CB750K2 petrol tank not venting

[sprinta]

Having a problem which I suspect is due to the petrol tank not venting properly?

Went for a ride yesterday and parked the bike for a while, fairly sunny and warm day. However, when I restarted the bike it kept stalling, managed to get going having to rev it higher to stop it stalling but then started jerking and missing and would not pick up, went to reserve no changed then it just expired and came to a halt, very much like running out of petrol?

Lifted the petrol cap, helmet and ear plugs in so could not hear anything and then the bike started and ran home OK.

This morning I opened the cap and there was a distinct sudden rush of air into the tank, so suspect that the cap is not allowing air in and/or not venting properly?

It is an after market Yamiya cap so took it apart to find all vent holes clear. However, is it possible that it was not correctly assembled?

With reference to the attached does anybody have a Yamiya cap that they could check to see what the correct assembly is for the internal rubber gasket.

The 1st one is how it was when I took it apart or should it be as the second photo?

The small o-ring just appeared when I took it apart so I have assumed that is it's correct placement, which may not be correct?

[philward]

From distant past, I seem to remember having the same problem with an aftermarket cap (although not Yamaya). Seemed to remember having to drill the vent hole out as it was blocked

[sprinta]

Thanks for your reply.

However, all the vent holes were clear which is why I was looking at if the internal rubber gasket had originally been fitted the right way round.

Hoping that somebody may also have one of the Yamiya caps and could check their and let me know which is the correct way round, as the first or second photo?

[Trigger]

I would try it both ways and see the results or contact Yamiya. These days i use the genuine cap from the 500four 17510-323-310 which comes as a sealed unit. Sorry can not help 

[McCabe-Thiele (Ted)]

Can't you just pucker your lips & blow into the cap from the underside to simply test it?

[paul G]

Can't you just pucker your lips & blow into the cap from the underside to simply test it?

I have seen a few women that could 

[Trigger]

Julie was filling up with fuel today and i noticed that her cap on her mongrel had a non sealed cap and is a aftermarket one. Took it apart but, it looks very simple compared to yours .





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[sprinta]

Thanks Graham

If you carefully peel away the outer gasket it will separate the two plates and you should then see the inner gasket and smaller plate. Could take a photo of it and that would hopefully show if it is as my 1st or 2nd photo and therefore, which one should assume it the correct way.

Have you come across the small o-ring? you may find it between the two plate which would also locate its position?

[sprinta]

Can't you just pucker your lips & blow into the cap from the underside to simply test it?

Have tried that, but it is not very conclusive one way or the other.

[Trigger]

No o'ring and looks like this .




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[sprinta]

Thanks Graham.

That shows mine was the same way when I took it apart, so it was correctly assembled and therefore not the likely cause for mine seemingly not venting?

Not sure as to if the small o-ring on mine has any relevance and may just have been fitted on the screw so that if it unwound it would not fall out?

Thanks for your help, much appreciated.

[Trigger]

I did notice that when i took the cap apart that, all 3 plates have a vent hole in them and all were inline with each other 

[sprinta]

Thanks, that's something that I can do as I did stagger them. Grasping at straws possibly, but worth a try.