Bought my first mopar 73’ Duster and the bottom of the air filter pan is black (right above the carb). Any tips on how the 4bbl should be adjusted

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tonyp25

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So I bought a 73’ Gold Duster. I believe it’s a 318 4bbl (still trying to confirm it’s not a 340 because it was cloned to look like it). I noticed that the air cleaner was scalding hot after it had been sitting for about 15 minutes and took some pictures. From a Reddit forum it looks like I should check the timing and tune the carb. Both things I’ve never done before.

I’m pretty mechanically inclined and work a lot on cars from the 90’s up. They pointed me to this forum and I was just looking for some tips. Also where would the engine block number be located on a 318 or 340? I am going to buy a heat gun today just to make sure I’m not exaggerating the engine temps.

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The thing is, if it's a 4bbl, it may have been re-cammed with a hotter cam, and therefore tune up specs don't apply. In fact a 73 was so "smoggy" (emissions restricted) that if the stock distributor advance is still in place, you can improve upon that greatly by installing a re-curved or aftermarket performance distributor. The "quick" way to this is an outfit called FBO ignition which offers a kit "limiter advance plate."

Generally tho, since you have a new-to-you car, you don't know the history, I would do some general diagnostics and tune up. Run a compression check/ leak down test to evaluate compression. Look at the plugs. Are they too lean, what is their heat range, and any signs of oil use. Does the car puff any smoke when revving, when "letting off" or when accelerating? How does the engine sound, generally, any noises that don't belong?

Then endeaver to check the timing, and try to graph the advance curve. Check initial timing with vacuum hose disconnected, Mark balancer if needed to determine higher RPM mechanical advance, and finally reconnect vacuum advance hose and wind it up and see what "high cruise" full advance including vacuum gives you. Note these numbers.

ADJUSTING CARB You can ONLY adjust carb idle speed an mixture AFTER setting timing, and AFTER making sure that the ignition system, cap, rotor, wires, plugs, etc are in good shape.

And the engine MUST be fully warmed, so if it runs "cold" you need to find the cause FIRST

With this done, and the engine warm, adjust the idle speed screw, over on the driver side carb linkage, to somewhere close to where you want it to idle. With a tach or vacuum gauge, adjust the screws first in, then out, to find highest RPM, highest vacuum. Go back and forth a couple of times. Then once you have found the "peak" just touch the screws so the idle does not quite drop, as you screw the adjusters in a tiny bit leaner.

Next, if this is an automatic. check the idle speed in drive. Be CARFUL, use a buddy to hold the brake, or block the tires. You may have to change the idle speed/ mixture to get this where you want.
 
Thanks for all the great info. I guess I'll need to find where I put my compression kit. I bought it from a guy I believe was the second owner. He's had it for 10 years and was in his 70's. He kept every receipt and had 100's of spare parts that he'd pick up wherever he went. He only drove it to car shows so he put on less than 200 miles a year. Spent most of the time I believe in his heated garage. So I think the car was well cared for before me.

I should've browsed this forum more because the engine block number was extremely easy to find. It's a 318. The original owner looks to have put a few factory 340 stickers in the engine bay and removed the Duster emblem in the rear to replace with a 340 twister sticker. Looks to be numbers matching for a Gold Duster except the 4bbl carb and Edlebrock manifold. Also opted to remove the bench seat and put Bucket seats in. It sounds great but it doesn't quite sound cammed to me (though it very well could be).

I'm going through the plugs this weekend. Didn't notice any smoke or issues yet. Drove it for about 45 minutes. It is an automatic. It was converted from the column to the floor (they saved all the parts). When I went over to test drive it the first time the tumbler in the ignition locked up. He had it towed to a local performance shop and I believe they put a whole new ignition in but I need to doublecheck the bill.

Your last sentence hits home because last year I was working on an 87' Monte SS trying to get the idle speed correct with a friend who is a full time mechanic. Almost put it right through my garage door.
 
Welcome to the site!
Great members here with tons of good info.
The more info you supply the better answers you will get. We love pics too. Helps alot .

67Dart273 knows his Sh*t and has helped me greatly over the years.​

Along with other members here. Ok now how did I make everything bold :rolleyes:
 
Thank you both! I took a few more pictures of the engine and interior. It’s raining where I am so once it stops I’ll pull it out of the garage and take some full shots of it. Currently just barely fits in the garage because I hadn’t planned on getting another car anytime soon but just kind of fell in my lap. Not sure what that wiring mess is under the steering wheel yet but it has led light strips outlining the bottom of the car so I figure that’s it.

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Engine displacement is on a smooth pad on front of block
as well as VIN. Casting number is on the side of the block
in a raised area but may be had to see.
 
67Dart273 said:
By the way if you don't have a factory shop manual, run over to MyMopar.com and download one for free. Some of the guys here, got it there.

Here's a link to the limiter plate kit if you are interested.

[/URL]
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Alright so had some more time today and bought an infrared heat gun. The Block never got above 190 degrees but the top coolant hose also never felt full (it was hot, 125 degrees but I could squeeze it, I guess I thought it would be so full of coolant I couldn’t squeeze it)

I think I have a timing issue. I had my dad start the car as I was looking at the carb with the air cleaner off. On startup there was a small *pop* noise and then a little plume of smoke came out of carb. Other than that it ran perfect and sounded good for the 35 minutes I had the engine on.

