Dies when Secondaries Open (Fuel Shortage?)

[RhapidFyre]

I'm back again! I got some videos below showcasing what's happening. We have replaced ALL of the fuel supply except the gas tank itself. New fuel sender, new hardline, new mechanical pump, new carburetor.

The problem is that I got an Edelbrock 750cfm for a 350 small block, but what I'm reading online doesn't indicate our problem is being caused by being over carb'd.

Originally, before we replaced the hard fuel line, we could rev the truck up and take it out on the street. It would have insane take off, burning the tires, but as soon as it ran up through the first gear, we would lose it and have to limp it back to the driveway, because any tap of the gas pedal resulted in the vehicle dying.

Now, it's doing it just being revved up high. My father-in-law is a mechanic, helping me with this truck, and he's even out of ideas at this point. My uncle, Jim, recommended getting smaller jets for the Edelbrock before I dump money on a 600 cfm. We are doing that next.

Here are the videos showcasing what our problem is.

Overview: https://www.youtube.com/watch?v=6ntk1YdL8W0
Up close: https://www.youtube.com/watch?v=YwuNXMgy8eU

[EDIT] -
HEI Distributor
New Spark Plugs, 0.35 gap
Tried going straight into a fuel can, didn't change anything.

[Steeveedee]

Smaller jets will not solve the problem if it is starving for fuel, and as far as a big carburetor goes, vacuum secondaries are going to open only as far as the engine can demand.

To isolate fuel as an issue, drip it from a can with a small nozzle (to keep a spill from potentially causing a fire) and see if you can get some increase in engine speed that way when you open the throttle. If that doesn't help, you know it isn't in the fuel system.

[Boog]

What do the spark plugs look like? Still have the points style distributor or HEI? Vacuum advance hooked up, and working? Did this problem just happen or did it come with the truck?

[geezer#99]

You might not be under fueled, you might be over fueled.
At higher revs your fuel pressure could increase and start flooding.
Eddy carbs don’t like more than 5 psi.

What intake? Is it a spreadbore or squarebore? Could be a big vacuum leak too.

[68 P.O.S.]

Edelbrock's are finicky with fuel pressure. They recommend a regulator set to 5.5.

[RhapidFyre]

Sorry, I forgot to add - We tried a fuel regulator, it made no difference. Squarebore. Brand new spark plugs, HEI distributor.

The truck came not functioning, because the fuel had gel-ified in the lines and the old carb. We replaced the entire fuel supply and got a new carb, albeit one with too high cfm.

[geezer#99]

What pressure did you try?

Too high cfm! Never!
I ran an 800 holley dp on a bonestock 350 once. It gave me more power and mpg than the 625 afb or Holley 465 vac sec I tried.

[garyd1961]

I'm running a Holley 770 on a stock 350 now without any problems.

[RhapidFyre]

I tried the highest, at 5, then 4, and then even put it to 1 which basically never worked. It's undoubtedly getting fuel, so I don't understand how it would be a fuel shortage. The sender's filter is still clear and intact, and the fuel lines are completely new. We got a mechanic fuel pump from O'Reilly's, I guess that could be the issue.

[Rich69shortfleet]

Get a well rebuilt Quadrajet and call it a day. The problem with the Edelbrock carb isn't that it is the wrong size, it is that it is an Edelbrock carb.

[geezer#99]

Originally Posted by RhapidFyre

I tried the highest, at 5, then 4, and then even put it to 1 which basically never worked. It's undoubtedly getting fuel, so I don't understand how it would be a fuel shortage. The sender's filter is still clear and intact, and the fuel lines are completely new. We got a mechanic fuel pump from O'Reilly's, I guess that could be the issue.

Check fuel pressure. Tee a gauge into the fuel line.
Look in the carb while you’re testing it. Shouldn’t see any raw fuel just steady revving it.
Is your secondary air door free to move. I’ve seen them get stuck before.

[68 P.O.S.]

