3rd Channel Needle Length Myth?

[Tom Foley]

Dale Powell is the man who made those carbs (D & J )

 

[dwilfong]

Dale Powell is the man who made those carbs (D & J )

Ya thats him Dale

He was running a RR with a Rossi .61 Aero eng in it.

Real nice guy.

Now I have some one to talk Nitro with at the pond besides Lupe.

 

[dwilfong]

I run a remote needle on my mono that has some fuel tubing length to it,when I do adj. to it happens in about a straight away. On my 21 rigger I have the 3rd channel built into the carb,as soon as I touch the needle it is right now. I think if you pulled the fuel line off your engine at the nipple of the carb it would spool up faster than if you just pinched the fuel line at the tank...No?? It works that way with my airplanes... I could be wrong.

I did some testing at the pond by accident last weekend.

I drilled out the spray bar REAL BIG on my 1.05 and it ran real good. well the spray bar hose nipple broke because I drilled it out to much. So I put the stock one on just drilled a little.

Well It ran the same till it came to the corner's. Then the eng would bog. same setup just a normal size spray bar hole.

Very interesting results.

I use the Du-bro .125 extra large hose from the needle to the carb. about 5" long.

The flow across the needle can not change that quick to adjust to the load.

The fuel LOG with a LARGE spray bar can.

The length of the line is the reserve and can be tuned to the load change and time demand of the boat.

Just some thing I have bin pondering.

A accident some times leads to a enlightenment.

 

[Joe Warren]

What is being done is no different than changing jets in a fixed jet carb similar to a dirtbike . Venturi suction is what it is dependant on the venturi size and throttle opening except our systems have a bit of pressure due to the exhaust . This is similar to a HP carb setup on a car or boat that has to assist the diaphragm lift pump to keep fuel in the float bowl under hard demand .

True but we have a variable MAIN JET, And we contuine to close it off to Make Heat & increase the piston speed & see results, Then Only by Ear do we listen to see if we are happy with the correct adjustment?? Seems a little crude?? If the thrird channel is extremely close to the carb & the engine can consume more fuel on the low pressure side of the needle than you are letting thru the needle it is possible to suck the needle & seat dry on the third channel. this is normally under loaded wet boat conditions like corners, or when you have partial throttle openings and the pipe pressure is low and the venturi is at its highest vacuum. p.s. the pipe pressure is mainly on the pressure side of the needle and seat on the third channel.