Hey Guys, new to forum, but could use some help.
Got a 62' Chrysler 300, 383, Torqueflight.
Here's the issue:
Vehicle stumbles/backfires through the carb , upon acceleration.
Seems like it might be running lean(gas starved)
However, I've:
Dropped the tank, checked the pickup, removed the sock (which looked fine, changed the mechanical fuel pump twice, changed the electric fuel pump which I replaced the mech. with, twice, just put on a new Carter rotary fuel pump. Still seems to stumble.
I have a new 650 Edelbrock , on a bakelite carb spacer, which should eliminate any boiling off of the fuel, I've adjusted the timing, checked the new Mopar performance dist and orange module box.
It will idle, but when you put any load on it it stumbles, runs rough, starts backfiring through the carb.
Also did a compression check (fine), leak down check (fine), all rockers
and push rods are good. Engine only has about 1000 miles on it.

Any ideas ?
Thanks
Pappy

 

Sorry I am starting to learn Holley carbs but I know nothing about Edelbrock carbs. In a Holley I would start with the power valve then the nozzle and then the pump cam. Edelbrock has to have a tech line that's where I would start.

 

I would start with the VERY basics of tuneup



Do NOT assume that the timing mark is correct. Use a piston stop and verify it

Get or make a piston stop:

This is one I made for a small block over 30 years ago!!



Remove the no1 plug, make sure the piston is down, and remove the battery ground for safety. Install the stop, and rotate the engine until it stops against the device. You may have to adjust the length the first time you use it. You are NOT trying to stop the engine at TDC, but with the piston down from it somewhat.

When the engine stops, carefully mark the balancer directly below TDC on the timing pointer

Do the same thing, going CCW. When you are done you have two marks some distance apart. True TDC is halfway between, and if the old mark is accurate that is where it will be.

Next, make sure the ADVANCE mechanisms in the distributor are working, ESPECIALLY the mechanical advance. You should be able to "spring" the rotor the same direction as it rotates, and it should "pop" back without seeming gummy or sticking.

Carefully examine the coil, wires, cap, rotor for cracks, dirt, etc, and carbon tracking. With the engine running, pull one plug wire out of the cap while using a grounded probe to inspect the spark. Should be 3/8--1/2" long and nice and blue and snappy.

Consider using an ohmeter to check the wires, including the coil wire. Shake them while connected to see if they are breaking up internally

Use your timing light to determine if the advance is working while revving the engine. You can estimate timing out to 50-60 * by measuring carefully around the balancer and computing how much in inches 40* will be. Measure this off with your tape, then use dividers to create 10* marks. You can roughly check the accuracy of these marks by lining one up under the TDC marker. One other should then be under the 10* point.

WHAT IS your initial timing settng? You may just need more. MOST "stock" engines benefit from a SHORTER than factory advance curve, with MORE initial timing. My little 318 has the rough equiv. of a factory 340 cam, but is mechanical, so it is REALLY mild. I run the initial timing at about 15*, and about 36 total mechanical.

Last, check the carb idle screws, idle speed, and the accelerator pump shot

Get the engine nice and warm, and adjust the idle screws. Use a vacuum gauge or a tach, and move them OUT (left) until the engine drops, then slowly back IN (cw) until the engine peaks, and then just a touch MORE CW (lean). If they are off far, you may have to readjust the idle speed screw to keep things in reason.

Then, with engine off, using a flashlight if necessary, watch down the primary throttle bores, and move the throttle a little. You should INSTANTLY see the accelerator pump shot start. A quick "pump" should give a nice strong shot of fuel.

Use a vacuum gauge on manifold vacuum, to see how steady it is, and how high it is. If I can find it, there is an EXCELLENT animated webpage that shows different vacuum gauge readings.

 

frozen -

Before you go nuts, just check and recheck the firing order. You wouldn't be the first guy to make that mistake...

What 440 said us certainly possible, but an old diagnostic technique is to always run the simplest checks first, even it they have a lower probability than the more involved stuff.

