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Old 10-19-2016, 04:55 AM
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69 el Camino stumbles at high rpm

After sitting for 5 years, I finally got my 69 el Camino back on the road. In the last year before I got it running, I installed a used, running crate 350 with a quadrajet on top of an Edelbrock performer intake. As far as I know, the cam is whatever came in the crate engine. I bolted my shorty Hedman headers on, and those go through 2 1/2" pipe into Maganaflows. Behind the 350 is a 700r4 with a non locking converter I got free from my uncle. Out back is a 9" with 3.23 open gears and disc brakes I added. Before I started the engine, I dropped the gas tank, and thoroughly cleaned it out with acetone. I rolled marbles around in it as well. After that, I power washed it inside and out at a self car wash. I then let it air dry, then painted the outside.
I only mention these things to give an idea of what I've done recently in case it might help. The car ran great for 2 months, giving me no drivability issues, until this out of no where.
My issue is that within the past week the car won't go above 3500 RPM without stumbling and almost dying. It started close to 4000, then got lower to around 3500. Last weekend I couldn't get it above 2500. It feels like it is running out of fuel. I changed brands of fuel thinking that might help, but it didn't do anything significant.
Two nights ago I pulled one of the fuel filters because it was filthy. I have the clear glass style fuel filter before and after the pump to make sure the pump is functioning properly. I took it for a test drive and nothing changed at all.
Last night I bought a harbor freight vacuum gauge and adjusted the qjet to that highest vacuum I could get. The car runs great for a few seconds, then stumbles and tries to die. I can get it to 4000 RPM once, then once it shifts, and goes back up the power band, it stumbles again. It still acts like it's running out of fuel. I can get it to idle for a few minutes, other times I can see the fuel in the filters isn't filling up the filter like it should, then the car dies. I can get it start up, but it takes cranking on it for awhile before it fires up.
Earlier tonight I checked fuel pressure with the harbor freight gauge, and I got 7 PSI. I figured the pump was still good since it was replaced only a few months ago.
I took the line off before the pre pump filter, and disconnected the line at the tank, then taped a plastic bag at the end. Then I blew the line out, and checked the bag to see if there was any debris in it. The bag only had fuel in it. It looked like fuel, nothing special. So I hooked everything back up, and now I'm at a loss.
I feel I should mention when I pulled the line to blow it out, as well as when I changed the filter, no fuel came pouring out from the tank side. I didn't have to plug it, crimp it, or put it in the air to stop it from leaking. I always thought it leaked no matter what.
The pump is the O'Reilly pump they have on the shelf in the back. It's nothing special. The pressure gauge said it's at 7 psi, even though it didn't put fuel into the line, only air. My next step is to rig up the pressure gauge while I drive, assuming I can drive it since it does stall after a few minutes of driving now, and see what I get while driving.
The plugs showed they're burning great before this fiasco, so I'm assuming that the ignition system (HEI) and timing can be ruled out. New plugs, wires, coil, module, condenser, rotor, and cap. This distributor is the one from my old 350 but it worked when parked. I figure it should be fine since everything else around it is new in the ignition system.
I've been driving without an air filter on it thinking that might help, but it hasn't changed anything at all either.
My next step is a compression check, but because it runs great for a short time, then stumbles, I don't expect any answers there.
I have yet to rebuild the carb, only because I've never done one, and small things tend to frustrate me, so I'm waiting for my uncle to help me.
Anyone have any other ideas? This is my daily, as I gave my Corolla to my girlfriend, and now we're back to one car.

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Old 10-19-2016, 06:00 AM
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Did you rebuild the carb or at least take off the top and clean if required? 7 pounds pressure is a bit high. check ignition,is the coil in the cap or external? Try to borrow one to swap in for testing
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Old 10-19-2016, 08:57 AM
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About 85% of high speed engine misfires can be traced to the ignition system.

First, Check your spark plug gap. Install a new set of the correct spark plugs, gapped at .035". If that does not solve the problem, then move on to a new cap and ignition wire.
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Old 10-19-2016, 10:46 AM
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With the history that you gave and the fact that a new carb did nothing, my first thought was a separated exhaust pipe. A lot of the exhaust used today it laminated tube. If the inside tube corrodes and breaks away from the outer tube it can collapse and cause enough restriction to limit your rpm and power.
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Old 10-19-2016, 01:36 PM
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Your clean line blow back test and the fact no fuel siphoned itself from the tank when you pulled the connecting line off makes me wonder if you have a plugged filter sock on the end of the pick-up tube in the tank.

The fact you attempted to clean the tank adds to this question, could be stuff knocked loose that didn't get flushed out or stuff now coming loose because it was disturbed. You may want to drop the tank again and look at the pick-up sock....or at least blow back through that sock and see if that temporarily helps....if it does, you'll know where you have to look.
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Old 10-19-2016, 02:31 PM
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Fuel filter was filthy?

Clean the carb, filter is a pretty coarse and won't get out fine particles.