Since it's a new carb, did you verify correct float levels, vacuum connections and all of that jazz? The O'Reilly's fuel pump could be a bad unit, it happens sometimes. It will likely put out too much pressure still so the regulator will be needed. With HEI, your spark plug gap needs to be opened up to 0.045. I agree with geezer, double check your fuel pressure while you're running it and see what it looks like when its cutting out on you. And make sure the secondaries aren't stuck and move freely. Edelbrock's are stupid simple to play with so it won't be difficult to check. When you finally get it running well, looks like you need a heat insulating gasket too. Edelbrock's like to percolate fuel when it gets hot, causing hard starting.

[RhapidFyre]

Hey all. Sorry for the LOOONG wait but it has been hell going back to school and taking care of the kids and such. I finally got to do a little work on the gmc

We put a fuel pressure gauge on it right at the carburetor and we were getting a solid 9 PSI. We put the regulator on it and put it to 3.5, and we are holding a out 4 PSI now going to the eddy.

It sounds much healthier and it actually will sustain a little bit better, but still can't operate under load or will playing with the throttle. Too much too fast and "He's dead, Jim". If we play with the throttle and let it ease up to high idle we can open the secondaries and let it roar.

My father in laws next step for us is to remove the carb and check the float/jets.

[EDIT: in response]

The secondaries open, and the parts all move properly. We will be able to get a better lock at it when we can open it up.

[geezer#99]

Now that you got a handle on the fuel it’s time to optimize your timing.
What’s your initial timing and at what rpm do you check it at?

[Mike C]

Originally Posted by geezer#99

Now that you got a handle on the fuel it’s time to optimize your timing.
What’s your initial timing and at what rpm do you check it at?

This. There is an old hot rodders adage that says "90 % of carb problems are ignition". Since you know you are getting enough fuel and you now have pressure in the right range, it's time to sort out your ignition curve.

[RhapidFyre]

Originally Posted by geezer#99

Now that you got a handle on the fuel it’s time to optimize your timing.
What’s your initial timing and at what rpm do you check it at?

I have no way to check the RPM right now, but the timing without vacuum advance is about 12-16 BTDC.

[geezer#99]

Turn your idle down to the bare minimum then check your timing.

[HO455]

I fought a similar issue on my mom's GTO years ago. It ended up being a bad fuel hose. It had a fuel filter installed just before the carb with two short pieces of hose. The one closest to the carb had an internal flaw that had formed a flapper inside. The car ran fine until you got on it. Then at the top of first or midway through second gear it would just fall on its face and die. After a couple of minutes it would fire up and run fine. After checking all the usual suspects. I took it out and got it to shutdown. I coasted off the road and pulled the carb top and found the float bowl dry. A quick inspection showed the float, needle and seat all looked fine. While I was standing there with the engine shutoff scratching my head fuel started flowing into the bowl and I could hear the sound of liquid spraying come from the filter. I loosened the clamp on the filter and fuel sprayed out. After inspecting the hose I could see it was partially blocked. Replaced that 2" piece of hose and all was as it should be. The flapper inside the hose allowed enough fuel to run the engine until the fuel pump began pumping more as the RPMs increased then volume or flow rate or both shut the flapper blocking the fuel to the carb. Once the pump quit pumping it took a minute or two for the pressure holding the flapper closed to bleed off and open the flapper.

I would take your truck and get on it and when it falls on its face shut it off and coast off the road so you can pull the top off the carb see if the float bowl is empty. That way you will know if it is a fuel problem or something else.

If the carb checks out put a timing light on it and watch the flashes while you rev it up to see if you lose spark.

[68Gold/white]

Originally Posted by Rich69shortfleet

Get a well rebuilt Quadrajet and call it a day. The problem with the Edelbrock carb isn't that it is the wrong size, it is that it is an Edelbrock carb.

THANK YOU for that post, finally someone telling the truth, here!!!

OK, 750 cfm is NOT your problem. Millions of Chevy 350 came with 750 cfm Quadrajet's (yes, I prefer Qudrajets, also...)

