Tank Vacuum, no Fuel Flow

[Tmycal]

My name is Tom, I'm out of Ventura, CA. I've been lurking for about 6 weeks, the same amount of time I've had my 1980 XS1100 standard (actually started as the venturer model). Thanks in large part to the help of the tech tips and knowledgeable responses in forums from members I now have my bike running great and in road worthy condition. Thank you all for that. Now there is one problem I have not quite figured out and I wanted to see what ideas some of you might have.

My model has the vacuum petcocks, which I rebuilt and when tested they work just fine. The problem arises when I'm actually riding the bike. I believe what happens is a vacuum great enough forms inside the tank which no longer allows fuel to flow from the petcocks, which cuts fuel to the carbs hence to the engine, dead stranded bike. I note this because after the engine cut out a few times while riding , and upon opening the fuel refill cap I can very obviously hear the vacuum being released. I've also ridden the bike with the cap not secured down and this fixes my problems, since the vacuum can't form with the cap open. Now I've checked the breather hose at the back end of the tank, blow air in and out with no issue so I don't think that is clogged or blocked.

I really don't want to keep riding with the cap loose, anyone have any ideas?

**I also wanted to note, I have clear inline filters from the petcocks to the carbs, so I can tell if there is fuel in the lines or not.

[vedgar]

tank cap vent plugged

Get a new cap or cleanthe existing one and your problem will be solved.
Vance

[natemoen]

No need to get a new cap.

The cap does come apart though and there is a little vent that needs to be cleaned out. When you take the cap apart there is a small hole that can be cleaned out and then there is also a small fiber disc and some foam like material. Those need to be cleaned up.

[wingnut]

The tube you mentioned at the back of the tank is just the overflow for the tank recess. all venting is done thru the cap. Good luck and congratulations on getting her running well

[Tmycal]

It's amusing, I'm often afraid to ask questions or attempt stubbornly to figure it out on my own. I can sit there and analyze something to death and the simplest solution might not pop in my head. (FYI I have an degree in engineering)

Thanks guys, I'll look at that cap first thing when I get home. Feeling a little silly right now

[vedgar]

need of help

Don,t worry about not knowing . I still have not figured out my low speed bog , I have been a licensed tech for 35 years.
Vance

[MPittma100]

Vent

It's amusing, I'm often afraid to ask questions or attempt stubbornly to figure it out on my own. I can sit there and analyze something to death and the simplest solution might not pop in my head. (FYI I have an degree in engineering)

Thanks guys, I'll look at that cap first thing when I get home. Feeling a little silly right now

Cleaning the cap vent is pretty straight forward. There are 3 small screws on the underside of the cap. The seal can also be replaced during this procedure. Replace seal if not in good shape. Cover the opening while disassembling cap - No need to fish for lost parts. Mikesxs.com is a source for the seals.

Mike

[natemoen]

Good pictures and step by step process here.

http://www.xs11.com/forum/showthread...ap+disassembly

[jetmechmarty]

There's a little filter in your cap. It rotted and plugged the vent hole. I made a new one out of a little piece of Scotch Brite.

[Tmycal]

Thanks to all who responded. This indeed was my problem. Also thanks for the lead on the seal, I'll be ordering one of those too.

Now I can enjoy some saddle time minus a jingling around gas cap and faint odor of fuel