Overlooking something? Fuel Starvation

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GoodysGotaCuda

Mr. Goody
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I have had a 650cfm Thunder AVS on my 318 for about three years now.

Its a slightly worked over 318, 3500stall, 3.91s, it currently runs mid 13s, when it was jetted too lean. The issue I am having right now is one bowl on the carb is getting sucked dry on heavy throttle, even sometimes rolling into the throttle slowly . Engine falls flat on its face.

I have:
New fuel system, 3/8" Lines, sender to regulator. Holley blue pump, set at 6psi, tried it at 7psi..No change in problem.
I have setup a dual feed for the carb, both -6an fittings
I have high flow needle & seats. 110" if i remember right
I have 'Pink' Metering rod springs
I am running .075x.037 metering rods with .107" primary, and .119" secondary jets. (rich, very. biggest secondary jet availible)
I have checked, and rechecked float level

*I am wondering if too light of a metering rod spring could cause this?
*Am I out running this carb for fuel with the jetting i have in it? It holds a good air/fuel ratio with the current setup, I just can't get it to run straight and am wondering if I am out-flowing the carb?
*Is there a possibility that a needle can be sticking in the seat with 6/7psi of fuel pressure against it?

Thanks! I feel like im overlooking something stupid....but dang, this ones gotten me good!
-Mike
 
Mike, What Changed? anything little, big?
Do you have a fuel pressure gauge? if so where is it getting its feed from?
What does the gauge do when the carb is dry, if there is a restriction somewhere it will still show 6-7 PSI but not moving much fuel. Also how long does it take to fill the carb backup up and run ok?
 
Had a problem like that once. Everything was OK until I changed to a steeper rear gear (3.23 to 3.91). Swapped the 650 Holley for a 750 and the problem went away. For some reason 318's like to be over carbed, at least when they have vacuum secondaries. Never tried a double pumper that size so I can't say how it would work.
 
Not sure what's up with your carb, but I ditched my Edelbrock carb long ago because no matter what I did, it had a flat spot and had no top end. It would idle all day long, but after I got wasted by a 5.0 Mustang getting on the freeway, I swapped it for a Holley 650 DP and never looked back. With the Holley, it's a whole different car. I picked up 4 mph in the 1/4 with no other changes.

Edelbrock makes great manifolds, but their carbs SUCK for performance. They're great for cruisers and street rods, but if you're looking for max performance, you're fighting an uphill battle and leaving HP on the table.

JMNSHO.
 
Fuel pressure gauge is on the carb side of the regulator of course. its an autometer liquid filled, visible from the drivers seat. It takes a good second or two of no throttle for it to pick back up and driveable. I've changed out the fuel filter (big canister filter), lines i cant see why there would be a restriction they were replaced about 2 years ago. Carb pre-filter is clear, needle & seat screens are clear. Im wondering if for some reason my needle/seat is sticking, or i have a faulty float...somehow.

My current issue with holley is i've had two. Used ones. For the LIFE of me i cant ever get it to run straight. Let alone NOT leak fuel all over my intake. If i were to get one, it'd have to be brand spankin new. And i don't have the $300 to get me one at the moment. I have a 3310 750 in my garage i refuse to put back on the fourth time because its now sealed...but the damn accellerator pump does not work. All passages are squeaky clean, good gaskets, etc. Nothing. If i get one, it'll be a virgin new holley.
 
I assume you have had the sender unit out of the tank and made sure it doesn't have a restriction or crack in the fuel pickup. Just a thought.
 
Thinkin i've been playing with the wrong float spec.

My book claims 7/16" needle/seat closed setting is what it should be. So thats what i've been checking it too.

So for kicks, without the engine running, i ran the fuel pump for a few seconds. Pulled the lid off the carb and saw where the level was. Looks 'too low' in my opinion. With much larger than stock jets, smaller metering rods, tweaked accell pump and larger accel pump nozzles. I might be able to take that amount of fuel out in a hurry.

So i went from 7/16s 'spec', to 5/16". We'll see what that does for me
 
I think that you are looking at the problem right now. Sound like the float is set too low. And as you said, it is getting sucked dry too quickly.

My thinking is that you need to get more fuel into the bowls and be able to keep it there for "on demand" throttle use.
 
You did the right thing by setting the floats to 5/16". I saw in the book where it says it should be 7/16 but I had 2 I couldn't get to run right set that way. 5/16 worked much better. You mentioned your running the big canister filter. Is that the one Summit sells that takes either a 2.44" or 3.25" inch Fram canister filter and is rated at 90 gph? I ask because Don on FBO has a book out for tuning and he don't think much of it. He says they don't flow enough for a performance application. You might try one of Summit's billet inline filters. They flow 130 gph. Also checking the pickup like mentioned above is a good idea. I saw one that was plugged up once causing this problem.
 
You might be onto something with the float level. Edelbrock and Carter carbs are very sensitive to float level.
 
edel brock carbs are just a name plate on an older carb,, "carter " afb or avs,, they work fine when tuned properly,, tons of guys use them on blower motors,, mopar used them from the factory,, if you cant figure it out ,take it to a carb shop,,,not tthe corner pep boys either,, edle brock suplys a book to tune your carb with, i ahve found it very help full,, very true hollys out of the box make more HP,,, but if you already have a nice edelbrock, use it,,the edlebrock wil work as well once tuned properly,,
 
Get you one of these Holleys.

