Technical Carb Gurus Needed - Carter WCFB Leaning Out at Part Throttle

Hello all,

My 53 Packard is having some issues and I figured with the knowledge on this forum, I think I just might be able to get this figured out.

So, here is the story. I picked up a 53 Packard last year that had been sitting for 30ish years. I had the tank gone through, I installed all new fuel line, fuel filter, electric transfer pump, a recently rebuilt mechanical fuel pump, rebuilt the carb, new base gaskets and carb insulator, new battery, new plugs, new wires, rebuilt vacuum advance, all new vacuum lines.

When I rebuilt the carb (Carter 4bbl), it was SUPER out of spec. It was also missing parts. I'm surprised it ran at all when it was parked. Anywho, I rebuilt it and adjusted everything per the factory manual. I'm super OCD and have rebuilt many carbs before, so I feel pretty confident in the rebuild (but ya never know, maybe I missed something).

When I first got her fired up, she had a pretty decent miss at idle. A neighbor told me it probably had a stuck valve or lifter and to put MMO in her. So, I replaced 20% of oil with MMO per their instructions. After driving her a few times in the last week or two, something definitely freed up because she idles a lot better now. She still has a small random miss that I need to figure out.

I've got her to the point where she starts up relatively easy, idles well enough, and gets down the road okay. The problem I'm having is a weird lean (I think) area if I slowly wind it up with no load on her. When I get to about 25-30% throttle, the carb makes a gnarly sucking sound and wants to die. If I quickly accelerate when she's about to die, the accelerator pump kicks in (I can see the fuel squirting) and she revs up great. If I rev her up real fast from idle, she revs up great all the way through and this issue doesn't show up at all.

The weird thing is, if I partially cover up the primary side of the carb and slowly wind it up, she continues to raise in RPM and sounds fine. I don't know if I'm covering up a vacuum leak or creating better vacuum because the engine might still have stuck valves or rings causing low compression.

When I cruise, it seems to be around this lean area and the car just doesn't seem very happy when cruising around. I have to kind of accelerate and let off over and over. It sucks to say the least.

What do you all think? Am I fighting a carb issue, vacuum leak, or low compression not pulling the charge in?

Thanks fellas,

-Chris

 

I think before I would voice an opinion, it would be nice to know the results of a compression test; followed by the idle vacuum reading and the RPM taken.

The engine calibration will be at its leanest point in the condition you describe. Anything that isn't up to snuff may make the calibration too lean. Testing eliminates variables.

Jon.

 

Hi Jon,

Thank you for the reply. I'll do a compression test today and update this thread with the results.

As for the vacuum test and rpm, the only vacuum line coming off the carb is a hardline going to the dizzy. If I remove that to test vacuum, will the vac advance not working mess with the reading at all?

It would be cool if it was a simple rubber line, then I could just tee off of it. Any ideas on how I should go about this?

The rpm is another issue, the car doesn't have a tach. I suppose I could use my timing light and a 12v battery on the ground to power it. Any thoughts?

Thank you,

-Chris

 

I have not seen all variations, but most WCFB's have a vacuum tap in the center of the back of the throttle body, often plugged with a pipe plug.

Maybe a friend with a dwell/tach test meter? It is a handy gadget to set your points correctly.

Jon.

 

Update: I did the compression test while the engine was cold, with the choke and throttle plates wide open. Here are the results:

1 = 125
2 = 115
3 = 115
4 = 120
5 = 125
6 = 120
7 = 125
8 = 115

The numbers look to be pretty even, but aren't they a little on the low side?

Thanks for the advice on the vacuum port and dwell meter, I'll check for that port here shortly and see if I can barrow a dwell meter from my neighbor.

-Chris

EDIT: I took a picture of one of the spark plugs but forgot to post it. All 8 looked like this one.

 

Chris - the compression ratio on your Packard is 8.0:1.

With a "clean" engine, good compression would be 140. Carbon deposits anywhere would raise the numbers.

Lots of carbon deposits on that plug.

Might be interesting to repeat the test, and before testing each cylinder, put a couple of teaspoons of engine oil in the cylinder to see if the numbers increase substantially.

Jon.

 

Ah, okay, so it is a tad on the low side. Are you thinkin' the rings might still be stuck a little?

Being that it's a flat head and the spark plug holes are right over the valves, do you have any suggestions or ideas on how to get some oil on top of these pistons?

Do you think the compression being where its at could be part or all of the reason I'm having this lean issue?

-Chris

EDIT: Congrats on 3000 posts btw! I just hovered over your avatar and saw it. What a trip!

 

Chris - I didn't know about the posts.

Still would like to know vacuum readings at RPM.

However, if it were mine, and I did NOT want to go into the engine at this time; I would rig a MANUAL choke on the carburetor. When the engine leaned out at cruise condition, I would give it just enough choke to alleviate the lean condition, AND DRIVE IT! Only use the choke when you need it.

