Brand new carb-still problems, help?

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TAK65

TAK65

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Hi all,
my master mechanic installed the NOS 2 bbl carter 4958S (a 318 V8 version apparently) and also a NOS distributor in my Slant 225+automatic Dart today. Idles fine, acceleration is great BUT at certain rpm coughs and sputters just like all cylinders weren't firing or something. Loosening accelerator slightly brings it back to normal.
Previous carb+distributor combo had these symptoms too, anything from idle to higher rpms. Only felt like it started to run good only after 60 mph, then accelerated fine to 70 and up.

Plugs went really black. However the idle mixture is as lean as can be.

Any suggestions, anyone?
 
When was the last time it had a tune-up.?

Plugs, points(?), cap, rotor, wires. scope check?

Is the choke opening all the way, or wired open.?
 
Sounds like you may have a fuel supply problem. Pump, filter and sock all ok? I've had pumps with slack in the arm that barely pump at certain RPM then as they start slamming will move enough fuel to barely keep up.
 
inertia said:
When was the last time it had a tune-up.?

Plugs, points(?), cap, rotor, wires. scope check?

Is the choke opening all the way, or wired open.?
Click to expand...

Brand new everything. Timing is dead on. Choke is wide open.
 
mguner said:
Sounds like you may have a fuel supply problem. Pump, filter and sock all ok? I've had pumps with slack in the arm that barely pump at certain RPM then as they start slamming will move enough fuel to barely keep up.
Click to expand...

But don't pitch black plugs indicate too rich?
 
TAK65 said:
But don't pitch black plugs indicate too rich?
Click to expand...
Plugs cleaned from previous setup? Black is usually from too much fuel if not oily. Have you tried it with the vacuum advance plugged? Could be a breaker plate issue at part throttle vacuum too....
 
mguner said:
Plugs cleaned from previous setup? Black is usually from too much fuel if not oily. Have you tried it with the vacuum advance plugged? Could be a breaker plate issue at part throttle vacuum too....
Click to expand...

Brand new plugs. Not oily, just coal black and dry. Will try with no vac advance tomorrow. Thanks :)
 
"My master mechanic"

^^^^There's your problem.

Learn to do it yourself, or be forever plagued with these problems. Without knowing exactly what you have yourself, doing it yourself and reaping the rewards of accomplishment, you will likely be chasing your tail forever.

If he was your "master mechanic" he never would have returned your car running poorly. Think about that. Let it soak in.
 
TAK65 said:
Brand new everything. Timing is dead on. Choke is wide open.
Click to expand...

How do you know? Have you checked it yourself? Seen it with your own eyes?

I know. Your "master mechanic" told you the timing was right.
 
If your NOS carb is in fact a "rebuilt" carb, go get your old carb back.

I stopped putting rebuilts on a few decades ago cuz I usually ended doing more work to the rebuilt with little success, but managed to rebuild the old carbs myself with 99% success..
 
Does your carb look like this? or the Bottom one?
carterBBD-late1.jpg
Sounds like you could have stuck metering rods or they are not in the jets.
carter3.jpg
 
RustyRatRod said:
How do you know? Have you checked it yourself? Seen it with your own eyes?

I know. Your "master mechanic" told you the timing was right.
Click to expand...

Actually no. He was adjusting the distributor and I held the strobo light and watched the timing mark.
 
RustyRatRod said:
"My master mechanic"

^^^^There's your problem.

Learn to do it yourself, or be forever plagued with these problems. Without knowing exactly what you have yourself, doing it yourself and reaping the rewards of accomplishment, you will likely be chasing your tail forever.

If he was your "master mechanic" he never would have returned your car running poorly. Think about that. Let it soak in.
Click to expand...

I'm learning all the time. I was there with him the whole day, not just watching but also doing something and getting my hands dirty.
 
inertia said:
If your NOS carb is in fact a "rebuilt" carb, go get your old carb back.

I stopped putting rebuilts on a few decades ago cuz I usually ended doing more work to the rebuilt with little success, but managed to rebuild the old carbs myself with 99% success..
Click to expand...

No, it is NOS. I heard so many bad stories about rebuilds (thanks to FABO, mostly) that I was very aware of them.
 
mguner said:
Does your carb look like this? or the Bottom one?
carterBBD-late1.jpg
Sounds like you could have stuck metering rods or they are not in the jets.
carter3.jpg
Click to expand...

