I still feel like I have a fuel supply issue... I have been running really well for the past few weeks (after the header/GT40P/Torker289 swap) but every now and then, (usually when someone is in the car and I am showing off ) , it hesitates at takeoff. I have "sorta" in a semi-quasi-scientific way, figured out that if I cruise out of the neighborhood and just slowly cruise 30 mph to the highway, then wait at the red light, then gun it onto the highway, it will immediately hesitate for 1/2 second or so, kinda sputter a little then it takes off OK, but it doesn't seem to have the power it did when I first did the swap. Yesterday, I tested it by running 2nd gear all the way to the red light, keeping the RPMs up to 2500 or so, then not stopping for so long before taking off, and there was no hesitation. I still find my fuel filter empty if I idle for too long, and cannot help but think that I am not getting enough fuel flow gphs at low RPMs. Currently running 600cfm carb with the Edelbrock 351 mechanical pump. I can fill up a gallon can at 2500 rpms in about 38 seconds. But it takes much longer at idle and lower RPMs and I am fearing that it is the idling up to the line that will kill me at the track, when it spits and sputters at takeoff. Is anyone running two electric pumps, one near the tank to push the fuel forward, and one near the engine to push it up to the carb? I am thinking that is my solution. Also, if one goes out, will the other one still be able to push through the dead one, or will it block the entire system?
You might look into either getting a Holley Mechanical replacement pump ..... or.... remove the mechanical pump (attach a block-off plate, see LINK) an electric pump (LINK) and Fuel Pressure Regulator (LINK). Food for thought. Gluck.
my glass filter is fairly empty at idle, but i have no problem going down the track. using a carter hp mechanical pump. mechanicals pull well from the tank even tho mounted in the front. electrics are pushers; not pullers. mount a helper electric in the rear by the tank if you want. only use it at thetrack, or use it all the time; your choice. i was once told long ago its not wise to use a helper electric on the street all the time. there was a fear that the electric would eventually rupture the diaphram in the mech pump & let you fill the crankcase with gas. a good mech pump with an adequate fuel line/system should supply your car well. you can put in the electric and it might band-aid the problem, but i doubt the mech is the real problem if functioning properly. if you have a holley carb, do you have the clear sight plugs in it? if not, get them and see what the float level is at idle, for starters. then check out the line back to the tank. crimped? tank pickup clogging?
It sounds like a pump shot issue to me. You may want to experiment with different squirter sizes and see if clears up the stumble. As for installing two fuel pumps, it seems like you are working to overengineer the fuel system. One fuel pump should be more than adequate for your car. I am not even sure the fuel pump is the issue. I know of nobody who runs N/A who runs more than one pump and once the car is tuned properly, all is well. Every time i have been in a car that did not have enough fuel pump, the problem exposed itself at high rpm not off the line. Since you are concerned about the output of your pump, why don't you install a fuel pressure gauge to see if the pump is functioning as it is should?
Fred, good point. I have "assumed" that the edelbrock mechanical pump is working fine, but then double-thought myself due to the filter (which is just prior to the carb) being empty or half-full that the 6psi that is required is being fulfilled. Should I install the pressure guage before the filter, or after? Or does it matter? I would like to see the filter full all the time, since it suggests to me that the fuel system is getting plenty, if not more, fuel to the carb than is needed. I would rather have more fuel available to the carb, rather than too little.
I wouldn't doubt that is trapped compressed air you are seeing in the filter (edited per DS remark below: 6-8 psi). The fuel line is still under pressure - in fact, gasoline itself (being a liquid) can't be compressed. The air in the fuel system, however, is compressible. I'm not a carb guy but I did stay at a Holiday Inn Express last night.
I would install it between the filter and the carb. If you are feeling especially industrious, you can also try it before the filter to see what, if any, difference there is.
Your Edelbrock will only function properly at the proper fuel pressure ... 6lbs or so I think ... Hesitation from a stop I would think is an accelorator pump issue or a choke issue ... When you open the throttle do you get a nice squirt of fuel down into the carb from the accelerator pump in the carb?
I am seeing a nice healthy stream of gas shooting on both sides when I push the accelerator. As for air in the system, do I need to bleed that out, or will it eventually bubble through the carb? Does the mechanical pump run the required 6 psi at idle through rev, with only the volume changing, or does the pressure increase up to 6 psi as you rev it? As for the "choke issue" this as only happened since it has cooled down. Are you suggesting that my choke may not be fully opening causing this hesitation? It is the electric choke 600cfm edelbrock, so the choke could be kicking on/off when it wants to. I guess I could pull over and pop off the air cleaner next time it does it and check to see if it is open. Then back the choke adjuster off a bit. It is a little hard to start on cold mornings, so I keep the choke pretty tight (advanced? ).
Scott, you won't need to bleed the fuel system to remove the air bubble (in order to correct your problem). It wouldn't hurt to do so, but it's not necessary (IMO). I think you might be onto something with your choke.
Make sure you choke is properly connected and you are getting 12V to the wire. A couple of weeks ago I took my Grabber to a car show ... it was about 20 degrees outside and I had never hooked up my choke. It ran like crap ... stumbling, hesitation, the works. I came home that night and hooked up the 12V and tested again the next morning. It ran fine after warming up. If the choke doesn't open it will run rich at idle and then starve for air at take-off and stumble like crazy. Unless the linkage is disconnected the choke will not open/close when it wants to. The 12V is merely heating a coil inside the housing to slowly open the choke over a short period of time ... in the old days a heat tube from the exhaust did the same thing. Just make sure the choke eventually opens or it will not run very well ...
one thing i would like to add.... you did add on a lot right... new headers.... new heads... with more flow.. this may be for off... but just throwing ideas im not sure of your whole setup... BUT... the more you "add" on the more fuel you will need. if the carb isnt getting enough fuel.. it might lean out?.. and as you hit the gas it may stumble a bit.. i am having the same kinda problem.. but not quite the same.. i re jetted mine.. and it seems to hesitate if i hammer it when i am already moving.. for instance.. if i am cruising at 35 mph.. and i want to pass someione.. i down shift to 2nd.. and hammer it it.. it "burps" then is off like a rocket.. im not sure why it does that.. but seems like its only since it got cold and after jetting...i was thinking of adding a choke cable to play with it and see if that helps.. well just my .02... good luck
