1967 273 4bbl with Edelbrock 500 CFM Carb

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Crewdog89

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Hey guys,

So I purchased this vehicle about a month ago now and it was running kinda sluggish. I took out the spark plugs and noticed it was running rich due to the black carbon build up on the ends. Cleaned them up, reapplied dielectric grease and attached the plugs. I looked at the carb (Edelbrock 500CFM AVS 2 with manual choke) and decided to try resetting the idle mix screws and realized the guy 2 owners previous who did engine work to it had them out almost 5 full turns. Reset to 1.5 out and idle RPMs in park are around 800+\- 25 rpm’s. Once I throw it into any other gear though it shifts extremely hard .
I also noticed that the fuel filter is only half full it’s never been like that since I’ve owned it so not sure what’s going on. The bowl got down to half way when I had gone for a drive for like 20 min. As soon as I let it cool and turned the car back on again it was full so not sure what was going on. Fuel pump? I’m pretty new to engines this is my first project car so trying to focus on making her drivable and safe for distance. I attached photos and a video for reference.

1965 Barracuda
1967 273 4bbl
1965 904 TF transmission 3 speed

here’s a link to a video of the hard shift and the engine running. The lockdown linkage looks a little weird to me in the video again haven’t touched it it’s how it came from the previous owner.

Gofile - Free file sharing and storage platform

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The choke butterfly should be fully open. It sounds like you are on the right track with a basic idle mixture adjustment. It looks like your transmission linkage is properly adjusted. I don't know about your fuel filter. It could be a weak pump or a collapsed rubber line. Make sure you use regular gas if you can (non ethanol)
 
Dana67Dart said:
Alcohol in the fuel is boiling and displacing the liquid fuel.

1,000,000 options to solve the reason it is doing it.

And like aholes everyone has their opinion
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whats the most common and budget friendly option? I know make the filter go vertical along the fender wall and wrapping the lines in some heat tape is an option. @toolmanmike im going to go ahead and replace the pump anyways just in case. 20 bucks here at autozone donuts thank you for that!
 
I see you've got an Offenhauser Dual Port manifold on there. Not necessarily a bad thing, but they're VERY finicky with carb tuning. Just sayin'.
If I remember correctly, they like a real lean jet to go with the reduced primary port size...
OIP.x1lBSJWuQYK09UITNDTgWAHaFj?w=221&h=180&c=7&r=0&o=5&dpr=1.1&pid=1.jpg
 
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Why is the idle set to 800?

Lets talk about idle;
The faster it idles and/or the more idle-timing it has, the more power the engine will have at idle, and so
the harder it will bang when going from N/P to in gear.

The further the throttle is opened at idle, The more fuel will be discharged from the transfers. This will make the idle rich.
In compensation, you might think to close the mixture screws. That's fine, now it will idle. But as soon as you tip the throttles in, the entire slow-speed system is lean, because that system depends on the mixture screws being about in the center of their adjustment range.
The opposite is also true, namely; The more closed that the butterflys are at idle, the less fuel will be discharged from the transfers, and so in compensation, the mixture screws will have to be opened further. But now, as soon as you tip the throttles in, the entire slow-speed system will be rich due to the too-far open mixture screws.
There is a very narrow idle-adjustment window, in the which the transfers and the mixture screws are fairly optimum. If, at this setting the idle-speed is too slow or too fast, you adjust the speed with Ignition advance.
The more idle-advance that you give her, the faster she will idle. And
the less advance that you give her, the slower she will idle.
When all is said and done, you have to check your power-timing and make sure it is not so much as to cause detonation. You may have to modify the distributor to get that right.
Happy HotRodding.
 
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AJ/FormS said:
Why is the idle set to 800?

Lets talk about idle;
The faster it idles and/or the more idle-timing it has, the more power the engine will have at idle, and so
the harder it will bang when going from N/P to in gear.

The further the throttle is opened at idle, The more fuel will be discharged from the transfers. This will make the idle rich.
In compensation, you might think to close the mixture screws. That's fine, now it will idle. But as soon as you tip the throttles in, the entire slow-speed system is lean, because that system depends on the mixture screws being about in the center of their adjustment range.
The opposite is also true, namely; The more closed that the butterflys are at idle, the less fuel will be discharged from the transfers, and so in compensation, the mixture screws will have to be opened further. But now, as soon as you tip the throttles in, the entire slow-speed system will be rich due to the too-far open mixture screws.
There is a very narrow idle-adjustment window, in the which the transfers and the mixture screws are fairly optimum. If, at this setting the idle-speed is too slow or too fast, you adjust the speed with Ignition advance.
The more idle-advance that you give her, the faster she will idle. And
the less advance that you give her, the slower she will idle.
When all is said and done, you have to check your power-timing and make sure it is not so much as to cause detonation. You may have to modify the distributor to get that right.
Happy HotRodding.
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so much info to process! Haha definitely will take me some time maybe I have to take it in to get it professionally tuned for now. It’s hard because I don’t have the tools or the knowledge to complete it correctly. If I had someone who knew it all I would even be on their hip as they went through the process. Thanks for an avenue of approach!
 
