1968 GTS 340 with Carter AVS 4966S

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Peini

Peini

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Hi guys, I just finished rebuilding my Carter carburetor for my 1968 Dodge Dart GTS with 340 engine. The carb is exactly a 4966S which should be for 1969 models I guess but please correct me if I am wrong.
I bought a rebuild kit from Walker and there was also a quite thick kind of base plate. This one was not in place when I removed the carb so I am not sure if I have to use it and if so at which position with respect to the gasket. Attached please find some pics of the plate, my intake manifold and the carb. Would be great if someone can help!
Thanks in advance,
Chris
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The thick gasket is a base plate heat riser gasket ( I know there is a better term for it but cant think right now)
, It is designed to help keep heat from the carb and improve drivability.

If you have been driving fine without it is would be safe to just use a correct base plate gasket. If you have had vapor lock or fuel boiling out of the carb between stops when the engine is how then using it might help with that.

Something to watch for is the choke pull down length. as the riser adds height to the carb the choke pull down might need to be in a different hole of bent straighter
 
Dana67Dart said:
The thick gasket is a base plate heat riser gasket ( I know there is a better term for it but cant think right now)
, It is designed to help keep heat from the carb and improve drivability.

If you have been driving fine without it is would be safe to just use a correct base plate gasket. If you have had vapor lock or fuel boiling out of the carb between stops when the engine is how then using it might help with that.

Something to watch for is the choke pull down length. as the riser adds height to the carb the choke pull down might need to be in a different hole of bent straighter
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Thanks for your help, I will use the base plate and see how it works. Where do I place it: intake manifold -> gasket -> base plate -> carb ?
 
1971 440
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BTW how I find this type of info is first googling the number, that took me to an ebay listing (not always correct but a start) then downloaded the 70-71 parts book from mymopar.com then searched the carb numbers till I found it.

a lot of time the numbers are semi sequential like a 4bbl for a 67 will start in the 43XXS range, 68 maybe 44XXS, and so on. it is not an exact numbering but can help find a place to start. (an example where the numbering does not follow what I said is the top line in the list above)

same general thing follows with mopar part numbers.
 
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Peini said:
Thanks for your help, I will use the base plate and see how it works. Where do I place it: intake manifold -> gasket -> base plate -> carb ?
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I think it is used inplace of the gasket at least that's how I have used them in other cars

manifold>riser>carb
 
Dana67Dart said:
I think it is used inplace of the gasket at least that's how I have used them in other cars

manifold>riser>carb
Click to expand...

Thanks, let’s see if I can get it running with the wrong carb. I just saw that the 4425S would be the correct one...let’s see.
 
as long as it will bolt on and the butterflies don't have interference AND the throttle linkage is correct for Auto vs Manual trans it should work. it will have more CFM and might be tuned different than a SB engine needs, but I bet your 340 will be OK with it.
 
Dana67Dart said:
as long as it will bolt on and the butterflies don't have interference AND the throttle linkage is correct for Auto vs Manual trans it should work. it will have more CFM and might be tuned different than a SB engine needs, but I bet your 340 will be OK with it.
Click to expand...

Tomorrow I will try and will let you know.
 
Good carb! I would NOT use the open spacer, use the thin base gasket.
Original jetting for the 4966 is 089 pri jet, 095 sec jet. 0655/063/058 rods

Original 4425 jetting is 089 pri & sec jet. 067/065/055 rods.

I wouldn't worry about the different jetting. These carbs were jetted for the fuels of yesteryear, try it & see. Edelbrock jets will fit in the secondaries [ not primaries ] if you want to experiment.
 
Thanks for all your replies and your great help, got it runnin after some adjustments :lol:
Took about 10 Minutes and it fired up. As suggested by Bewy i only used the thin gasket. After it heated up i adjusted idle speed. Runs good on all 8 cylinders, throttle response is really good but the idling is a bit rough and at higher rpm there was some backfire. For the first start I am really happy with the outcome, next weekend I will do some detailed adjustment.
Oh and choke is still not working properly now I am thinking about an electric conversion kit, let me know your thoughts on that.
Thx!
Chris
 
If you are using a stock cast iron intake I would use the correct choke and pull off for the AVS. The factory system is easily adjusted and you can dial it right in.
 
Peini said:
but the idling is a bit rough and at higher rpm there was some backfire.
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In neutral or when driving?
With factory cam should not be rough in either case, but even with cam, should be smooth in neutral.
Both the original '68 and the '71 carbs have a relatively lean idle. Lean fuel mix relative to pre-emissions control. So the engines were set up for slightly higher idle speeds. You might have to idle it closer to 750 rpm than 600 rpm.

Backfire through the carb can only happen if the mixture is igniting before the intake valve closes. Check the initial timing and then set it a two degrees less advance. See if that helps. If the distributor is original or correct, you can use the factory timing specifications. If its a generic replacement the timing increase for every few hundred rpm should be measured. After you plot the advance curve, then you decide on the initial.
 
That thick gasket will help with fuel percolation / fuel boil over which happens with todays fuels.
 
