Plug pics. Tuning help needed, metering rods and jetting question

[Evan Frucht]

Hi I have an Poly 318 engine.

- The camshaft has a mild regrind from PO (based on what he told me, I can tell it has more cam than stock but the specs are unknown.)
- The car has a 2.5 inch dual exhaust with X pipe attached to the stock manifolds.
- Factory 4 barrel cast iron intake
- Later model Carter AFB 650
- Stock points ignition.
- NGK V-Power XR5 spark plugs ... MSD red wires

The engine recently started misfiring randomly and under load. It didnt feel right. I've been trouble shooting the last few days checking various things.

Then today it wouldnt start. I must have screwed up because when I pulled the top off the carb now one of my metering rods is bent I think it was causing the engine to flood. Hence the no start.

Anyways I'm trying to atleast get the engine started so I can finish adressing my tuning gremlins.

I figure this would be a good time to evaluate my current jetting since I need a replacement metering rod. The car has always ran OK with the jetting it came with, but I want to get it better if I can. I have never actually changed or even evaluated the jetting, the PO did it and it always run fine so I didnt mess with it, but i think it could be better and I dont fully trust the random guy who sold me the car... lol


Basically I'm wondering what size main jet and metering rod I might need. The old one is numbered 7147. The main jet says 400 and the other jet says 375. Would it be easier just to change the metering rod right? How often do main jets "wear out?"

Heres the plugs that I've been running for about a year. You can kinda see the numbers next to them. First picture... from top 1,3,5,7. Second pic 2,4,6,8. Third pic is number 7 which looked the worst to me but what do I know.

What do they say about my jetting and/or plug temp? A bit to rich? Other than the number 7 they are not covered in carbon deposits. They are a dark brown blackish color tho.

 

[Evan Frucht]

Also one has something that doesnt look great to me... Seems like the plug may have been arcing or leaking or something. Its number 1 plug

 

[Evan Frucht]

Any idea's?

 

[Don Frelier]

The arcing spot is weird.
Yes they look rich but if you had a bent metering rod then you really can't read the plugs until that is corrected.
The 7147 is the standard metering rod.
But you could have a problem with your float setting or the metering rod springs could be too stiff.
No primary jets don't wear out.
Some light reading.
https://www.hotrod.com/articles/mopp-0304-af-carburetor-reviews-and-tuning-parts/

In the future if you are taking the top off remove the metering rods first.
Install the rods last.

 

[RJRENTON]

IMO...
The carb you noted must be a Carter/Edelbrock (aka Eddy) # 1805 Consider looking ar Edelbrock carbs tuning guide www.edelbrock.com select ftom menu. Its a 79 page file with just about all variations of their offerings.
You definitely have mixture issues.....extremely rich rich. My guess is floats not shutting off possibly due to high fuel pressure or a damaged float. Since this a relatively new problem its not likely metering components but an internal leak. Poly engines are not hard on plugs and the number suggested are a good heat range.
YES....take out the metering rods first and reinstall them last and no, main jets do not wear out. Let us know how you make out....
BOB RENTON

 

[Evan Frucht]

The arcing spot is weird.
Yes they look rich but if you had a bent metering rod then you really can't read the plugs until that is corrected.
The 7147 is the standard metering rod.
But you could have a problem with your float setting or the metering rod springs could be too stiff.
No primary jets don't wear out.
Some light reading.
https://www.hotrod.com/articles/mopp-0304-af-carburetor-reviews-and-tuning-parts/

In the future if you are taking the top off remove the metering rods first.
Install the rods last.

The car has not been run with the bent needle. I must have messed it up the other day trying to put the top back on without removing the metering rods first. Live and learn.

... so the plugs should be an accurate indicator of how it was running.

Good advice about removing those rods first. I dont know why I didn't do that. I will remember from now on.

The car started having some issues come up out of nowhere recently. But before that it has always run fine as far as I can tell. I just thought there might be some room for improvement as far as jetting/tuning. I dont know how much thought the PO put into it when he set it up.

