Carter bbd 1½ main jets

jct

jct

Senior Member
Joined
Jun 11, 2015
Messages
3,757
Reaction score
3,783
Location
indianapolis
On my 68 Newport 383 auto.
My my current carburetor I have on there I think it's off a 69/70 truck(I think). I bought it off of eBay some years ago. I don't keep track of time it all blurs together... Anyways it's causing me to run warmer than I like seeing at highway speeds around 205°f, city speeds every cools back down to around 180-185°ish. So I'm thinking I'm running lean at highway speeds. I have 3 other parts carburetors that includes my original that came with the car when I bought it back in '15. I have one set with 120-437s and two sets of 120-311s (which my original carb had) (I did see in my service manual states that the standard size is 120-314s) I'm not even sure what's in my current carburetor. So my question is what size jets should I run from my current stock?

And finding the correct size I need is non existent and buying more carburetors is a crap shoot on jet size

I set my ign timing with a vacuum gauge, which is set at 20 inches of mercury
 
Last edited:
Check the radiator core temps with an infrared non-contact thermometer. I highly suspect that parts of the core are clogged, not allowing enough heat radiation to happen at highway speeds. IF the carb is running too lean, the ceramics on the spark plugs will be more chalky-white in color, rather than the normal light beige color.

From about 1500rpm and up, the carb is on the main system, so if its too lean at lower speeds, it will be lean at higher speeds, too. But since you mention it cools back down at lower speeds, it would seem that the issue is elsewhere. Including too much ignition timing, which can lean the mixture a bit from what it normally would be.

Just some thoughts and experiences,
CBODY67
 
Lowering the vacuum, two-three inches of mercury via the timing makes my car bog down from a stop. I did flush my cooling system about 3 years ago, and I rarely drive my car, due costs and my fund are going elsewhere, can't exactly spend it on getting my radiator for next couple of years... (Trying to save up for a new daily driver, it's going painfully slow)
 
I agree with checking spark lug color. White indicates lean mixture. Cost to check $0.

On your question, the only jet you have that is larger than stock is 120-437. You may find after the change that the spark plugs are black and sooty from rich mixture.

Good coolant can break loose rust from the block. Bottle of Radiator flush is $5-$10. I would flush again before considering a new radiator.
 
I googled the number for the 120-437 and it said it's for a afb/thermoquad

Screenshot_20220908-044720_Foxit PDF Editor.jpg
 
Last edited:
jct said:
I googled the number for the 120-437 and it said it's for a afb/thermoquad

View attachment 556829
Click to expand...
Unless the spark plugs are white, I don't think jetting will correct the problem, regardless of the jet.

My opinion is the the cooling system is not working properly, such that during high heat at highway speeds, the engine is starting to heat up beyond normal. I would pull the thermostat and flush the system again, looking for rust to spew out. Afterward, I'd drain the radiator and engine at both block plugs. Then add new coolant.

Radiator shops used to flush radiators with good cores. I remember having one done for $40. Hard to find a shop to do that now, but you could try looking if the regular flush doesn't work. Good luck!
 
I don't have 20 1 gallon milk jugs saved up yet, and I go through a gallon every 2 weeks...
 
Unlikely lean jetting would cause engine temp to rise - is it way overbored? - but this is where a hand choke comes in mighty handy, sometimes a tiny bit of choke on long heavy pulls, especially on cold mornings, and also as a troubleshooting aid.

Vacuum leak?

Throttle shaft leakage is almost a given on most old carbs, but can it lean mixture out?
 
Loadrunner said:
Unlikely lean jetting would cause engine temp to rise - is it way overbored? - but this is where a hand choke comes in mighty handy, sometimes a tiny bit of choke on long heavy pulls, especially on cold mornings, and also as a troubleshooting aid.

Vacuum leak?

Throttle shaft leakage is almost a given on most old carbs, but can it lean mixture out?
Click to expand...
@jct has 20 inches of vacuum

Not sure what you mean on throttle linkage
 
Not throttle shaft linkage, but leakage, the air that passes around the gap between shaft and worn body on a throttle plate that hasn't been rebushed.

Can it lean out the mixture?

The ideal mixture is "stoichiometric"; 14.7 parts fuel to 1 part air.

"The stoichiometric mixture for a gasoline engine is the ideal ratio of air to fuel that burns all fuel with no excess air. For gasoline fuel, the stoichiometric air–fuel mixture is about 14.7:1 i.e. for every one gram of fuel, 14.7 grams of air are required."

Obviously an air leak, any air leak, will lean that perfect mixture out, and lean = hot because of the "latent heat" properties of gasoline*, it cools as it goes through the engine.

Anyone remember fuel coils packed in ice for racing, or water injection to replicate the improved volumetric efficiency of the better - denser - air from cool nights?

