Well that's getting into carb design, and altering the dynamics beyond the manufactures multi million dollar R&D. The orifice of the seat is far smaller than the ID of the line. So if that same orifice is fed with a 5/16 line, a 3/8 line or a 1/2" line or a 4" pipe it doesn't matter. At 4 psi that orifice will deliver the same flow into the fuel bowl no matter the volume behind it. More flow volume at 5psi and less flow volume at 3 psi. Where it makes any difference at all is if the engine sucks the fuel out of the bowl faster than the orifice can fill it. Then you're going to need either more psi or a bigger seat orifice. Too much psi can override the seat valve and flood the carb and too big of an orifice can allow too much fuel to pass and flood the carb. Maintaining The float level and having a consistent level of fuel throughout the operating range has a great deal to with how much fuel the jets deliver. A float level too high by the designers ideals is going to deliver more fuel than it will at the proper float bowl level. This might cause the casual tuner to go down a jet size. On the other end, a float level too low or an engine consuming more fuel than the orifice can deliver will deliver less fuel causing a lean condition. That would cause the casual tuner to go up a jet size to correct the lean condition. In those cases the problem is fuel bowl problems cased by pressure or volume being off. In either case the jet change was the wrong way to correct the problem.
My .02 on the fuel pressure. I have run a bunch of different Edelbrock carbs, and have found that some are sensitive to more than 4 P.S.I., and some that don't seem to care. I've also had fuel pumps, regardless of what they are supposed to put out, vary in pressure up to 13 P.S.I. for a stock Chevy mechanical pump. My experience has taught me to check the pressure and keep the pressure on the low end of the spec. No more than 4.5 P.S.I. for mine.
I just want to throw out, I agree with both you guys. Fountains of knowledge of you will. My issue with running low fuel psi is. There has got to be a concern for piston swell. cylinder wear (Same as running to cool of thermostat) detonation and a whole host of issue's caused by a lean condition. I had this happen one time, half track, I shut it down. fuel psi dropped to 5. I am glad I did. But in an engine I bought if a vehicle, not so lucky..... 2 cylinders wiped. Its hard to imagine this much variance on fuel in edlebrock carbs. Ya mine was runnin rich. I tore it down, went through it, adjusted floats, found crap in tight passages. Leaned the jets and rods slightly. and no issue even at over 6 psi..... This gentlemen clearly found slime, and has 1/2 tank of E10. I wish him luck, kinda like burnin through that first tank of fuel in the boat stored all winter....
I don't think so. I'm running a 331 Ford with two 1406's and it has never been starved for fuel, even on the top end. I found that my plugs burn so much cleaner with 4 pounds than more than that. My kid is running a 455 Olds with two 1406's too with 3.5 pounds and it seems to like it there best. Don
BTW, just did a quick look at what HP levels with the stock Edelbrock needle and seats require as far as PSI. There is a larger needle (.110 vs .0935) available. Figures represent two needle valves flow rate.
Update,sort of... I tore the carb off today and it's full of crap again after very little running, and only a small amount of sitting.The third pic is the stuff I brushed out of the float chambers Has me stumped as it has new fuel lines,tank is clean(I opened the top and it looks like a brand new tank inside....clean steel),new fuel pump,new filter, and cleaned out the carb several times. I just installed a phenolic carb spacer, and thermo insulation wrap around the fuel lines where they pass by the header on inside of frame rails I will clean it again,blow it out,and try it again. I'm wondering if the Edlebrocks are more prone to this cause of small float chambers or type of metal?? May have to try a Holley if so
Worth noting that some rebuild kits include the largest orifice needle and seat used in that series of carb. The larger the orifice, the less tolerance for fuel pressure. (Pressure x area = force) The float provides a fixed amount of closing force on the needle, and replacing the .0935" seat with the .110" seat means the float has to provide quite a bit more pressure to close it. I had a similar problem on a Rochester 2G, someone used a kit that had the .108" seat while the carb was designed for a .083". There's nearly a 50% difference in the closing force required.
I suspect this is the problem....maybe evaporation causes the junk between uses and leaves the residue in the carb. I'm going to clean it and put fresh fuel in the tank although the fuel is only about 2 weeks old and a clean system. Are Holleys less prone to this buildup of crap?
Doesn't mean the fuel was clean, I've gotten plenty of trash from usually good sources. There doesn't seem to be real good quality control on fuel quality these days.
Well an update, I insulated the fuel line where it runs along inside the frame near the header and used a phenolic carb spacer to reduce the heat of the fuel and hopefully not boil it off when the engine is shut down. I'm still running 6 1/2 PSI fuel pressure at the carb After cleaning the carb out and finally getting to drive it a few times locally (damn rain) it seems to be doing well. I think in future builds I'll use steel fuel lines instead of aluminum, and maybe run the line under the frame....hate to do that though as I loose a point to jack the car from. I also noticed the wiring loom cover on the drivers side frame rail was starting to melt also,so I covered that with insulation too. I don't like the look of the thermo stuff, but it seems to work,and you have to really look at a tough angle to see it
Went for an hour drive each way today. (as well as some short hops locally) Looks like the carb spacer,and the heat shielding worked as no problems....of course driving it more often doesn't hurt!!!!
Here's my scenario, I run a pair of Carters with fuel supplied by a stock mechanical pump (no regulator), it works great ! Same intake and carbs on another engine with electric pump and regulated at 7psi, the engine would not start without cracking the throttle half way open. I lowered that pressure down to 5 psi and now it starts just fine without cracking the throttle. Just my experience with it.
The Jalopy Journal