 

[Nate S]

Looks sloppy rich

 

[Evan Frucht]

IMO...
The carb you noted must be a Carter/Edelbrock (aka Eddy) # 1805 Consider looking ar Edelbrock carbs tuning guide www.edelbrock.com select ftom menu. Its a 79 page file with just about all variations of their offerings.
You definitely have mixture issues.....extremely rich rich. My guess is floats not shutting off possibly due to high fuel pressure or a damaged float. Since this a relatively new problem its not likely metering components but an internal leak. Poly engines are not hard on plugs and the number suggested are a good heat range.
YES....take out the metering rods first and reinstall them last and no, main jets do not wear out. Let us know how you make out....
BOB RENTON

I had thought it was a Carter AFB. I think the two carbs share some parts? Idk. It says 9636SA 0670 near the base. You can see where it's stamped in the last pic

 

[Evan Frucht]

Looks sloppy rich

Would you change metering rods?

Is it just a matter of adjusting idle?

How do I know what is causing the rich condition. Is it the... idle circuit ? Main jet? Secondaries?

 

[Evan Frucht]

Would changing from my 7147 to a 7352 rod be too big of a jump? Assuming it was running on the rich side I wouldn't mind leaning it out for more economy/power. But I also dont want to go to lean and damage anything.

 

[Ski 61701]

That carb is probably mid 80s vintage when Carter got bought out by Weber. A good carb overall. Yes its running rich. It can be a couple of things.
First off, did you make sure your distributor is working correctly, vac advance works, advance mechanism moves freely and counterweights move as well.
Other wise you are chasing your tail on this. Get ignition system ironed out.
Do compression test now see what shape the cylinders are.
regarding the carb, straighten out the metering rod. check floats and reset the level and drop, check needle and seat make sure they function.
There are several Carter/ Edelbrock tuning guides out there.
If you want to putz with metering rods go one step thicker. I would get a metering rod spring kit. I bet you have orange springs in it. Once you get it running ok, with engine off loosen metering rod covers and shift them over a tad n snug up, with motor running the rods should be down and not fluttering if they flutter, put a lighter spring in and redo test.
Check your plug wires too. Everything has to work properly.

 

[Evan Frucht]

That carb is probably mid 80s vintage when Carter got bought out by Weber. A good carb overall. Yes its running rich. It can be a couple of things.
First off, did you make sure your distributor is working correctly, vac advance works, advance mechanism moves freely and counterweights move as well.
Other wise you are chasing your tail on this. Get ignition system ironed out.
Do compression test now see what shape the cylinders are.
regarding the carb, straighten out the metering rod. check floats and reset the level and drop, check needle and seat make sure they function.
There are several Carter/ Edelbrock tuning guides out there.
If you want to putz with metering rods go one step thicker. I would get a metering rod spring kit. I bet you have orange springs in it. Once you get it running ok, with engine off loosen metering rod covers and shift them over a tad n snug up, with motor running the rods should be down and not fluttering if they flutter, put a lighter spring in and redo test.
Check your plug wires too. Everything has to work properly.

Ok thanks.
Before I bent the metering rod I found out my vac advance is not working on the distibutor and and currently waiting on a new distributor (supposed to be here tmrw)

The metering rod is bent pretty bad. I definitely will not be able to get it perfectly straight and true. I could try but I thought my best bet would be to just order some new ones so I can focus on any other problems I have (and not have to worry about a damaged metering rod effecting anything)

I will get a spring kit too.

The 7352 seems to be the next step up from 7147. With both the small and big portions getting larger. They have 7152 and 7347 too I think. I am trying to figure out what I should order.

 

[Ski 61701]

Ok thanks.
Before I bent the metering rod I found out my vac advance is not working on the distibutor and and currently waiting on a new distributor (supposed to be here tmrw)

The metering rod is bent pretty bad. I definitely will not be able to get it perfectly straight and true. I could try but I thought my best bet would be to just order some new ones so I can focus on any other problems I have (and not have to worry about a damaged metering rod effecting anything)

I will get a spring kit too.

The 7352 seems to be the next step up from 7147. With both the small and big portions getting larger. They have 7152 and 7347 too I think. I am trying to figure out what I should order.

Not sure on next size up on the rod but if it shows a tad thicker on both steps try that one.
Now is a good time to taking good notes.
I'd replace plugs check wires for resistance, once you do comp test, put it back together and see how it runs.
Another thing some people adjust the idle screw to a point where the blades uncover idle transistion slots inside the 2 front barrels. This usually happens when people try n compensate for excessive idle lope. You'd have to pull carb off and look up from the bottom to see if this is whats going on here. I bring this up because you said you have unknown reground cam in it. If slots are exposed it will be rich.
So I'd start at base timing and maybe advance it 2 degrees and then start your carb tweeking. you'll probably have to tweek your timing during this too.
Its a fine dance during tuning..

