I have a friend who owns a 66 Nova drag car in another state. It doesn't perform up to what would be expected. So I told him to ship me the 850 Race Demon carb and I would take to a local friends business http://www.competitioncarburetion.com/index.htm

Well it got the $500 job with new boosters..... bench flowed, and ran on a dyno test mule engine. Now all set up for E-85 fuel. I packed it up a shipped it back. Well he puts it in his car and gas is coming out every where and he's pissed and calls me.

So with your help please correct where I'm wrong on this letter that I'm composing to send to him.

Nobody runs 9.5 PSI fuel. Well apparently you and your friends do!

Just sit back and read what I have to say You just have to think about how a needle and seat valve works. You have fuel input pressure on one side and a carb bowl float on the other. The needle and seat has a tiny spring to fight inlet pressure. So when the bowl is full the float is up and the needle valve is closed.

The higher the inlet pressure the faster the bowl can fill. But what happens is the needle actually spends more time closed fighting pressure. So it is better to have smooth continual flow with pressure never exceeding about 7.5 - 8.00 PSI for gasoline. They actually run fine at 4.5 psi. It just means that under high demand that the needle valve is open all the time to maintain a upper limit float level.

The negative effects of too much pressure: aeration of the fuel in the bowl because it is squirted in at high velocity. The needle and seats ware out do to bouncing open and closed because of the faster fill times. Did you know that stock mechanical pumps that they put on millions of vehicles on the road run a max of @4.5 - 5 psi. It was only hot rodders that decided that aftermarket pumps need to get up higher psi.

Another point is that needles and seat come in different diameters. Look at a Summit Cat. and you will find titanium, stainless, alki.... You have higher flow bigger diameter gas needle and seats They flow 50% as much fuel. Again that leads to less fuel pressure required.

Now like your Alki motors and E-85 motors require twice the fuel flow so they get even bigger needle and seats. But they just have a the same tiny spring. Because the needle is BIGGER surface area and some guy puts way too much pressure (9.5psi) on the inlet side. It actually over comes the spring and holds the needle open flooding the carb and blowing gas out of every where.


SMART people run bypass return to the tank systems so the fuel is always cold at the inlet and they run no more pressure than required. Like start at 6 and see if it has any indication of fuel starvation at the end of the ¼ mile

 

I like it, push send.

 

Many people confuse 'flow' with 'pressure'.

Ask him if it's faster to fill a swimming pool with a half inch hose at 30 psi or a 10" fire hose at 5 psi.

 

Don't tell me he's running over $500 worth of specialty carb on a race only car without a fuel regulator? It takes only seconds to change and try different fuel pressures. With electric fuel pressure gauges so cheap now there is hardly an excuse not to run electric fuel press gauge in the cockpit - mine is in the instrument panel clock hole.
A great tuning tool is an installed vacuum gauge - something overlooked. With vacuum u can monitor how your engine reacts to carb mixture and timing changes.

And this is really old school stuff,
cardo0

 

He has a electric pump, regulator, gauges.

Just a mind set of 9.5 is what all drag racer run and he couldn't figure out why a new carb was leaking so bad.

I sent it to him and was going to call later