A thousand miles, driven more than 15 miles at a time, MIGHT clean up the engine enough to clean up the lean out; or it may not. It sounds like you have plenty of power to enjoy the car if you can get by the lean out.

Personally, one of the dumbest things I have ever done as far as my own automobiles was to believe the internet about blocking the heat cross-over for additional power (on the street), and I created a monster!

At my age, my "heel and toe" technique is not what it used to be; and with an automatic choke, the engine died at every stop sign/light for the first 30 minutes. Adding a manual choke made the car extremely responsive, and after it warms completely, no choke needed.

Enjoy that Packard!

Jon.

 

I wonder how many youngins know what a manual choke is, or how to use one correctly.
Not being unkind. There are people my age (75) who don't know.

 

Try running Marvel's in the gas in the fuel tank per instructions. 4 fl. oz per 10 gallons. Compression numbers are a little low but they aren't too bad. Driving and heat cycles along with a solvent will help free up stuck varnished rings. Those plugs are running way rich.

A manifold vacuum test doesn't lie, it will tell you a lot about engine condition and state of tune. A high steady vacuum is what any carburetor calibration and set points are designed around, the idle circuit and transition circuits use this as a signal. If manifold vacuum, ignition, or ignition timing is defective the carburetor will not respond correctly. You know all this stuff already, you'll find the culprit.

 

Also remember that the condition of the battery and starting system will affect your compression numbers. You did your test cold, but your warm numbers might be higher because of more oil on the cylinder walls to help seal the rings, warmed up oil to raise cranking speed, etc. They might not! It might be worth a warm test to see; you might be worrying about nothing as far as engine wear is concerned.

That plug looks like the result of a rich mixture rather than oil fouling to me (but pictures are sometimes hard to read). Modern gas expands a lot in the bowl - might the float be a little high? With old carburetors, you never know what someone's drilled out inside. Everything might look fine, but someone in the past might have tried to play carburetor expert with dubious results.

 

One Tune-Up error in general I've noticed, doesn't really apply here but, everybody always wants to start dinking around with the carburetor very first thing, when the carburetor is (more or less) the very last thing to be adjusted, because everything else will affect carb operation in a big way.

Maybe because it's right up on top front and center and easy to get to? You know, a guy loses his car keys in a dark alley, but the light is better under a street lamp so he'll look there instead.

Engine runs like shit. What to do? How about a "Tune-Up"? First, replace perfectly good OEM ignition parts with some imported crap junk from golly knows whsre. Then it goes something like this:

Tune-Up Manual Pg. 1 Para. 1 : Check Compression

"Hm. I don't have a compression gauge. Skip that."

Tune-Up Manual Pg. 2 Para. 1 : Vacuum Test

"Hm. I don't have a vacuum gauge. Skip that."

Tune-Up Manual Pg. 4 Para. 1 : Ignition Timing

"Hm. I don't have a timing light. Skip that."

Tune-Up Manual Pg. 7 Para. 1 : Voltage

"Hm. I don't have a voltmeter. Skip that."

Hey I know! How about a brand new shiny carburetor! That'll get 'er all fixed up I betcha.

 

Truck64 - I like your tale of often-used diagnostic sequences. As you mentioned, not applicable to this particular thread.

I have long contended that carburetors produced prior to 1930, in general, cause less problems (more reliable???) than their modern counterparts!

WHY?

They are all updraft, difficult to get to, difficult to get off; and it is much easier to solve the actual problem than fool with the carburetor!

Jon

 

Hi Jon,

I apologize for the late reply, we're in the process of putting up a new shop in the backyard and this last week has been crazy. The concrete was finally poured as of yesterday.

I haven't put a tach on it yet but it sounds like she's between 1500-1800 rpm (maybe sooner) when it happens. I'll try to get this info for you this weekend.

Last night a neighbor said that maybe the air bleeds or other small passages might be blocked, causing the transition circuit be be messed up. So I pulled the carb off, tore it apart, and blew the crap out of everything. Put everything back together and the problem is still there. At least now I am now 100% certain that the carb is as clean as a whistle.

After that, I went to O'Reilly auto parts and picked this up. I'll try to get it installed this weekend and operate it as you suggested. Hopefully I can get in the habit of using it so I can start putting some miles on this old girl. I'm hoping that she slowly starts freeing up like you has mentioned.

I haven't heard anything online about blocking the heat cross-over. What is it supposed to accomplish?

That's great that a manual choke helped you out so much. It makes me feel better about moving forward with this. I wish I could get to the bottom as to why exactly this is happening, but like you said, with out pulling the engine part, this will at least get it drivable.

Anywho, thanks for all of your help. I super appreciate it.