The old one was the upper, small hole in the butterfly valves. Throttle shaft bores all worn out.

The new one is more like the lower one with tag 4958S. But has the white plastic bowl vent.
 
I recommend getting a factory (not Haynes, Chiltons or other) Chrysler service manual for your car. SIt down and read it. It will teach you how to do everything. Then you can cut out the middle man. Not saying he's a bad guy, but it's like second hand information. If you learn to do it all yourself.......and these cars are VERY east to work on, you will learn more while saving money. It's a sorta win win.
 
sounds like a weak coil.

But yeah, the tune up starts with a compression test, and a valve adjustment.
No carb/dizzy work in the world can correct for mechanical issues relating to cylinder pressure leakage.
The tip-off here is that the problem was not remedied with the new parts.

I have to agree with the fellow who said something to the effect of having a 99% success rate in rebuilding old carbs. I have never in 47 years had to replace a carb on my junk. The only carb I ever replaced with a new part was on a Ford.I don't even recall what it was called. It was a gas-mizer carb of some kind, with variable venturis. The customer wanted it gone!
 
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I actually prefer the top design because they have a mechanical metering rod override that is adjustable. Many times rebuilders get parts mixed up on these. The carb kits available often don't include the correct gasket for the baseplate to body and the original has to be reused. There are so many variations of this design. You definitely need to pull the top off the carb and confirm metering rod position and operation. If the piston is stuck or the rods are bent or out of the jets you will have problems like you describe.
 
over the years I have found that until I replace all the 40 years old parts with good new stuff, seems there is always a problem arising. problem is NOW, so many times the new parts are junk!!! ha!..... like VR, coils, plug wires. even an NOS carb that is 40 year old can have problems.
but like RRR said, until WE ( as in you and I and everyone else), can diagnose and rebuild what we are working on, we are at the mercy of someone else! Ha
 
AJ/FormS said:
sounds like a weak coil.

But yeah, the tune up starts with a compression test, and a valve adjustment.
No carb/dizzy work in the world can correct for mechanical issues relating to cylinder pressure leakage.
The tip-off here is that the problem was not remedied with the new parts.

I have to agree with the fellow who said something to the effect of having a 99% success rate in rebuilding old carbs. I have never in 47 years had to replace a carb on my junk. The only carb I ever replaced with a new part was on a Ford.I don't even recall what it was called. It was a gas-mizer carb of some kind, with variable venturis. The customer wanted it gone!
Click to expand...

Tried two different coils (from a flawlessly working Valiant), same thing. Replaced ballast resistor. Valves adjusted, compression test very good and even pressures.
 
mguner said:
I actually prefer the top design because they have a mechanical metering rod override that is adjustable. Many times rebuilders get parts mixed up on these. The carb kits available often don't include the correct gasket for the baseplate to body and the original has to be reused. There are so many variations of this design. You definitely need to pull the top off the carb and confirm metering rod position and operation. If the piston is stuck or the rods are bent or out of the jets you will have problems like you describe.
Click to expand...

Thanks for this! He tore the old carb apart and there indeed was something messed up with the metering rods. Installed the carb and it is working well. Will eventually put the NOS one there as the old is quite worn out but it will do for the time being.
 
It may be possible to swap the newer base plate to the old carb. You will need to examine the gaskets carefully though and see if the passages are compatible. The lever for the metering rod arm may not have a hole to go in though.
 
had a quadrajet on a 67 GTO that had a bad needle and seat. Sometimes it would seat fine other times not. Was sometimes okay at idle, usually not. Before I figured the problem out and after filling the tank at the gas station it had saturated the oil in the pan with gas. After the fill up and cranking the motor at the gas station....BOOM!!!...result was an oil pan explosion ending with gaskets blown everywhere under the hood and a quarter sized hole in the #6 piston. it still ran after the explosion but there was a Pfft, pfft, pfft sound...the hole in the piston. I drove it 3 miles home. I was 17 at the time and didn't know what I know now at 56. It did exhibit the symptoms you have stated prior to the explosion. After you turn the motor off do you see fuel dripping into the carb? If so...look out!!!!
Pretty sure this isn't your issue but thought I would share a similar symptom experience.
 
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