Hi all, just a couple of questions about fuel cap sealing.... I filled up my RS very full, and ended up stopping after very little distance, put it on the side stand, and then noticed I was leaking fuel. OK - I won't use the side stand when tank completely full! But was surprised by the ease of leak. So, thinking about whether my cap is too leaky, I can replace the old seal, but: -I notice the cap has what is presumably a vent hole, ones in the centre piece, and ones on the outer cap (seen in photo). Will fuel always leak out of these, or is there supposed to be some sort of valve in it? Or is it just positioned such that you wouldn't expect fuel to get out even on side stand? (I guess I could replace the whole cap, or test the venting) -I notice under my old rubber seal, which I will replace anyway, there is a clear harder plastic ring (I'm holding it in second photo). This seems unlikely to help sealing.... it's not soft like rubber. I can't see this on parts diagrams. Is it supposed to be there? Is it present on other peoples bikes? I'm thinking about removing it.... is that a bad idea? It might be to help the cap rotate when removing? Thanks for any tips! Quite possible just replacing the rubber seal is all I need to do anyway (it looks bad in photos, but I thought the actual sealing bit wasn't cracked, but no harm replacing). I note, I also realised my side stand had lost it's retaining nut, so was a bit loose, so bike may have been leant over slightly further than normal. But still suprised to see petrol flowing out....
Definately replace that seal ... I ususlly turn them over but that is shot Are u overfilling it? .... shouldnt come above the bottom of the 'neck' https://www.cmsnl.com/honda-cb250rs-1980-a-england_model16355/packing-fuel-cap_17632422000/
Ha, thanks! Yes the seal will be replaced. I think the bit that actually gets squashed and seals isn't cracked, but totally agree, time for a new one. Yes I probably am overfilling.... always tempting to squeeze a little more in. Based on that, maybe it is expected that fuel would leak out the vents in the cap if overfilled? I'm still curious about the extra clear plastic washer.... there is no sign of it in parts lists: https://www.cmsnl.com/honda-cb250rs-1980-a-england_model16355/partslist/F13.html but maybe it is part of the cap.
I have seen the plastic washer on other fuel caps, as you said to help the rubber slip when turning. Leave it there, it will help with sealing, and don't overfill the tank.
Check the breathers for the cap, if the tank has them. There may be one or two drain holes leading to the bottom of the tank where drain hoses attach. Often they can become blocked. One will be around the cap area, one will be internal to fuel tank in case of overfilling. Blow them out from the bottom of the tank with compressed air.
