69GMC - Lack of Secondaries/Low High-End Power

[RhapidFyre]

Just finished restoring the basics of the engine to get the whole thing back up and running. Flushed the fuel lines, replaced coolant, replaced the thermostat, got a brand new Edelbrock carburetor, set the timing, and the truck runs beautiful at idle.

First Drive Result:
Truck isn't shifting properly, fine, I'll adjust the kick-down as I see fit.
Transmission isn't shifting appropriately. Found out I forgot to fill the fluid. Works fine now. Shifts appropriately, no lagging/clanking anymore.

Second Drive Result:
Automatic (D): Hit the gas from a dead stop. A slight response lag, RPMs fell quite low, but it moves and not 2 seconds later it's taking off. Up to 40 MPH, secondaries roaring. Truck shifts to second. Initial power is good, climbing to 55. At almost exactly 55 MPH, the RPMs start to fall, it starts to chug, and struggles to maintain 55 MPH. It shifts to third gear, and all power is out the window. I'm losing speed at this point.

Manual (L1->L2): Hit the gas from a dead stop. Immediate response, truck takes off like it's a newborn. Screaming secondaries all the way up until I feel uncomfortable (around 45MPH), and then shoved it up to L2. Truck shifts immediately to second gear. Right around 60MPH, no secondary kick in. Truck's still running on low-end, holding 60MPH. No struggling, no chugging. Refuses to go any faster, and it does NOT appear the secondaries are engaging. I put it up to D, it shifts to third instantly, all power is gone. Struggles, falls down to 40 MPH and almost dies. I throw it down to L1 at 35MPH, instantly shifts to first gear, secondaries kick in, truck is at a high RPM. Roars when I hit the gas.

I'm completely at loss for what to do. I ruled out the transmission, because it's shifting immediately and appropriately. I ruled out the carb, it's brand new (750cfm). Secondaries open and roar at idle and first gear, but second and third are killing it's momentum.

Father in law believes it's the distributor, so he wants to exchange it. We have yet to do so, but I wanted to post here to farm ideas incase I am missing something.

Thank you!

[morepwr]

I would check the timing to make sure it is advancing when revved up. I would also verify the vacuum advance on the distributor is working (if equipped) If it does, also make sure the vacuum advance is hooked up to ported source on the carb meaning it gets vacuum once the throttle starts opening and not constant vacuum.

[ncpetersc]

HEI or points?

[RhapidFyre]

Originally Posted by ncpetersc

HEI or points?

Not entirely sure, I'm learning mechanics as I go along - Everything is stock/original except for the carburetor I put in.

[ncpetersc]

I'm on the learning curve as well, but have already received amazing advice from the guys on this site.

I was keying on the replace the distributor idea. I've been read up them. And if you have the original points, it sounds like they need some attention from time to time. So you may not need to replace the entire assembly, but could replace the points and condenser inside. I just picked them up for about $15, haven't replaced yet as I had other issues it turned out.

But if it's ignition/timing related problem, maybe inspect them?

I'm sure someone will have better more educated advice.

[RhapidFyre]

So I checked with the mechanic father in law, mine has HEI. We replaced the vacuum advance, and the two advances in the distributor, and the truck is acting even worse now. It's actually stalling as we drive it.

Hoping to find the timing gun to get the timing right again but won't be able to get back on the truck for a week.

[geezer#99]

Did you know eddy carbs don’t like more than 5 psi fuel pressure.
Yours is likely flooding a bit.
You’ll need a fuel regulator to fix it.

What do you mean by ‘the two advances in the distributor’?

And if you have an hei, is there a dedicated 12v to it?

[RhapidFyre]

Originally Posted by geezer#99

What do you mean by ‘the two advances in the distributor’?

He called it the advance, two hook-shaped plates that open up when the brace underneath is pushed.

I'll run the fuel regulator by him. Flooding the engine could be the problem, if the eddy can't handle the fuel pressure.

[firedemon]

im betting he means the weights under the rotor

[firedemon]

those higher rpms between 2 and 3 are pumping way too much pressure to the eddy going to have to fix that first before any timing or carb adjustments

[davepl]

How do you KNOW no secondaries are kicking in? How do you know it's an airflow problem and not a fuel delivery issue?

Really sounds to me like you're running out of fuel. You can repeat the test but get up to 45mph leisurely and THEN do your roll to 55 and I bet it works just fine. If so, come back and find me!

It's been done as a crutch, but I'd never put a regulator on a mechanical, stock style pump. Nor have I ever needed one with an Edelbrock carb. If a mechanical pump overcomes the needle and seat pressure, you need to up the spring rate on the needle and seat to fix it, not bandaid the fuel supply, but since I don't think that's the problem, likely neither needs to be done yet.

Still, there's a lot of merit to the theory because a mechanical pump gets driven harder at higher RPM so -could- in theory overpressure at high RPM only. But when you see hoofprints, think horses before you start looking for zebras!