* The latent heat of vaporization (LHOV) for the fuel is the amount of required energy which changes the state of fuel from liquid to gas without a change in temperature. This parameter is expressed in unit kJ/kg, which is the value of heat energy to turn one kilogram of fuel from the liquid state to a gaseous vapor."
 
Loadrunner said:
Not throttle shaft linkage, but leakage, the air that passes around the gap between shaft and worn body on a throttle plate that hasn't been rebushed.

Can it lean out the mixture?

The ideal mixture is "stoichiometric"; 14.7 parts fuel to 1 part air.

"The stoichiometric mixture for a gasoline engine is the ideal ratio of air to fuel that burns all fuel with no excess air. For gasoline fuel, the stoichiometric air–fuel mixture is about 14.7:1 i.e. for every one gram of fuel, 14.7 grams of air are required."

Obviously an air leak, any air leak, will lean that perfect mixture out, and lean = hot because of the "latent heat" properties of gasoline*, it cools as it goes through the engine.

Anyone remember fuel coils packed in ice for racing, or water injection to replicate the improved volumetric efficiency of the better - denser - air from cool nights?

* The latent heat of vaporization (LHOV) for the fuel is the amount of required energy which changes the state of fuel from liquid to gas without a change in temperature. This parameter is expressed in unit kJ/kg, which is the value of heat energy to turn one kilogram of fuel from the liquid state to a gaseous vapor."
Click to expand...
Thanks. Reading comprehension would have helped here. I understood as soon as you pointed out what you actually wrote.
My bad.
DOH!!! (Homer moment. I need some Duff beer. Then I can cut a bar stool shaking fart that makes Barney fall out of his chair. Surely I'll be a better reader the next morning)
 
Got the system flushed and I added a coolant filter that doesn't restrict flow much unlike the ones you find off Amazon...

The one I bought

Aeroflow In-Line Radiator Filter / Filler, Black | Pegasus Auto Racing Supplies

This black anodized coolant filler mounts in your 1.5 inch (38mm) ID radiator hose. A filter screen and a sludge trap help to keep your system clean.
www.pegasusautoracing.com www.pegasusautoracing.com

If I'm stills having issues I'll remove the radiator to get it cleaned out properly next year
 
jct said:
Got the system flushed and I added a coolant filter that doesn't restrict flow much unlike the ones you find off Amazon...

The one I bought

[/URL]

If I'm stills having issues I'll remove the radiator to get it cleaned out properly next year
Click to expand...

Man, you're singing some VERY FAMILIAR blues here! After running a freshly rebuilt Carter BBD a few weeks, I'm sure glad we're upgrading to a 4 bbl intake w an Edelbrock 1405! I admit, once I'd replaced a very leaky Stromberg WWC w the BBD, engine temperature decreased a good 10 degrees F, and I finally leaned out the damned idle screws in a VERY non intuitive way to get a decent idle and run, but I beleive I'll try to avoid ever using a BBD again after the ordeal we had with a pair of them recently. There are a few basic issues in their construction I found not to my liking at all.

Anyway, we're blessed with an old Mopar 252 4984 which I had patched up and rodded this time last Fall, due to a severe shortage of decent quality 22" aluminum radiators at that time. Driving in town during the summer here inspires one to do the utmost to keep an engine running COOL. Aside from the vacuum leaky lean condition from that old WWC this past summer, everything else in the cooling system was and remains excellent. I installed an NOS Mopar fan clutch just a couple weeks ago too, AFTER noting how things had cooled down w the BBD a bit. We had resorted to a fixed 7 blade fan for a few weeks earlier. Yes, lean mixtures CAN warm things up a bit.

By December, I expect no need for any mechanical fan on Gertrude at all. We ran her last winter with nought but a modest A Team 16 inch electric pusher, which kicked on just during afternoons most days. But with April, a mech fan became desireable, and necessary by May, so I put one on for the summer.

Good radiator, then water pump, fan and thermostat, not to mention a CLEAN cooling jacket on your engine all make for a happy, well adjusted engine. Hope yours gets there and stays there.
 
You must log in or register to reply here.

Similar threads

carfreak6970
Timing issue 70 Polara
Replies
10
Views
783
CBODY67
C
Knebel
Shaking 360 LA
2
Replies
23
Views
2K
Knebel
Knebel
6
Carter BBD issue on 1966 dodge Monaco
Replies
14
Views
2K
tbm3fan
tbm3fan
70NewY’ER
Engine Bogging?
2
Replies
26
Views
3K
70NewY’ER
70NewY’ER
MoPar~Man
318 rough idle (20+ years in storage)
2
Replies
20
Views
4K
CBODY67
C
Back
Top