I took a few more pictures (somehow forgot the front of the car)…did it come stock with a coolant overflow? The radiator seemed full, coolant was clean but this overflow was nearly empty. Can’t seem to find what it should be filled at in the manual.

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Thats a coolant recovery system. The should be coolant in it along with a 10231 radiator cap.

The recovery system picks up excessive coolant when the car get hot and returns it when it cools off. It keeps the rad full all the time and keeps the nasty off the street.
 
Frank Mopar said:
Thats a coolant recovery system. The should be coolant in it along with a 10231 radiator cap.

The recovery system picks up excessive coolant when the car get hot and returns it when it cools off. It keeps the rad full all the time and keeps the nasty off the street.
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Thank you for the info! So it has some coolant in it but maybe only 1/2 quart (cold engine). I see that it looks like it can handle up to 2 quarts. Should I fill it a bit or does it need all that space for the potential hot coolant? Radiator itself if full.
 
Air cleaner lid is black cause of backfires. Get back with timing #s also hood clearance causes issues with a-bodys and people try and fix with drop bases like yours small height air filters etc. which act as a full time choke. Notice your vent tubes are removed to allow for that low profile system. Try and fit the highest air filter and test with puddy with hood closed for clearance. You may have engine issues causing backfires. Nice car, good luck
 
tonyp25 said:
Thank you for the info! So it has some coolant in it but maybe only 1/2 quart (cold engine). I see that it looks like it can handle up to 2 quarts. Should I fill it a bit or does it need all that space for the potential hot coolant? Radiator itself if full.
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Its ok but a tad more won’t hurt.
 
One of the "other" first things I'd want is to try and backtrack some of the car history and find out what is "in" the engine.......has it been bored, higher compression pistons, any head work, and what cam is it it and "has the cam been degreed?" After that I'd graph the timing of the distributor and if necessary see about recurving it.

When it idles is it your impression it has a "hot" cam? But you only want to evaluate that if you know it is in good condition, tuned, and running well, as engine problems can "make it seem" so

That looks pretty nice. You should have a lot of fun with it.
 
67Dart273 said:
Generally tho, since you have a new-to-you car, you don't know the history, I would do some general diagnostics and tune up. Run a compression check/ leak down test to evaluate compression. Look at the plugs. Are they too lean, what is their heat range, and any signs of oil use. Does the car puff any smoke when revving, when "letting off" or when accelerating? How does the engine sound, generally, any noises that don't belong?

Then endeaver to check the timing, and try to graph the advance curve. Check initial timing with vacuum hose disconnected, Mark balancer if needed to determine higher RPM mechanical advance, and finally reconnect vacuum advance hose and wind it up and see what "high cruise" full advance including vacuum gives you. Note these numbers.

ADJUSTING CARB You can ONLY adjust carb idle speed an mixture AFTER setting timing, and AFTER making sure that the ignition system, cap, rotor, wires, plugs, etc are in good shape.

And the engine MUST be fully warmed, so if it runs "cold" you need to find the cause FIRST

With this done, and the engine warm, adjust the idle speed screw, over on the driver side carb linkage, to somewhere close to where you want it to idle. With a tach or vacuum gauge, adjust the screws first in, then out, to find highest RPM, highest vacuum. Go back and forth a couple of times. Then once you have found the "peak" just touch the screws so the idle does not quite drop, as you screw the adjusters in a tiny bit leaner.

Next, if this is an automatic. check the idle speed in drive. Be CARFUL, use a buddy to hold the brake, or block the tires. You may have to change the idle speed/ mixture to get this where you want.
Click to expand...
Alright, so I’ve made it to the timing portion of your list. First time doing this but I watched a bunch of videos and bought a nice digital timing light (that shows RPMs too).

Going to try it out tomorrow. From what I read on this forum it seems like for a stock 318 it’s right around 6-8 BTDC and then a high performance one would like 8-10 BTDC. Granted mine has the edelbrock manifold and 4bbl Holley so I’m not sure which to go with.
 
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tonyp25 said:
Alright, so I’ve made it to the timing portion of your list. First time doing this but I watched a bunch of videos and bought a nice digital timing light (that shows RPMs too).

Going to try it out tomorrow. From what I read on this forum it seems like for a stock 318 it’s right around 6-8 BTDC and then a high performance one would like 8-10 BTDC. Granted mine has the edelbrock manifold and 4bbl Holley so I’m not sure which to go with.


I also found a receipt for a mild cam but I’m not positive the receipt goes to this car. If it did have a mild cam any idea would BTDC would look like? Below is a picture of the cam paper and I added a link to what I believe is the comp cam.

COMP Cams 20-210-2 COMP Cams High Energy Camshafts | Summit Racing

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Those timing numbers are a good starting point, but the engine may want something different. Often times they want a few degrees more. There are lots of posts in this forum about how to set the timing for best results. As has been said earlier, get your timing right before messing with the carb too much. Advancing the timing will cause the idle speed to increase, so you'll need to reduce that accordingly. You'll have fun with your Duster and as you learn how to "make it happy", you'll have a great sense of satisfaction.
 
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