Probably full of sludge.
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Old 10-19-2016, 05:17 PM
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sediment can come from gas stations. can be trapped in the fuel lines..

i have a few tests...

when you do the fuel pressure test and you stop cranking.. does it hold pressure.. it really should.

my test involves disconnecting the ignition.. so no sparks are created. disconnect the fuel line at the carb.. extend it into a clean clear soda bottle. have somebody crank the engine for a timed 15 seconds while you observe the fuel pulses into the bottle.



if your fuel pump is working perfectly.. the pulses should start as soon as you start cranking and the pulses should not diminish.. there should also be no bubbles in the pulses.

i have been fighting with sediment getting into the fuel pump and holding the check valves open allowing the fuel to drain back to the tank.. as soon as the engine stops.. this can also cause vapor lock issues.. where the fuel pressure to the carb held in the that line by the output check valve is reduced.. this allows the fuel pressure to be reduced at extended idle the fuel can boil and expand as vapor pushing the liquid backwards out of the pump .. this leaves the carb fuel level low..

i have also found cars that failed the 15 second full flow cranking test horribly. started out full.. at 10 seconds it was down to a dribble then just drops.. one the fuel line was crushed by errant floor jack and jack stand placement. the other had a fuel line so full of sediment that i would pull 23 inches of vacuum on the open line with my hand brake bleeder pump.. as we were not in a position to change the clogged fuel line. i pulled out a speedometer core and a variable speed drill and like using a plumbing snake routed out the clogged line..

the reason i do 15 seconds is you want to test the entire fuel suction system.. from the pickup in the bottom of the tank to the pump itself.

there have been a few other odd issues.. improperly hooked up fuel tank vent hoses.. where vacuum has been run to the tank.. causing suction that will fight the fuel pump for every drop of fuel.. this usually makes noise at the fuel tank.. creaking and groaning.. but not always..

i normally install a 10 micron fuel filter directly before the fuel pump. then perform the full flow cranking test 3 times in a row to allow the fast pulses of fuel to blow the sediment out of the check valves. then i hook up the carb.. get the engine started.. use a pair of Long nose pliers to squeeze the fuel hose closed between the new filter and the pump inlet.. while i bring the engine to fast idle with my other hand. when the engine starts to run out of fuel and stumble.. i release the pliers allowing a full flow pulse of fuel thru the pump and lines right thru the wide open needle and seat.. this i do twice..

this has diagnosed and solved the issues for me.. it really only takes a few minutes to perform.

oh... disconnect the fuel line to the carb.. blow into the line.. you should NOT be able to blow bubbles in the fuel tank.. if you can then you have sediment issues.
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Old 10-20-2016, 12:23 AM
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Vinniekq2: I sprayed the entire carb with Brakleen. HEI ignition, with a new coil. I could use the old one from 5 years ago. But that doesn't change the fact I'm not getting fuel to the carb.
Mousefink: I'll pull the plugs and check them. I'm pretty sure I gapped them at .035. I did replace the ignition wire from the firewall to the distributor cap.
OldTech: it's an old carb. It came with the engine that was running when I pulled it. The exhaust is from about 10 years ago, and looks to be in good shape.
EricNova72: I replaced the sending unit before I reinstalled the tank, figuring that the old one was pretty roached. I'll see about blowing air through the line and leaving it connected to the tank to see what it does.
4_Jaw_Chuck: I used about an entire can of Brakleen on the carb trying to clean it, but nothing changed.
Waynep712: After I cranked on it, it held at 7psi for several minutes. I've checked the line for crushed spots, or signs of issues to no avail.
Hoping for a slow night at work tonight so I can check it out. Last night was pretty busy.
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Old 10-20-2016, 12:59 AM
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Just went to the car, pulled the fuel line from before the pump, and blew it into the tank until I heard the tank getting air into it for a few seconds. I stopped, let the pressure dissipate, then repeated myself. Pulled the air hose away, and fuel came GUSHING out, so I plugged the line in. Let the fuel dry then fired it up. Just took it around the block and pissed some neighbors off! Looks like it was either something still in the line, or the sock. I'll give it a few days or even weeks and if nothing persists, I'll figure it's fixed. Otherwise I'll drop the tank and see what it looks like in there.
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Old 10-20-2016, 02:01 AM
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Just got it around the block again and the stumbling is back. Looks like I might pull the tank again like EricNova72 mentioned.
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Old 10-20-2016, 08:20 AM
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You should never pressure wash the inside of a fuel tank. Leaves crap everywhere inside that slowly comes back to haunt you!
Steam clean it!
Then air dry thoroughly with a strong air flow.
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Old 10-20-2016, 11:14 AM
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I purcháed a new fuel tank a month ago for my 1962 Chevrolet but have not replaced it yet. It is on my "to do" list. My 1962 Chevrolet 327/300 is a Oklahoma "barn find" , the engine was rebuilt in 1986 and 50k miles put on the motor until it was parked in 1990. New Ciadella green interior and Surf Green repaint was done in 1991 but it remained in the storage garage until 2012.
My 1962 Chevrolet Bel Air has sat unused in a garage for 22 years, from 1990 to 2012. The fuel system is full of dislodged rust particles. The intermediate neoprene fuel line hose connections on the frame are in poor condition. and will be replaced. I would prefer to replace the steel 3/8" fuel line from tank to pump but that is a difficult job on jack stands. I think I will blow the line out with compresses air. The 1959-1964 Chevrolets have a three piece fuel line with two intermediate neoprene connections. One behind the right front tire and one in the X-frame near the driveshaft carrier bearing. Those neoprene lines get brittle and degenerate. They should be replaced regularily when the fuel system is serviced.

That is a poor design and you should be glad your vehicle is not like that.
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Old 10-21-2016, 07:20 AM
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I think I'm gonna pick up some B-12 Chemtool in the gallon cans, then dump it into the tank, along with a short piece of chain, then load it up onto my work truck (I drive a tow truck, so I get some perks.) and try to slosh that stuff around to see about cleaning it. Then I'll drop the tank, and see what lurks inside.
I might end up having to replace the fuel lines as well. I'm really hoping to avoid replacing the tank all together
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Old 10-21-2016, 08:38 AM
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Maybe try a marine style fuel tank hooked up first to see if it really is your tank and lines is the problem.

Could save dropping yours.
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Old 10-22-2016, 02:56 AM
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I guys I could run an external tank and see if that helps, but so far, all signs are pointing to that
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