Dual Petcocks

[Ole Blue 73]

I just purchased a really clean 1973 TX650 and am just getting familiar with it. Ran perfect on the test ride, but later just running (poorly) on one cylinder. Pulled the tank to check the wiring and it wouldn't come loose. I'll be, there is a second petcock on the other side. Each petcock feeds one carburetor and the fuel lines are a bit short. I'm guessing it will run a lot better if you turn on fuel to both carbs. Now, should I put tees in the fuel lines so it will feed both carbs from either side or is this just greatly increasing the opportunity for fuel leaks? Is best practice to just pull your head out and turn on both petcocks if you want to go for a ride?

 

[Jim]

Welcome to the forum!!

The stock BS38's should (already) have a crossover tube (red oval).


Image courtesy @Mailman

 

[Ole Blue 73]

My bad - this bike has a pair of Mikuni VM34s that are a bit different than stock. I do have the original carbs in a box that came with the bike as well as the points system. Now running Boyer Bransden electronic ignition.

 

[Jim]

No worries.

If it were me, I'd just leave it be. Now you know, I doubt you'll forget again. Not for long anyway.

 

[Jim]

We love pictures here....

 

[toglhot]

You meed to turn on both petcocks, with any carbs, that's why there are two. If it ran Ok before with just one petcock on, then it must already have a T piece linking both carbs, or some other means of linking them. Without a link and only one petcock on, only one cylinder will run, the other is not getting any fuel.
It's a good idea to link the carbs anyway, because without linking them and with both petcocks on, one carb may starve when the fuel level in the tank gets below the tunnel.

 

[Jim]

The tunnel on these tanks slopes down at the back. Down to within an inch or less from the bottom of the tank at the far rear. When that bit runs dry, there's precious little fuel left to get trapped...prolly only a cupful or two. So that's not really a concern on our XS'

 

[toglhot]

Whilst the fuel below the tunnel is a very small amount, it may help if stuck in the middle of nowhere. Also helps syncing when the fuel is low. I found that out recently: Peered in the tank and sloshed fuel around, seemed there was plenty in there for syncing, but one side was empty. Very difficult syncing carbs when one is starving, I originally used T pieces to level both sides of the tank and adapters for linking 6mm to 8mm fuel hoses. VMs have an 8mm inlet spigot. But that was awfully untidy and had to be unplugged whenever I lifted the tank. So I made this distributor, when lifting the tank you just have to disconnect the petcock lines. Both carbs are now fed down to the last drop.
Another option is to install a fuel level gauge, so you always know how much fuel you have. Some bikes have them standard.

 

[gggGary]

Late one night on the freeway tipping a honda CL77 over towards the single petcock nose of the bike up, got the engine started and made it five miles to a gas station.

 

[nj1639]

Late one night on the freeway tipping a honda CL77 over towards the single petcock nose of the bike up, got the engine started and made it five miles to a gas station.

In that vein, thinking when I ran a '78 Standard tank on me old '83 HS single petcock feed bs34's, right side petcock opening on the tank blanked off, there was a reserve 'reserve' on the right side for just such occasions. Nice unexpected feature.