Your float level could be too low, among many things. Your carb is likely the AFB clone. It has a weighted arm that opens the secondaries at the same rate, REGARDLESS of the size of the engine.

Revving up the engine in the driveway cannot be compared to driving it, completely different deal...

Knowing some of the facts you've been questioned about in all of the post's before mine will help understand what's going on!!!

[RhapidFyre]

Responses -

Steeveedee
Tried direct starter fluid and fuel, no change. Same behavior.

Boog
Spark plugs new gapped 0.35 (need to change to 0.45)
HEI Distributor, vacuum advance and hooked up
Hard to say if it just happened or came with the truck. We had a huge fuel delivery issue because it sat for 20 years with gas in it, that ended up gel-ifying and then hardening. So, we replaed the entire fuel supply system minus the tank itself (new fuel sender though). What I can say, is that we had NO problems with the idle when we put the brand new eddy in it, we just had performance issues with driving it through gears and on the road. The harder we drove it, the more it chugs and died until it had to sit or be limped back to the house. What changed the game, was when we put the regular on it. Once we put the regulator on it, it can't even be revved at idle without dying - Even after REMOVING the regulator! It can only drive now under idle power. Applying any throttle kills it. [Edit] Now that I think about it, adding the regulator was the first time we adjusted the timing, too. It was set to almost 0 BTDC so we adjusted it to 12, then 8, then back to 0, then back to 12, and it doesn't change much.

Geezer#99 / 68 P.O.S.
Regular is on and set to 2.5, getting a constant PSI of 4, even when it dies out.


68 P.O.S
We didn't verify float levels, but all connections are set. I took the carb out of the box and threw it on the 350. I'm just now learning that carbs may not always be plug and play out of the box, but not sure what to set/change.


The reason I'm comparing revving and driving under load is because it's behaving quite differently to each, but in a similar fashion. Revving it at idle kills it as if it was starving for fuel, but we now know with the fuel pressure gauge that it's not the case (at least, up to the carburetor). I used to be able to drive it but it won't even move now (refer to the reply above to Boog), unless it's under idle power only.

When we first threw the eddy on it, we could take off initially out of the driveway and burn rubber, scream through first gear, and start climbing second. The approach to 55 MPH is when it started to fall off, and once we started to fall off it was totally down hill. No more acceleration, you COULD maintain your speed if you were easy on it, but then the falloff started and it was downhill from there. Once it died-died, you had to let it sit for a while or limp it back. Now, you can't even drive it.

[68Gold/white]

Make sure your carb base gasket covers up all the openings in the intake and the carb.

Sounds like you have a vacuum leak...that may have just got worse...

[Chris_oz]

It is starving for fuel, plain and simple.

You have replaced the entire fuel system other than the tank, how did you clean out the tank? are you sure you have a steady solid fuel supply to the pump?

Have you tried it with a separate gas can, clean, fresh fuel line from the can straight to the pump to ensure the pump has a steady supply?

When it dies on the road, is the fuel filter full or empty?

It takes next to no fuel to allow an engine to idle and even rev with no load if you go slow and creep it up.

You said you could "race through first gear and into second" then it dies. About enough time for the fuel bowl to empty.
You then say it needs to sit. is that sitting at idle? or engine off? I imagine at idle, allowing the fuel bowls to get some fuel back in them.

Do you have a filter before or after the fuel pump?
Filter after the regulator?
You need the regulator, at 9psi an eddy will flood all day long if the floats are not stuck or inlet blocked.

Confirm you have fuel flow from the regulator, put a long bit of hose from the reg into a container and crank the engine, you should have good steady fuel flow with each crank.

CHECK the float level and ensure that the floats are moving and free, I have had more than one jammed down, causing huge flooding, but have also had one stuck up causing a dry bowl.

The fact you could drive it a little with 9 psi fuel and not with 4 psi tells me the fuel is not getting into the bowls as it should, they need 4 to 5 psi and no more.

