Vacume Control Fuel

[wingnut]

OK maybe this is just the mussing of a student at the feet of the masters but… What were our little friends from across the big pond thinking with the vacuum controlled fuel system? Was it because it was a trick way to keep those Marconi carbs from filling the floor of our garages with fuel if we forgot to close the petcocks, EPA mandated control of hydrocarbon vapors or was it something else? I really can’t see an advantage to a system like this when manual valves are so reliable and inexpensive. Now to the meat of my ramblings, how many special drivers have kept the factory fuel line set up? First the need for additional in line filters and the lack of available space to install them almost forces us to get creative. Given 2 petcocks that do not leak (requires some effort), why not tee (a Y fitting would work even better) both lines from the valve to the inline and then straight to the carb inlet. Removing the octopus also opens the area up for better access to the number 1&2 carbs plus makes hooking the monometer up simpler during tuning. The standard riders have fewer options due to the valves and upper vent tees but the special drivers do. Getting rid of excess tubing from that area of the engine sounds like a good idea to me. Especially tubing that’s carrying fuel. I would like to hear the group’s thoughts.

[Targetman]

Maybe it's because if the bike is in an accident, the engine stops because of the tip-over switch, dead engine=no vacuum.
No vacuum means gas stays in tank.
Does that sound right?
Or will it just come out of the filler anyway?
Just guessing. I haven't tested this theory (on this bike) yet!

[Ken Talbot]

I just look at it as a 'modern convenience'. I've got two standards and two specials, and all of the vacuum control bits work the way they're supposed to. Yes, it has taken a bit of maintenance but that's to be expected on something that is 25 years old. I like being able to hop on the bike and ride off without having to think about turning on the fuel, and I like to stop, get off, and walk away without having to remember to shut the fuel off. I also like knowing that my headlight comes on automatically, that I will automatically have a back-up headlight operating if my low-beam burns out, and that my signals will cancel themselves after an appropriate amount of time. Yeah, I know none of this stuff takes a lot of effort to do manually, but I just like it.

TMSAISTI....

[Pat Kelly]

My E still has the vacuum petcocks (currently having issues with them).
My LG has the octopus removed and they are manual. I ran each petcock to it's own 'T', connected the 'T's so that all 4 carbs run off either or both petcocks.

[wingnut]

Safety

Target I can see the safety issue. But the fuel in all those lines, down stream, from the octopus is going to run to the lowest carb and out of the air box. It would stop the whole tank from pouring out but there is still plenty to leak. Better than nothing I guess. I don’t want to sound like a paranoid but after reading yours and Ken’s responses I can believe it was a mandated attempt to make the bike safer. Insurance industry pressure and government regulations might have pressured the manufacturer to incorporate these features. The automatic headlights and vacuum canceling fuel system might have been attempts to keep us safe from ourselves. I also like the head light feature and the modern conveniences. The light system is great in fact I’m trying to figure more ways of being visible, but I’m with Pat the octopus goes.

[LoserShoes]

The fuel doesn't drain out of the lines if the petcock works correctly. Put your finger over the end of a straw in liquid and pull the straw out. How much of liquid drains out? None. Needs a vent on top to drain.

Steve

[mikeb]

I still have the factory octapus and have had very little problems with it. When I rebuilt my carbs after their 17 year slumber I got a rebuild kit for the octapus valve. As many have discovered the plunger was too short and would not seal so I replaced the o-ring on the old one and stretched the spring about and eighth of an inch and have had no problems. As for why they used this setup I'm not sure but probably for liability reasons. After alot of people forgot to shut off the fuel and dumped gas all over the garage, there were probably law suits filed and this was a solution to the problem. Just a guess but it wouldn't take many garages burning down to force a change.

[jeffe]

My 78E is the second bike I've had with the vacuum petcocks. Never had any problem with either bike. Other bike was XJ650RJ, or a 1982 650 Seca. Had somewhere over 75,000k miles on it and never had a minutes trouble.

I know that the vacuum petcocks on my 78E saved me a lot of grief untill I figured out that the number 3 carb float had a leak and wouldn't shut off. Don't ask how long this process took.

[jeffe]

Forgot to say that when I got my 78E i just took them apart and cleaned them, nothing else needed done.

[JWSanders]

I've been debating taking out my octopus as well, if anything just to make it look cleaner in that area. It's always worked for me though. Still has the original seal in it.

[edgo]

I had to rebuild and re-jet my carbs so I ditched the octopus just because it was a pain to take off the carbs with it installed. I capped off the "run" side of the petcock and just use "reserve" all the time. I have to reset the odometer at every fill up since I don't trust the low fuel light but the light is working. As a former motocrosser it's a reflex for me to work the petcock when I get on or off the bike.

Ed

[John]

You may want to check which nipple of the petcock you have the fuel line attached to. The rear ward nipple is for the run and reserve mode. The forward nipple is for prime, and prime won't be needed when you remove the octopus. Cap it off. By running on the forward (prime)nipple you are eliminating the reserve function, as the prime side of the petcock uses the reserve section of the pickup tubes, which sit lower in the tank. When you think you are switching to reserve, it won't be there as you have been running on it all the time. I have removed my octopus years ago, and the way I have the lines plumbed, I can run on one petcock at a time or both at once if I want. I only use one petcock though. I have not had a fuel supply problem at all, and if I want to really twist up on it, I just open the second petcock to be safe. The run position on these petcocks is with the handle down, and reserve is handle up. handle pointed forward is off. I have been doing this for so long, that turning the fuel off and on is easier to remember than... say...putting up the kick stand.

[edgo]

Thanks John. I have my line on each side hooked up to the front petcock tube and I always turn it to "res" from "off" to get going. So will it run set to "on" with a full tank? I guess I should try that. I thought I was capping off the "pri".

Ed

[rickmcdougald]

Hey MikeB, where'd you get that kit?

Please.
RLMcD