 

[Evan Frucht]

Not sure on next size up on the rod but if it shows a tad thicker on both steps try that one.
Now is a good time to taking good notes.
I'd replace plugs check wires for resistance, once you do comp test, put it back together and see how it runs.
Another thing some people adjust the idle screw to a point where the blades uncover idle transistion slots inside the 2 front barrels. This usually happens when people try n compensate for excessive idle lope. You'd have to pull carb off and look up from the bottom to see if this is whats going on here. I bring this up because you said you have unknown reground cam in it. If slots are exposed it will be rich.
So I'd start at base timing and maybe advance it 2 degrees and then start your carb tweeking. you'll probably have to tweek your timing during this too.
Its a fine dance during tuning..

Thanks for those tips. I probabaly did have the carb to rich. I was chasing a lopey idle for a long time. It would idle really slowly and very lopey. I recently found my my vaccum advance hasn't been working (for idk how long). I think I did have my idle adjusted way to rich and I also had my timing set at almost 20... probabaly felt ok becuase the vac advance wasn't doing anything.

Well... I have some work to do

 

[RJRENTON]

I had thought it was a Carter AFB. I think the two carbs share some parts? Idk. It says 9636SA 0670 near the base. You can see where it's stamped in the last picView attachment 1011814 View attachment 1011818 View attachment 1011820

The numbers shown in the first 2 pix are the individual casting numbers. The number stamped on the front side of the left mounting lug (by the orange hose), is the assembly's part number.
From your pixes, its definitely an aftermarket carb, as Mopar did not use a hot air choke assembly. You issue of s lopey rich idle mixture is NOT fixed with primary metering rod and jet changes or step up rod piston springs. ALL IDLE fuel and off idle fuel origionates and is controlled by the fixed metering orifices in the PRIMARY BOOSTER VENTURI ASSEMBLIES. These components are subject to plugging with dirt/fuel residue gum, especially the fixed air bleed orifices, which would cause a severe over rich idle and off idle condition.

Years ago, I had a 64 Dodge with a 318 poly engine, 727 trans, 3.23 rear. Converted it to a 4 bbl cast iron manifold from an earlier 318 engine. The carb I used was a Carter # 3854S from a 65 Barracuda Formula S car using the Mopar divorced choke assembly snd Formula S air filter assy. Perhaps you should consider something similar. Yes, PORTED vacuum advance is necessary for street operation and timing will depend on the engine's tolerance for the fuel you have available. Continuing to operate with an extreme over rich condition may lead to premature ring and bearing wear due to diluted oil. Just my opinion of course.
BOB RENTON

 

[Ski 61701]

Thanks for those tips. I probabaly did have the carb to rich. I was chasing a lopey idle for a long time. It would idle really slowly and very lopey. I recently found my my vaccum advance hasn't been working (for idk how long). I think I did have my idle adjusted way to rich and I also had my timing set at almost 20... probabaly felt ok becuase the vac advance wasn't doing anything.

Well... I have some work to do

At idle your vaccum advance is not really in play here, its when you accelerate is when vacuum is applied, it pulls on vac advance cannister to move advance plate.
Like Bob mentioned clean the idle screws passages make sure the idle screws themselves arent gouged up from overtightening.
The carb itself is set up for Chrysler kickdown n throttle linkage. Its more than likely a 625cfm carb which should be more than sufficient for your motor.
I'd pull the carb and look at where the idle transfer slots are in relation to butterflies. Hopefully they are not uncovered. Use your idle set screw and see how much ...or little adjustment you have left.
I would read up on adjusting Carter carbs, if I were closer, I'd loan you an old school carter tech book how to tune n adjust them.
If you can find some tuning info books like I mentioned highly recommend taking an hour or so and reading up.
Let us know how it goes

 

[RJRENTON]

Another possibility of uncontrolled fuel introduction (causing an extremely rich condition), MAY come from leakage of the plugged, drilled passages on the underneath side of the carb's base. These drilled passages connect the bottom of the main and secondary metering jet passages with their respective booster venturii wells. The same possibility exists at the primary accelerator pump well's drilled passsge. These plugged passages are subject to manifold vacuum and COULD introduce fuel if they are leaking. This is similar to an issue that plagued the GM Rochester Quadrajet carbs....uncontrolled over rich fuel mixtures, caused by a leaking drilled and plugged passage.
Just another potential problem area that needs to be eliminated.
BOB RENTON