Hey Crewdog,
I think these guys are the best of the best, end of statement! I've learned so much just in this post.
Thanks everyone. Crewdog, listen and think about what they are giving to us, it's knowledge. I know i am.
Thank you Gentlemen.
 
Couple of comments/suggestions.
- the Dual Port intake has small pri runners [ they are connected to the pri t/blades ]. They have high[er] velocity than conventional intakes & will make more tq at low speeds. So when the engine goes from N to D, it might be making [ as an example ] 70 ft lbs, where a conventional intake might be making 55-60 ft/lbs. You are going to feel that as a hard shift.
- unless the engine has a 'cam' in it, you should be able to lower the idle speed to 600, maybe even lower & reduce the shift harshness. Lowest rpm without stalling when braking.
- adjust idle rpm with the speed screw & mixture screws. Have the mixture screws about equal in/out. Adjust the mixture screws for highest rpm in gear [ wheels chocked ]. Do not use any other method, it will not work. If rpm is incorrect, change with speed screw & final tweak with mixture screws.
- pri jets/rods may need to be leaner with that intake.
 
Bewy said:
Couple of comments/suggestions.
- the Dual Port intake has small pri runners [ they are connected to the pri t/blades ]. They have high[er] velocity than conventional intakes & will make more tq at low speeds. So when the engine goes from N to D, it might be making [ as an example ] 70 ft lbs, where a conventional intake might be making 55-60 ft/lbs. You are going to feel that as a hard shift.
- unless the engine has a 'cam' in it, you should be able to lower the idle speed to 600, maybe even lower & reduce the shift harshness. Lowest rpm without stalling when braking.
- adjust idle rpm with the speed screw & mixture screws. Have the mixture screws about equal in/out. Adjust the mixture screws for highest rpm in gear [ wheels chocked ]. Do not use any other method, it will not work. If rpm is incorrect, change with speed screw & final tweak with mixture screws.
- pri jets/rods may need to be leaner with that intake.
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when you say In gear am I doing it in a specific gear or just drive? And sorry ha which one is the speed screw? Ha
 
The air screw adjustment should be adjusted as follows. Set the parking brake and chock the rear wheels. Start the engine and warm it up. Drop it in D once warm and get the idle speed "around" 650-700. Connect a vacuum gauge to a manifold vacuum port. I THINK that is the small port on the front of the carburetor, driver's side. Adjust each air screw to achieve the highest vacuum reading for each screw. Readjust the idle if necessary. Too many people get caught up thinking air screw adjustment should be X number of turns out, when in reality, the vacuum gauge is the way. I would run each screw ALL the way in and lightly seat them one at a time. If when that's done, the engine does not die or almost die, the carburetor is getting fuel form somewhere it's not supposed to and needs to be serviced. If it stumbles and or dies when each screw is turned all the way in, that's a good sign and go ahead and adjust as outlined. Good luck with it.

Also one more note......I agree that intake isn't the "best", but I don't believe that's the source of the problem. Also check the initial timing and let us know where that is.
 
Crew,
You can use any gear. The idea is that the engine needs to have the converter load on it.
The idle speed screw is on the main body, a single screw, on the driver's side, adjusted from the front of the carb. It just controls where the t/blades stop.
I am going to have to disagree with RRR about using a vacuum gauge. Not needed & you don't get the best result. The human ear is far more sensitive than a vac gauge. Screwing the mixture screws in leans the mixture & vice versa. Always aim for the leanest mixture screw setting that gives the highest/smoothest idle rpm. The highest rpm indicates that the engine is making the highest HP with amount of air & fuel being supplied by the mixture screws. If you turned the screws & rpm drops, engine is making less HP.
There is no particular idle rpm once you deviate from factory parts. As I said in post #9, adjust the speed screw for the lowest idle rpm that [a] the engine doesn't stall under braking & the engine sounds/feels comfortable. As an example, you might be able to go down to 400 rpm, but the engine might not sound happy that low, so increase slightly. Change in idle speed should be followed by checking/tweaking the mixture screws.
 
I am not very good with computers. This has happened a few times & I don't know what I am doing that causes this! Any ideas?!
 
Bold is the "B" above the reply box. You must have turned it on while typing.
 