66fs said:
If you are using a stock cast iron intake I would use the correct choke and pull off for the AVS. The factory system is easily adjusted and you can dial it right in.
Click to expand...

Thanks, I am not sure if the pull-off is working correctly (does not seem so) and the divorced choke was not in place when i bought the car. If you add up those two the electric choke would be even cheaper and i thought it would be easier to handle.

Mattax said:
In neutral or when driving?
With factory cam should not be rough in either case, but even with cam, should be smooth in neutral.
Both the original '68 and the '71 carbs have a relatively lean idle. Lean fuel mix relative to pre-emissions control. So the engines were set up for slightly higher idle speeds. You might have to idle it closer to 750 rpm than 600 rpm.

Backfire through the carb can only happen if the mixture is igniting before the intake valve closes. Check the initial timing and then set it a two degrees less advance. See if that helps. If the distributor is original or correct, you can use the factory timing specifications. If its a generic replacement the timing increase for every few hundred rpm should be measured. After you plot the advance curve, then you decide on the initial.
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Thanks for the info, I only did the idle speed adjustment by ear so it might have been a little to low. I will defenitely check the timing :thumbsup:

On Sunday I did not want to bother my neighbours to much so I only did main adjustments since it is pretty loud. I hope to be able to continue this week.
 
if you still have a backfiring issue, tell us more about it: from carb or exh? Under what operating conditions?
 
Peini said:
Thanks, I am not sure if the pull-off is working correctly (does not seem so) and the divorced choke was not in place when i bought the car. If you add up those two the electric choke would be even cheaper and i thought it would be easier to handle.
Click to expand...

I have converted them using a Carter or Edelbrock AFB kit, for non factory manifolds. You will have to drill and tap one hole. I like the factory choke and pull off better. Pull off is easy. If it holds air you are good to go. If not it needs to be replaced.
 
66fs said:
I have converted them using a Carter or Edelbrock AFB kit, for non factory manifolds. You will have to drill and tap one hole. I like the factory choke and pull off better. Pull off is easy. If it holds air you are good to go. If not it needs to be replaced.
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Ok great because then the pull off is working. I tested if it would hold air before I put the carb back together. I just thought maybe it is not strong enough.
Well then I will add the divorced choke and see if if ti works.
Can you recommend a source to buy the divorced choke?

Thx.
Chris
 
I agree that its better to work with the factory non-electric arrangement if you can.
Tapping into the ignition circuit adds a big load on circuit that was never made for that.
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For both idle speed and timing a tachometer will be very helpful.
Looking in the '71 service manual the 4966 on a 440 was supposed to idle at 750 rpm with an AFR of 14.2:1. The idle mix screws worked in the normal fashion but had plastic caps on them to limit the adjustment range.

A '68 340 was was to idle at 650 (automatic) or 700 rpm (manual)

There's no reason for you to run the engine that lean. So you can experiment a little with the idle rpm and fuel mix that produces the most power. With an automatic that's easy to check by placing the transmission into gear and observing rpm or vacuum drop. The least is best.

Keep in mind that backing off the idle speed screw is not only reducing the airflow. It is also reducing the fuel contribution and increasing the air from the transfer port (slot). So if the throttle is slightly closed, and the idle mix screws aren't touched, the AFR will get slightly leaner.
 
Peini said:
Ok great because then the pull off is working. I tested if it would hold air before I put the carb back together. I just thought maybe it is not strong enough.
Well then I will add the divorced choke and see if if ti works.
Can you recommend a source to buy the divorced choke?

Thx.
Chris
Click to expand...

MOPAR-1970- CARB.NEW-CHOKE Challenger Barracuda Cuda 340 Carter- 4 Barrel-TH49 | eBay

https://quadrajetparts.com/divorced-choke-carter-p-2353.html

NEW Mopar 1968-69 383/440 1968-70 340 Carburetor Choke | eBay
 
Hey guys, short update: just came back from the garage, wanted to set the timing with my timing light but the light is not working so I adjusted the distributor without timing light and even with this simple adjustment it ran better. Better idling and no more backfire. I try to fix my timing light or get another one tomorrow. Oh and the choke pull-off does work indeed (saw it move).
 
Good Morning, yesterday I was finally able to set the timing after I installed the choke thermostat and got a new timing light. It took some time because there were thousands of other things to do (unfortunately not on my car).
Good news: choke set up now works great. I worked on the timing but as I set it to almost no early ignition the engine ran pretty rough, more ignition before TDC led to better running but i was not able to get the rpm down (hot engine not lower than 900rpm).
Bad news: engine got very hot and the radiator was boiling and leaking. I am not sure if the cooling circuit is working properly because it got so hot extremly quick. On the other hand the temp gauge only was in the first quarter, so I don't think this one works correct either.

To sum it up:
I am glad that the carb works including the choke set-up. Timing is fixable, cooling needs attention. Next steps: pulling the motor out and putting a new gasket kit in, new water pump, fuel pump, oil pump etc. and rebuilding the transmission.

Best
Chris

PS: During the carb rebuild i broke four different shaft screws which also led to some delay :BangHead:
 
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