It does not sound like its running long enough to be getting a vacuum in the fuel tanks, causing low fuel pressure under load, but check anyway.

Set your base timing at 8 deg with vacuum disconnected and plugged at carb at 600 rpm in neutral, hook up the vacuum and make sure you have a max of 32-34 deg advance at 2500 rpm (all in) this will get you close enough to sort the fuel issue.

I have only had one new carb out of the box go on and run as it should,
(A street demon 625 cfm) without a flooding or starvation issue, being bounced around in a couriers truck is not what they like.

Check fuel flow to the carb, confirm it into a bucket.

Check the float levels.
Put a bit of fuel tube onto the inlet, with the top of the carb off and the floats hanging, like you are checking float drop, blow with you mouth into the hose, ensure that both needles let air through easy, no obstructions are in the passage.
If you have compressed air, remove the floats and needles, blow backward through the seats and ensure it comes out the inlet without restriction, I had a chunk of rubber stuck in an inlet once, very annoying.

Refit the carb, hook it all up, make sure all PVC and vacuum outlets are plugged if you are not using them, crank it over, within a few winds the bowls should be full and the accelerator pump should give you a nice squirt down the throat.

Fire it up and set base timing, then run it up to 2500-2600 rpm and ensure all in timing of 32-34 deg total advance.

Now go for a drive.

[jeffahart]

Here's a post I did you might want to read. You just have to keep at it. I've never really had any problems with a Q-jet or a Holley or a Weber or Mikuni or blah blah blah but sometimes electronic ignitions can give me a headache! Go borrow a carb off someones truck and plug it in. Shortest path for you in eliminating that carb as the problem. At some point you have to call it and bust a move.

http://67-72chevytrucks.com/vboard/s...d.php?t=742187


Keep at it, good luck!


j

[RhapidFyre]

Originally Posted by jeffahart

Here's a post I did you might want to read.

Hey Jeffahart - Thank you for the post reference. Interesting case, with the spark from your vibration simulation. I'll definitely check it out for kicks, but since this is happening on level concrete ground with no vibration, I think it's going to be unrelated. This problem (not under load) never started until we screwed with a regulator and the timing.

Originally Posted by Chris_oz

It is starving for fuel, plain and simple.

Hey Chris! As previously stated, I set up a fuel pressure gauge right up to the carburetor and it's getting sufficient fuel even while it's about to die out. Definitely no issue with the fuel supply.

I am definitely going to heed the advice of checking the float, and redoing the timing. Thank you for that in depth information
'


We're taking the carburetor off this weekend/early next week, and we're going to check the float and the jets.

[jeffahart]

Originally Posted by RhapidFyre

Hey Jeffahart - Thank you for the post reference. Interesting case, with the spark from your vibration simulation. I'll definitely check it out for kicks, but since this is happening on level concrete ground with no vibration, I think it's going to be unrelated. This problem (not under load) never started until we screwed with a regulator and the timing.



Hey Chris! As previously stated, I set up a fuel pressure gauge right up to the carburetor and it's getting sufficient fuel even while it's about to die out. Definitely no issue with the fuel supply.

I am definitely going to heed the advice of checking the float, and redoing the timing. Thank you for that in depth information
'


We're taking the carburetor off this weekend/early next week, and we're going to check the float and the jets.

I would swap the carb, borrow one from someone that works. You need to rule out the carb. You will question your work on the carb, and your carb fuel bias will pin you in a hole for hours of work.

Just remember "never started until we screwed with a regulator and the timing" and this creates the bias that can cause you to spend hours even days.

In my write up my bias was vacuum. But I knew better and even if someone would have told me spark, and maybe someone did. I didn't listen because I personally checked it myself.

Not saying your problem isn't fuel. Just saying, when you find the problem you may be getting a good laugh.

Path of least resistance, a test carb that works. Have these mechanics dig one up an put it on. Then when you know your carb is bad, you can play with it and rebuild it and gain some experience with that. Fun!

Poor carb... he get's blamed for everything!


J