 

[RJRENTON]

At idle your vaccum advance is not really in play here, its when you accelerate is when vacuum is applied, it pulls on vac advance cannister to move advance plate.
Like Bob mentioned clean the idle screws passages make sure the idle screws themselves arent gouged up from overtightening.
The carb itself is set up for Chrysler kickdown n throttle linkage. Its more than likely a 625cfm carb which should be more than sufficient for your motor.
I'd pull the carb and look at where the idle transfer slots are in relation to butterflies. Hopefully they are not uncovered. Use your idle set screw and see how much ...or little adjustment you have left.
I would read up on adjusting Carter carbs, if I were closer, I'd loan you an old school carter tech book how to tune n adjust them.
If you can find some tuning info books like I mentioned highly recommend taking an hour or so and reading up.
Let us know how it goes

IF the idle transfer slots are significantly uncovered, then they will feed fuel, that cannot be controlled by the idle mixture screws. Usually this issue comes to bear because of the cam's profile requiring a higher idle speed. The "fix" is to add bleed holes in the throttle plates, directly opposite the the transfer slots, approximately 1/8" diameter, half way between the throttle shaft and the O.D. of the throttle plates. This will allow the throttle plates to close furthur preventing too much fuel to be introduced yet contolled by the mixture screws. The 1/8" diameter hole is a suggestion....perhaps start out smaller gradually going larger until the desired effect is determined. Again, idle and idle transition fuel circuits are NOT adjusted by the metering jets, rods and step up pistons and springs. All of these points originate in the PRIMARY BOOSTER VENTURI ASSEMBLIES and are NOT NORMALLY USER ADJUSTED.
BOB RENTON

 

[Evan Frucht]

IF the idle transfer slots are significantly uncovered, then they will feed fuel, that cannot be controlled by the idle mixture screws. Usually this issue comes to bear because of the cam's profile requiring a higher idle speed. The "fix" is to add bleed holes in the throttle plates, directly opposite the the transfer slots, approximately 1/8" diameter, half way between the throttle shaft and the O.D. of the throttle plates. This will allow the throttle plates to close furthur preventing too much fuel to be introduced yet contolled by the mixture screws. The 1/8" diameter hole is a suggestion....perhaps start out smaller gradually going larger until the desired effect is determined. Again, idle and idle transition fuel circuits are NOT adjusted by the metering jets, rods and step up pistons and springs. All of these points originate in the PRIMARY BOOSTER VENTURI ASSEMBLIES and are NOT NORMALLY USER ADJUSTED.
BOB RENTON

Thanks,

Do I need to take the carb off to check the slots?

Or do I need to check it while it's on the car?

Does it matter if the car is actually running or warmed up when I check for this?

I'm a little confused about the how drilling holes in the throttle plates will help them close further? Isnt that determined by the idle speed adjustment screw ? Or both ? I'm trying to understand.

 

[RJRENTON]

Thanks,

Do I need to take the carb off to check the slots? YES would be easier to see them

Or do I need to check it while it's on the car? No not really....see above

Does it matter if the car is actually running or warmed up when I check for this? NO....to visualize the transfer slots is best seen by removing the carb

I'm a little confused about the how drilling holes in the throttle plates will help them close further? Isnt that determined by the idle speed adjustment screw ? Or both ? I'm trying to understand.

By drilling holes in the primary throttle plates will add additional air to the engine. By doing so, you will now be able to close the throttle plates, with the external adjustment screw furthur. By closing the throttle plates more, LESS if not all of the idle transfer slots will be covered or their area exposed to vacuum be reduced, allowing the existing idle mixture screws to be able to control the idle mixture more effectively.
Note, if you are contemplating proceeding in this direction, the suggested 1/8" diameter holes is a POSSIBLE STARTING POINT not a gospel number. It's always better to start small and gradually enlarging the holes cautiously, to prevent going too large. You will need to check for proper operation WITH EACH SIZE INCREASE. IF DRILLING IS CONTEMPLATED, make sure to support the throttle plates and shaft to prevent distortion during drilling, from the bottom side, cleaning all debris before testing.
BOB RENTON