Fuel banjos

marshg246 said:
the ID of the 1/4" banjos is around 1/8".
Click to expand...

The spare 1/4" banjos I have are larger than 1/8" and closer to 5/32" (0.156").

marshg246 said:
Also, I've re-read several Triumph Owner's manuals and have no found none that says to open both taps. Please state what manual says that if Triumph was implied.
Click to expand...

Same as TT posted for other years of T140.
 
Triton Thrasher said:
1978 750 handbook.

Fuel banjos


Click to expand...
Pretty sure that uses 1/4". Any before NVT?
 
As a point of reference, my Atlas has but one fuel tap in the tank. I use 1/4" auto parts store tubing and a scintered bronze filter. It does not run lean on the top so far as I can tell. 230 main jets.

However I did have a lean running condition when there was a kink in the line from being too short after I installed the filter. It would only falter going up a slight grade into the wind but coming back the same road was no problem. The hose was not obviously kinked. I changed needle settings to no avail, then thought about it for a while and the solution came to me as I wicked it on up the hill passing the fire station wanting to impress a friend who works there. It stumbled and crapped out as the float level dropped.
 
Another factor affecting flow rate is pressure. With a full tank of fuel sitting above carbs, there is significantly more static pressure from fuel weight than when down to the last dregs in the tank. So if you're going to see fuel starvation issues it's most likely at lowest fuel levels, assuming bike motion, lean angle are ignored.
 
Also, I can't recall ever having fuel starvation problems when running my Commando at high speed with one 1/4" line tap open.

I obviously wasn't riding fast enough. :)
 
L.A.B. said:
The spare 1/4" banjos I have are larger than 1/8" and closer to 5/32" (0.156").
Click to expand...
Using your .1 and .156.: the combined area of the two carb float needle jets is .016 sq in. The area of the banjo is .019 sq in. Not a fluid dynamics expert, but that seems slim.
 
L.A.B. said:
Also, I can't recall ever having fuel starvation problems when running my Commando at high speed with one 1/4" line tap open.

I obviously wasn't riding fast enough. :)
Click to expand...
I run see through fuel filters about halfway between petcocks and carbs. They typically show an air gap above the steady state fuel level within. Not sure why that air pocket appears and why sometimes it disappears with filters showing full of fuel. But a few times when air gap is there, if I blip throttle I will see the fuel level within dramatically drop with each blip of throttle. It quickly recovers. Just an interesting observation.
 
marshg246 said:
Using your .1 and .156.: the combined area of the two carb float needle jets is .016 sq in. The area of the banjo is .019 sq in. Not a fluid dynamics expert, but that seems slim.
Click to expand...

However, without knowing the rate of fuel consumption at "high speed" and therefore the actual flow rate required to keep the float bowls filled then it's a moot point.
Also, it's working on the assumption that the float valves will be continually fully open which is unlikely to be the case in my opinion as the floats/float valves must continue to maintain the fuel level in the float bowls even at high speed so the float valves must still be limiting the quantity of fuel entering the float bowls to some degree or the engine would rapidly starve if demand was greater than the fuel could enter the float bowls which don't think is the case or at least I haven't known it to happen. As I said, perhaps it's just that I don't ride my Commando fast enough if I ever did.
 
You must log in or register to reply here.
Back
Top