Fuel Mixture Control

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Daniel,

Except that there isn't really any choice when integrating the needle into the carb. For those who believe they need the fuel line between the needle and the carb to be as short as possible, they settle for a less than ideal flow direction in exchange.

Thanks. Brad.
Titan Racing Components
BlackJack Hydros
Model Machine and Precision LLC
 
On March 21, 2020 Bob Violett passed away! He sold BVM models 3 years ago so the true answer to the setup of his 3rd needle may not be available. To my knowledge Stu has not changed the original design so if you choose to follow the recommended fuel flow you should achieve optimal performance.
An explanation of Bob's design may simply be about pressure. If you flow against the needle the pressure should be greater and more consistent than with the taper of the needle. Bob was an airplane guy and he new all about airplane engines and planes flying inverted and vertical. You need good fuel pressure to keep your engine consistent.
 
Last edited:
Great input to my simple question I raised after reading the directions on a new Bob Violet mixture control, FOR THE FIRST TIME, after using them for years.

The bottom line there is really not an absolute answer.
 
I talked with Bob many years ago when I started using his valves. I don't remember his reason for a flow reverse from other valves. The flow meter shows a different # when you flow with the taper. I have always plumbed as Bob suggested. Have not had one of these valves fail me. As with all valves, you need to replace the orings in them because they do wear. Once a year is always a good practice.

I was somewhat forced into doing production of this valve. Otherwise, this product would have gone away. My performance with many other valves has been as good as with Bob's.

I use the same suppliers that Bob uses on all the metal parts. Injection molding is done in INDY with the molds that Bob created. The flow chart on the instructions is actually a reproduction from Bob's instructions.

Stu
 
Since I get a leaner mixture flow on a Boris meter going against the needle, that tells me it’s harder for the fuel to go that way. You could call this a restriction. I know you can open up the needle, just sayin’. I like filling the cavity first , towards the needle on our boat application.
 
James
The best way to find out is to pull the shaft out and see which opening is bigger.

Dave
 
Weird, it's just as you guys say.

I checked the old Carl Brey needle for my dyno and flowed it at 10.0 (old school) down the needle. Flipped iy around and it only flowed 9 or so into the point.

Question is why?

I guess an orifice isn't just an orifice. :confused:
 
Terry
It's because your trying to died head it on the small in the the needdle .hydraulic part of the pressure goes up and that isn't the way to flow pressure.Read about hydraulic pressure.
 

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