[HO455]

What Edlebrock carb do you have? Did you properly tune the jetting of the carb after installation? If not look up the steps in the manual. Aftermarket carburetors may be in the ball park but for most folks that's as good as it gets. What carburetor did you replace with the Edlebrock? If it was a Q-jet you will never get that same feeling from an Edlebrock due to the smaller secondary bores. Big secondarys! One more reason to love the Q-jet.

[RhapidFyre]

Originally Posted by davepl

How do you KNOW no secondaries are kicking in? How do you know it's an airflow problem and not a fuel delivery issue?

Really sounds to me like you're running out of fuel. You can repeat the test but get up to 45mph leisurely and THEN do your roll to 55 and I bet it works just fine. If so, come back and find me!

It's been done as a crutch, but I'd never put a regulator on a mechanical, stock style pump. Nor have I ever needed one with an Edelbrock carb. If a mechanical pump overcomes the needle and seat pressure, you need to up the spring rate on the needle and seat to fix it, not bandaid the fuel supply, but since I don't think that's the problem, likely neither needs to be done yet.

Still, there's a lot of merit to the theory because a mechanical pump gets driven harder at higher RPM so -could- in theory overpressure at high RPM only. But when you see hoofprints, think horses before you start looking for zebras!

Hey davepl - If I take it super easy on the throttle, it starts chugging/stalling out at around 55, when the RPM's of 2nd gear start getting higher. Third gear is just... Dead. There is never a problem at idle or in first gear. Once it shift to second, I wanted to test what you said so I eased on the throttle, and it starts stalling around 55 MPH. - I backed off the throttle, and let it come down to about 40 or so again, and reapplying the throttle just continues the stalling. It seems the only way to get out of this "stalling rut" once it starts, is to lose so much speed that It'll shift down to first without slamming on the pedal. Once we fix the newest issues I'll take some videos for you guys of what's going on. We messed with the timing when we changed the advance and couldn't find his timing gun, so the truck is barely limping now.

Always something new

[68 P.O.S.]

What is your timing set at? Enigine a stock 350?

[RhapidFyre]

Originally Posted by 68 P.O.S.

What is your timing set at? Enigine a stock 350?

I believe we had it set to 12 BTDC. I could be wrong. It's way off now, buying a new timing gun this week to work on it more this weekend.

Engine block is definitely a 350, my father-in-law verified that on Day 1.

[RhapidFyre]

We are throwing a fuel regulator on it and fixing the timing on Friday/Saturday. Thanks for the feed back. I'll give a report on it this weekend.

[68 P.O.S.]

Sounds like a plan. Keep up the good work and keep us posted.

[RhapidFyre]

Placed the fuel regulator. Truck idles fine but dies as soon as you give it gas. Fuel filter is completely bone dry until the truck is started again. I can barely let it idle to keep it alive. I can rev it up in idle but under load its toast.

Restarting the truck and idling refills the fuel filter. If I shift to drive and go, it dies and the filter is empty

Gas Tank > Fuel Sender (NEW) > Fuel Lines > Fuel Filter > Mechanical Pump (NEW) > Fuel Regulator (NEW) > Edelbrock 4 Barrel 750 cfm (NEW)

Any help is appreciated at this point. Neither of us know what to do.

[geezer#99]

Check your timing!

What’s your fuel pressure set at?

[Grumpy old man]

Post a picture of your engine with the air cleaner off so we can see whats going on , A 750 may be too much carb for your truck who picked that ?

[davepl]

Originally Posted by Grumpy old man

Post a picture of your engine with the air cleaner off so we can see whats going on , A 750 may be too much carb for your truck who picked that ?

Not likely. GM built the 301 Pontiac with a 750cfm carb and you can run a 780 Holley on a 302 just fine. Assuming vacuum secondaries like a Q-Jet or 3310 of course...

Still sounds to me like it's running out of fuel. If this was me I'd stick a fuel pressure gauge on it so I could monitor it from the cab under load and see if it's falling off. Electrical, of course, don't plumb gas to the cab!

[RhapidFyre]

Originally Posted by geezer#99

Check your timing!

What’s your fuel pressure set at?

12 Degrees BTDC
Regulator is set at 5, also tried 2. Same results if not worse.

I'll get a picture of the set up, one sec.

https://drive.google.com/file/d/1vTc...w?usp=drivesdk
https://drive.google.com/file/d/1rYP...w?usp=drivesdk
https://drive.google.com/file/d/1mRJ...w?usp=drivesdk
https://drive.google.com/file/d/16qk...w?usp=drivesdk

[geezer#99]

I assume your 12 degrees is with the vac advance plugged off.

[RhapidFyre]

Originally Posted by geezer#99

I assume your 12 degrees is with the vac advance plugged off.

Correct, reattached after I was finished. Set to 12, set the idle, and then rehooked the advance and air cleaner.

Pictures added.

[geezer#99]

Where’s your pressure gauge?
You can’t go by the mark on that cheap totally unreliable reg you got.

What’s normally plugged into the open manifold vac port on the front of the carb?