Fuel pressure over-riding seats?

[oldcarnut]

I have a fuel issue I need some help with.  70 RR, 383, new mech. fuel pump, 5/16" lines, rebuilt carbs.   I changed my fuel pump as the last thing to do before I started trying to take this car for a ride.  Didn't have no problems at first but then the RR started flooding while driving and leaving me stranded until it decided it had sat long enough.  Initially it would crank up fine but as I got further down the road it started running rough and then shut off.  Points., condenser, plugs, wires, and cap have all been replaced.  After looking down the throat of the 3310 Holley I had on it I could see fuel was dripping out the primary air horns (engine off) until I turned the bowl level check screws to release excess gas.  Reset the floats and drove only to have it do it again several times.  This carb. ran fine on my 440 when it was on it.  I then rebuilt the original AVS and it's still doing the same thing only it hasn't left the driveway yet.  I checked the fuel press with a gauge plugged into the line by turning it over a few times and pressure bumped up to about 5 1/2 - 6. It held the pressure until I vented the gauge and then it went back to zero. I don't feel like the carb levels are set wrong and its all new stuff inside.  Could it be that I'm getting too much pressure to over ride the float seats when it starts running?  I also keep reading about return lines but I don't see one on my car.  I have one going tank to pump and pump to carb.  There are 2 more lines out the tank-both of which look to be vents (one runs though trunk and back down into ? (couldn't see the end).  Don't see anything to indicate one was ever there.  Any suggestions?  I'm ready to get back to starting my project. Thanks, David

[oldcarnut]

I cranked up the engine with the fuel line connected to the gauge.  While just running off of what was left in the carb., idle was better and pressure was 6.5 -7.  Doesn't leak down afte shutting off.  How much pressure is too much?   I think I'm going to try another pump unless someone comes up with something else.

[acelondon]

Your pressure should be ok, and we need some of the old timers to chime in with their wisdom, but i think you need a return line.
My 74 Charger has a charcoal chamber and also a return line.

[ryan053]

could it be vapor locking? How are the fuel lines routed?

[b5blue]

The extra line your thinking of is a vapor separator, it mounts between the pump and carb and the small line runs back to the fitting on the fuel sending unit (into the tank).Try a Carter M4845 (rock auto has them for 35.00) this is a factory replacement pump and if you have steel lines from pump to carb you may need a brass adapter to connect it to the pumps outlet, that's how the factory did it. (I found this out from Maxwellwedge) This pump runs 5-6 pounds pressure and has lots of flow. Your pressure sounds right though...depending on your set-up and lines you may be getting vapor lock (the fuel heating up and boiling, forcing it into the carb (?) is the heat blocked off on your intake? If it's aluminum it should be (with a 1/8 hole drilled in it to let some "heat to the choke pull off"). I had a heat soak problem (hard to start when fully warmed up) and that seems to have cleared it up. You have set the "wet level" on the bowls right? Hope this helps if you do a search on the separator you can see all about it, I retro fit mine in by running a new 3/8 line to the pump and used the old line as a return to the tank. With that and the "heat" blocked off as per mine fires right up now. 

[oldcarnut]

Thanks for the input guys  .  What I have is one steel line from the tank to almost the pump.  It's attached by a rubber line.  From the pump to the carb. is a rubber line that has an inline filter to a steel line.  It runs from the pump to under the front of the engine up under the alternator to the steel line coming out of the carb.  The tank has only 3 lines.  One to pump, 2 for vents.  I don't see any evidence of any brackets, mounts, or cut lines for another line that would have been a return from the pump.  I shot a pic of the pump and tank.  The last time, I didn't have it running long enough to get warm for vapor lock.  The intake is stock and as far as I know it hasn't been off but I didn't know that the timing gears had been changed either until I cleaned out the broken plastic in the oil screen (another story).  The float drops and lifts were set to the specs on the rebuild sheet.  I saw a pic on the separators before I posted and thats the first time I've seen one.   If I ran a return line I'd have to cut one of the vent lines on the tank .   Wish I knew more of the history on this RR but I'm just trying to get it drivable so I can work on it and drive it as I go.  It will fire right right up.  Even tried to start with the carb. off and turning it over to check the pressure the first time.  Must have had some raw gas still in the intake/cyl. from the previous flooding.

[ryan053]

Is the gas fresh? If the carb ran fine on a different engine im not sure i would suspect the carb being the problem on this engine. Whats the history of this engine? has it been sitting along time? did it run properly with a different carb before?

[maxwellwedge]

If it is an original 383 car it did not get a vapor sep. or a return line from the pump to the tank. That was a 440/Hemi thing. I see in your first post you mention "carbs" and 3310.....either way you have one or more Holleys so we can go from there.
The pressure looks fine so the culprit is a stuck needle and seat(s) defective or from dirt, wrong float level, bad float or wrong length needle and seat.

Try pulling out the sight plugs while the engine is idlng - does gas fly out of the hole? If it does, lower the float level. If that doesnt work, pull out the needle and seat and check for dirt in it. Are the floats ok? A leaky float will take on gas and hold the needle open.

I think the sending unit should only have the one outlet for the fuel line unless the car was built for California. Do you have an N95 or N97 on the tag or build sheet?

[oldcarnut]

The pressure looks fine so the culprit is a stuck needle and seat(s) defective or from dirt, wrong float level, bad float or wrong length needle and seat.

Try pulling out the sight plugs while the engine is idling - does gas fly out of the hole? If it does, lower the float level. If that doesn't work, pull out the needle and seat and check for dirt in it. Are the floats ok? A leaky float will take on gas and hold the needle open.
I had done that to the Holley that I first put on it but it all looked ok.

I think the sending unit should only have the one outlet for the fuel line unless the car was built for California. Do you have an N95 or N97 on the tag or build sheet?
It only has one.

I went back into the Carter AVS that I had just rebuilt to recheck things.  Float levels were ok but I didn't really like the way the tangs holding the pin on one float were so I swapped it out with another just to eliminate any possibility.  I also found one of the metering rods had got a little bent in the process so I changed it out too.  I connected to top half to the fuel line and turned it upside down to check the float shut offs while cranking it.  Seemed to hold decent.  Gave it all another good cleaning and put it all back together.  One of the things I did must have fixed it as its running good for now.  Took the car out on the highway for the first time and mashed the pedal and ran it up. All went well and even the smoking is about gone.  When I bought this car the owner said the engine was shot, no oil pressure. and wouldn't run.  So far with some good fortune none of that has shown up as it was all due to minor things wrong to be corrected.  I reset the timing too as it was off the chart.  Still needs a little adjustment to get rid of the backfire on flooring it from a low rpm.   Thanks for all the help guys.  At least I can drive it some and not get left sitting for a while.  Got one brakebooster issue to work out and then to checking electrical circuts.  It's been at least 15 yrs since this RR ran the roads as far as I know.  Texas tags expired in 94. 

[ryan053]

Thats good to hear

[b5blue]

Great news!I would be sure to clean the fuel system out...it's a pain but good to know how the tank is doing and if the pick up's filter is still OK. A friend got a very good deal on a six pack car years ago just because the oil sender went bad. It showed 3lb of pressure and the guy thought the block was shot! Good Luck with it!

[maxwellwedge]

Go hunt some Chebbies!