Archer

 

Could be the secondary's opening too soon. They usually have a very good booklet about tuning.
You could probably down load a copy

 

i assume you checked the cam with a degree wheel it wouldn't bee the first time one was ground wrong
what is the history of the carb is it new old ? store bought or used new
i have recently purchased a edelbrock 650 av on a new motor 318
and have been tuning it.........1840 for 1805 1806 carbs
first try re-positioning the accelerator pump linkup one hole
also make sure the spacer is correct my edel says your spacer has to align with the throttle bores not an open spacer try removing it
you should also get the tuner kit for the carb check out my post ........ tuning my AVS....1840 for 1805 1806 carbs
the kit has a range of rod jets springs and have found the carb very tun able i had to rich en up the carb the carb had 95 prim 98 secd. with 68/57 rods the step up springs had to be changed im not sure what they had in it but now i run the 4 in. hg. 98 101 70/47 rod i'm sure your motor needs more fuel
if your carb is new use the calibration reference chart should have been in your box or down load it the manual and chart are very helpful

 

Check for vacuum leaks around intake.

 

Thanks for all the advice guys.
I'll try to clarify the story. Maybe it will help narrow down the problem. Leaving for a road trip about a month ago, tuned the vehicle, etc.
About a week before going suddenly the vehicle starts running lousy
(same kind of problem, stumbling, running rough) Take the carb off,
open it up, clean it out, back together. Car runs well for about 15 miles
then the same thing again. Frustrated, I go buy a brand new carb.
Car runs perfect. OK.
Leave for the road trip, about 300 miles in it starts to act like it's vapor locked, and quits. We check the carb, not getting any gas. We check the line to the mechanical pump, we got gas. We assume , bad fuel pump.
Difficult to change pump, on the side of the road, so we decide to put in
a small electric fuel pump from the parts store. Fires up, all is well, away we go.
Runs for another 500 miles, same problem. Check the outlet of the pump, no gas ! Change out the pump for a new one, fine. Here we go again.
200 miles later, same thing !!! OK, this is getting weird. Manage to limp it to repair garage, he thinks it's the wrong pressure pump. We change
to a lower pressure pump. No better, and now it's really running lousy
at load. Starting to backfire throught the carb, etc.
Still 200 miles from home, I decide to limp it back. Luckily I make it.
Then the story begins, change back to a new mechanical pump, same thing.
Do the compression, leak down tests, chk the rckrs, push rods, timing,electronic igniton, drop the tank, chk the pickup, remove the sock, change to a quality electric fuel pump.
Same damn thing. This should'nt be so complicated !!
Runs at idle, but once it's in gear and under load, its starts
running rough again ?
Don't know if this back story helps isolate the problem ?

 

Did a vacumn check, all is well. (By the way, while trying to get it running
it developed a coolant leak, turned out to be one of the Welch plugs in the head, took the head off, replaced plug, I only mention this
because now it's got a new intake gasket which would have cured any leakage, which I don't think there was anyway, around the manifold)

 

I have seen vacuum leaks into the brake booster . maybe you have a pin hole in the fuel line or is the tank vented , you could be creating a vacuum in the tank , does it suck in air when you undo the cap ?
Another thing that is common is the fuel pump pushrod , if it is worn it will not cycle the pump fully but you said you also tried an electric pump

 

that info hlps i would check for air being sucked into the fuel line from a rubber line which could have cracked and check the steel lines had a friend with a rusted line had the same symptoms of the idle but under power would run out of fuel

 

Yeah, kinda the same ideas I had, and have been checking for those exact
problems, but nothing so far.
This was a restoration done within the last year, I replaced all the steel and rubber pieces of the fuel line, so shouldn't be any problems there.
Have even resorted to running the car off of a small new coolant resovoir
to see if there was some restriction in the line, a little better but still
stumbles above idle.

 

Have you replaced the rubber connector lines in the fuel line?

I'd bet on dirt in the fuel system, all the way from the tank to the front,

Where is the electric pump mounted?

 

That was my thought, or a restriction in part of the line. Although it wouldn't explain it running for 500 miles just fine.
And the problem is when running it from a small tank in front, bypassing the fuel inie entirely, it still is stumbling. Which now make sme think it's not fuel related ? I switched the carb out from a running car with the same Edelbrock
and it has the same problem, while the car i switched my carb to runs fine.
So, that should eliminate the carb as an issue.

I also swapped out a orange Mopar electronic module and checked the distributor. Still not better !!
Now what ??????

 

check the reluctor gap in the dist , it should be .008 approx the thickness of 3 sheet of paper