Crewdog89 said:
I also noticed that the fuel filter is only half full it’s never been like that since I’ve owned it so not sure what’s going on. The bowl got down to half way when I had gone for a drive for like 20 min. As soon as I let it cool and turned the car back on again it was full so not sure what was going on. Fuel pump? I’m pretty new to engines this is my first project car so trying to focus on making her drivable and safe for distance. I attached photos and a video for reference.
Click to expand...
A portion of the fuel will vaporize summer engine temperatures. Fairly normal. its why the outlet of the filter needs to be higher than the inlet. This helps the vapors escape through the carb without pushing a bunch of fuel into the carb bowl. Chrysler explained this in a 1963 master tech booklet.

Speaking of which
Here's a fairly complete list.
Master Technician Service Conference - Chrysler's Training for Mechanics

when a link fails, I find its usually because they loaded the page as Jpeg and then linked as jpeg or visa versa.
Sometimes its easier to note the MTSC year and session number, then go to mymopar.com and get the filmstrip or booklet there.

hard shifting is also covered in those booklets and filmstrips. You'll want the ones pre '67 if you are using the original 904 and linkage.

As far as mixture adjustment at idle. First. the timing should be around 10 - 12 at something like 600 or 650 rpm. If the rpm is higher, then the distributor may be advancing. So lets say you set it at 10*BTDC at 800 rpm. When you slow the engine to 650 rpm you may find timing is then 8* BTDC. Follow? You need to adjust everything a couple times or more to tune it in. (all done with vac advance hose plugged with a golf tee or such)

The idle screws are adjusted by turning in 1/8 turn at a time until the rpm drops, then turn back 1/8 turn or so. It's easier to identify the engine performance falling off on the lean side than the rich side. So get the best running on the lean side in neutral/park , then make them a tad richer because when the engine is loaded (placed in drive) it will be stronger with a little richer than you found in neutral.
 
So used the timing light and adjusted for 600-650 in Neutral. Came to 3* BTDC. Is that normal? Vacuum advance is capped off
 
Crewdog89 said:
So used the timing light and adjusted for 600-650 in Neutral. Came to 3* BTDC. Is that normal? Vacuum advance is capped off
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I run at least 10° before. If you run too much it might ping unless you limit the total
 
So I set the timing to 11* BTDC. @ 3K RPMS I’m looking at 32-34 and with vacuum advance of 19 I’m looking at a tota of 51-53*. Does that sound about right?
 
Crewdog89 said:
So I set the timing to 11* BTDC. @ 3K RPMS I’m looking at 32-34 and with vacuum advance of 19 I’m looking at a tota of 51-53*. Does that sound about right?
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Sounds pretty good. You should notice a difference in performance.
Pinging is extra enging rattling during acceleration. Preignition,detonation.
 
Tuning a carb with a mixture screw is always a trial and error: Usually you get the engine up to temp (Important!) set float level (on a Holley its a sight glass) get a baseline in the screws: turn them all the way in (one at a time to prevent the car from dying!) just until you feel them seat and then unscrew each 2 full turns (just to get them equalized). Reset your idle speed back to 600 (example, use whatever the FSM for your year says in gear) now turn one mixture screw 1/8 turn out, then the other - note the RPM change. If it idles faster do it again equally. If it idles faster keep going in 1/8 increments! If its slower, go the other direction. Keep track of how many your out in turns. It will soon stop making any difference and then further you go in that direction will start making the idle go down STOP! revert 1/8 turn and then RESET idle speed with idle screw to 600 (example) and start turning the screws again, left and right in the same manner. your looking for the highest idle speed (or most efficient/power) . Vacuum readings will peak here too so if your using both gauge and tach, this will help. Once the screws do nothing one way or the other idle speed wise, and the idle speed is to spec, your about as close as your gonna get short of a wideband O2 meter or a sight spark plug where you can compare combustion color to a supplied color chart. On a stock 273/4, Putting the car in gear did nothing to the RPM's on that slow old SW "S" tach, iirc it was rock solid at 600. For a factory 'hot' motor, that 273/4 was very mild at idle.
 
Crewdog89 said:
So used the timing light and adjusted for 600-650 in Neutral. Came to 3* BTDC. Is that normal? Vacuum advance is capped off
Click to expand...
For a 67 without CAP, no.

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This comes from the 1967 Dodge/Plymouth Shop manuals. It may also be in the Operators Manual. I'd have to check mine to confirm that.

I've also plotted out the whole curve if set to the factory initial and using a factory distributor.
Timing Marks on the 273 [66 Barracuda]

Incorrect Timing Adjustment causing heat issues?
 
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