange from 85-87.

I've heard that brake fluid softens rubber, but his gaskets are shot. If anything a chemical dip would make them fall apart.

On the topic of tanks I think Yamaha deserves a big for the plastic tanks they used on their YTM's The cross under tube, super strong plastic and cap on mine are still like new in every aspect. Honda may have had it over them in a lot of areas, but not with their metal fuel tanks.

[kb0nly]

I have been through this a few times....

Yes the gaskets are still available, Dr ATV has them, they are also on eBay, and even available OEM. Though i find the aftermarket ones are a smidge thicker than OEM and that helps.

Replace the rubber gasket, then you need to adjust the prongs on the cap that latch into the top of the tank. Those prongs ride around the underneath of the opening, the problem is the on and off all the time wears down the underside of the lip, and wears into the prongs on the cap. Carefully bend the tabs towards the top of the cap a little bit, usually i just tap them lightly a few times with a small ball peen . That should make the cap pull down tighter, these caps should be damn snug when you put them on, if its really easy to put on and turn they are NOT tight enough.

The other thing i do is take the same small ball peen and tap down the inner edge of the opening from the tab slot to about 90 degrees from it. This is a bit hard to explain but you turn the cap clockwise, so start at one of the slots and go clockwise from it and tap down the inner edge just a tiny bit until your 90 degrees from the slot, do that on both sides for both slots, basically just light taps, then test fit, then do it again, etc.

You want the inner edges bottom down in the tank farther so the tab rides down under it and pulls the cap down tighter on the top edge. That make sense? A new rubber seal and a little time with the peen and i can make them seal every time. Depending on how often you take the cap on and off you might have to tighten them back up a couple times a year. The only other fix is to weld extra thickness to the tabs on the cap or get a brand new cap. Usually it wears a groove into the top side of the caps tabs which makes the cap looser and then you get leaks.