Special Petcock Mod

[fredintoon]

Fred, the more I work on these bikes, the more I wonder at some of the design decisions Yamaha made...

Hi Steve,
I think it's about department compartmentalism. I moved from an XS650 to an XS11 and almost everything about the design of those two bikes is different.
Not so much the 2 vs 4 cylinders or chain vs shaft but the little things like the swingarm pivot; plastic bushings vs sealed bearings; or the seat hold down, keyed latch vs having to carry a 14mm long socket & ratchet.
I see two design offices that share a common parts catalog but are forbidden to talk to each other.

[crazy steve]

Yeah, but you'd think the bean counters who generally oversee these guys would ask why they're spending money on additional tooling, inventory, and install training...

But the Japanese do love 'new', even when it makes no sense to occidental eyes, so maybe it's a cultural thing.

Like I said, it makes me wonder, but there's not much I can do about it...

[BigDick]

???? I have an 80 special, no octy, didn't need to do this. Fuel only flows when the petcocks are up (reserve position) and only from the rear port.

[Ebenezer]

I think this is a great idea and will do it this weekend when I rebuild my petcocks. Where did you find the rubber cap for the prime spigot?

[crazy steve]

I think this is a great idea and will do it this weekend when I rebuild my petcocks. Where did you find the rubber cap for the prime spigot?

Auto parts store vacuum line cap for 1/4". It was a bit long, I shortened it maybe a 1/2"....

[windjammergump]

peccocks

mine first and only 81 special (1100) has the prime tubes filled with silicon and dryed hard....i am fixin to change them but it worked and the silicon could be removed later if needed ,,,,but i am having carb issues so dont know if it has anything to do with the silicon...some enstein...put a wood screw in the vent of my gascap....also....it is a next rebuild in the future

[ViperRon]

Lack of appreciation

Great information Steve as usual. Its so cheap and simple some here apparently can not wrap their mind arround it. I personally have seen on more than a few the failure of the petcock to stop flowing fuel and fill the cylinders full after sitting a few days. It really does not take much wear or build-up for the float valves to hang open. You can be adjusted perfect on float level and bike have run perfect for months and then you shut it off put it in the shed having sweet dreams of your ride that night. A week or so latter the nightmare begins as the puddle of gas, paint warping on engine parts, airfilter box soaked, and a crankcase full of gas destroying the 3 quarts of 9.00 per can oil and 15.00 filter tell you your ride is done today.

Better yet you never even notice that gas leaked down each ride and has basically evaporated out of the crankcase after destroying the oil. In a few months you are rebuilding your baby.

Thanks

[cywelchjr]

Auto parts store vacuum line cap for 1/4". It was a bit long, I shortened it maybe a 1/2"....

I'd be worried about how that might stand up to gas. It might be safer to just do as some suggest and to connect the two together with a length of fuel line, then no leak and you know it will handle any fuel that might get in there.

[crazy steve]

I'd be worried about how that might stand up to gas...

This is the mod Cy, and that cap is just there for trim.... it won't ever see gas...

[neJeff]

Steve, Is the tap a 5.8mm or a 5mm and how exactly does the set screw stop the flow to the primary.

[crazy steve]

It's a 5mm, .8 thread pitch. The various holes you see behind the lever corrospond to the lever positions. The hole below the 'blank' on each petcock is where fuel comes through when the lever is turned to 'prime'.

The screw plugs the hole....

[neJeff]

Thanks Steve. I am going to wait until the end of the season and then do it.

[DGXSER]

Viper Ron, If your having fuel flowing out your carbs when you let the bike sit, then you have carb issues that will not be cured by messing round with the petcocks. You need to clean and or replace your float valves or figure out why your floats are not floating.

The petcock modification simply seals off the prime setting. You had an off all along, and if you leave them in the ON position then this mod changed nothing for you. If you still have the OCTY then it may also need attention, but your float valves are the real "gate keepers" of when fuel does or does not flow into your carbs, and when they do not do their job well, into your airbox and or engine.

[neJeff]

Steve, Did the de-octy this morning and although I had to re-route twice to get flow going its working fine...I did however goof something up as it only gets gas on primary. Will do your mod this winter. I used vinyl tubing as I knew it would be coming off in a few months (and the hardware store was out of gas line) , shouldn't cause any problems, right?

[crazy steve]

...I used vinyl tubing as I knew it would be coming off in a few months (and the hardware store was out of gas line) , shouldn't cause any problems, right?

Watch that line like a hawk, as some vinyl tube will soften/swell under exposure to gas/solvents and fail. Wouldn't want to see anybody trying to do a Nick Cage 'ghost rider' imitation...