0-80528 750 Mechanical secondaries (Manual transmission)
0-80529 750 Vacuum secondaries (Automatic transmission)

Or you could rebuild the 3310 you have and send it to BJR Racing. He has a trick for the 3310 carb that I'm not sure of all the details but you have to buy a metering block for the secondaries and let him do the rest. He is a member of FABO. He has spoke to me about this and it sounds it will make a car run like a scalded chicken.

4150 Carb 001.jpg


4150 Carb 002.jpg


4150 Carb 004.jpg
 
I have the 650 Eddie AVS on my car and I believe I am running .104 jets in the secondary and I believe .098 jet with the stock rod in the primary. My car picks up a tremendous amount of power in the very cold weather and slows down a lot in the warm so I know its running way way too rich. I have stock type fuel pump with 5/16" lines. You may be running the very large jets to compensate for the low fuel bowl level. I never adjusted the floats in mine since I got it but I know they are both set the same side to side. I can tell you one thing my car is pretty quick with the Eddie carb on it so its definitely a good carb.

Another interesting thing is I changed my gas tank last year and cleaned out the vent tube and that made a big difference in the fuel delivery. I believe I was jetting the carb up to compensate for a restrictive vent tube and now I need to jet the carb back down. I also assume your fuel pick up filter in the tank is not clogged? Is a fuel line getting sucked closed and collapsing anywhere?
 
I would pull the fuel line off at the carb and blow back at every interval possible, it to me sounds like a huge restiction in the fuel line like it picked up a chunk of old hose or? and YES i know someone it happened to and was jumping thru hoops tyin to fix it.
 
I had a fuel starvation problem over the summer. My car completely bogged on me twice when going down the quarter mile. We replaced the fuel tank and sending unit. The tank was very dirty and the sending unit was about shot. The sock was a mess. Unfortunatley I have yet to take it to the track to see if it helped but seems like it drives a little better.
 
what is the float drop? they say its to be about 15/16ths to 1". every carb i open, its set to about 1 1/4-1 3/8". way to low. i set it at 15/16ths.
 
Have heard many times that the Eddies floats need to be adjusted out of the box.....
 
7duster4 said:
I had a fuel starvation problem over the summer. My car completely bogged on me twice when going down the quarter mile. We replaced the fuel tank and sending unit. The tank was very dirty and the sending unit was about shot. The sock was a mess. Unfortunatley I have yet to take it to the track to see if it helped but seems like it drives a little better.
Click to expand...

It wouldn't hurt for me to check everything out on my car. I never have. I got new 3/8 fuel line that should be here today so everything from the tank to the carb will be new. Now the inside of the tank is a different issue.

Most of the time don't folks take the tank to the radiator shop and have them clean it?
 
looking like chasing two problems, float level helped a lot. cap/rotor is looking pretty chewed up, so thats gonna get swapped out too.
 
OK I'm confused. You say you have a fuel pressure gauge mounted between the regulator and the carb. I'll assume you have the reg set for like 5-6 PSI in a FLOW condition (driving down highway, not at idle). So, here's my question; does the fuel pressure drop at the same time the carb is "running dry". Your second post leads me to believe that "It takes a good second or two of no throttle for it to pick back up and driveable." So what this tells me is you have a fuel delivery problem upstream of the carb. If this is the case NO AMOUNT changes made to the float levels, jets or needles will fix the underlying problem. You may be able to mask it somewhat by overfilling the float bowls, but if the pressure is dropping you are not getting the fuel into the carb when it's needed. 11/32" sticks out in my memory for AFB/AVS carbs, but check what Edelbrock says. 7/16" seems a tad low.

As suggested, I would disassemble the ENTIRE fuel delivery system from regulator to tank pickup, back-blow each segment with an air hose, and replace any piece of rubber line (especially the segment at the tank). Blow each segment into a shop towel so you can see if you blow out any crud. I would also remove the pickup from the tank clean it and take a good look inside the tank (use on of those LED powered water resistant flashlights if you're nervous about the fumes). Anything other than clean fuel must be removed.

Next I would suspect the regulator. Is it a Genuine Holley regulator? Some of the look-alikes and parts house specials aren't too great. Try adjusting the regulator to provide an additional 2 PSI to the carb. Does this change anything?

If you have steady 4-5 PSI at full throttle you either need a larger needle/seat, or the carb isn't your problem. Good luck.
 
Mike, how well is the fuel tank vented? Most are simply a small 5/16 ID rubber hose, that easily kinks over time. If it's mostly blocked, the pump may be drawing vacuum on the tank. I've had no issues, and driven for 20 miles, and then not been able to re-start the car after it "vacuum locked". Also, ditch the liquid gage. It's easier to read because it doesnt react fast at all. I agree with C130... I think you're chasing you tail... Unless it's totally fixed now...
 
thanks guys. i'm pretty sure its just down to a crappy cap & rotor and it was just a low float level as well. I have enough info through this thread to go through everything if it doesn't solve the issue. ill get to it this weekend.

thanks
-Mike
 
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