-Chris

 

I'm 37 and I just heard about them about a month ago. A buddy of mine was selling a carb at a swap meet and it had a manual choke on it. I asked him what it was and he schooled me on it. Pretty interesting stuff.

-Chris

 

Okay, I'll go ahead and add some MMO to the fuel today. By solvent, do you mean I should add some acetone or something like that to the rings after she's been ran for awhile?

Yeah, I thought they looked super rich as well. I may have to play with the enrichment screws a little more.

You're right, I really need to get a vacuum gauge on there and see what she's doin'. Until I do, I'm kinda beating a dead horse. Right now the contents of my garage are in my living room. my van, and my shed because of the new garage build. I'm trying to get this thing sorted so I can enjoy her this summer, but it's really hard with all my tools scattered all over the place. So far my neighbors have been great in helping me out through all of this.

-Chris

 

Spray starting fluid around the carb and intake, if the idle rises you have a vacuum leak somewhere!

 

The battery is brand new and fully charged, and the starter spins up just fine.

I was always told it was best to do a compression test cold so you could get the true compression numbers. I'm sure they would be higher if the engine was warm, but wouldn't the numbers not really be a true reflection of the engine condition?

I agree, the plugs do look pretty rich. The the carb rebuild kit came with those newer style needle and seat setups. The ones with the rubber tipped needles. When using these, I did have to adjust the float level but I set it exactly like the factory manual suggested. I think everything is fine in that regard. I'll keep playing around the things though, the idle enrichment screws may be set to rich.

-Chris

 

I haven't done this yet, but when I screw the idle enrichment screws all the way in, the car is almost about to die. If I had a vacuum leak, especially a bad one that would be the reason for this issue, I don't believe those screws would respond at all.

I did pinch off the vacuum lines to the brake booster/vacuum tank, and the vacuum pump. The problem was still present after I did this.

 

The Marvel's oil has solvents and penetrating oil in it, designed for just this purpose. Old gasoline and oil and sludge and gum varnish over the years turns into a kind of glue. It won't restore excessive cylinder or ring wear or burnt valves, but it will keep stuff moving that's supposed to be moving. Piston rings, lifters, and help remove carbon from valves. Make sure engine is getting up to normal operating temp, ignition has a good hot spark.

A defective carburetor power circuit will make plugs burn rich like that. Remember with modern unleaded gasoline formulations, if spark plugs look coal black, it's probably approaching the burn limit.

The float height adjustment is just a rough bench setting to get in the ballpark, once carburetor is on the engine the actual fuel height achieved at idle in the carb bowl is what matters. Make sure the pump output pressure isn't excessive, and the needle and seat is doing its job. The vacuum gauge doubles as fuel pump tester, too. Handy dingus.

Have to sneak up on carb tuning, because a defective circuit or maladjustment anywhere along the line will bugger the whole shootin' match downstream. The fuel height +/- a red nether hair in the bowl affects cruise jetting a fair bit, the power circuit (if defective) will confuse matters considerable too, and jetting affects the fuel quantity the power circuit provides on demand too. Just tune everything by the book in order one step at a time and you can't go wrong.

 

Ah, okay. I'll try introducing some MMO to each cylinder when I get a chance. Maybe it'll help out those rings.

By power circuit, is that the accelerator pump?

I don't see any indications that there are any problems with the float circuit, but yeah never know. I haven't checked the fuel pressure yet, I'll add that to the list.

Thank you for all the advice, I'll definitely make it a point to tune everything like it should and go from there.

-Chris

 

Update: Just checked the vacuum at idle. She was sitting around 19 inches of vacuum initially, I then played with the enrichment screws and got her up to 20 inches. I also recorded the issue at hand. Here is the link:





-Chris

 

Think about how long you drive a cold engine vs one that is at operating temp.
That’s why a proper compression test is done on a warmed up engine.

 

No, put it in the gas, in the fuel tank. About 4 oz. per 10 gallons.

 

That's I thought at first but then reread your post and thought you wanted it to soak the rings. Sorry about that. Anywho, I added the MMO to the gas like you suggested.

-Chris

 

I'll try to redo the compression test with a warm engine sometime this weekend. I'll update this thread with the results.

-Chris

 

If an engine has acceptable, passing compression #s when cold, I always figured it would only improve the numbers when fully warmed up, so a "hot" test in that instance would be unnecessary. Could be wrong on that.

The numbers listed for your engine don't look too bad. It is a good candidate for tuning up. It's more important that the compression is close and even across all cylinders, versus the absolute number. About 140 to 150 psi would be typical for an 8 to 1 compression ratio though. Compression #s will likely improve about 10 pounds and even up when it gets some heat cycles, some highway time.

Thing is with doing a compression test hot, is the engine is ... hot, and it's a pain in the ass. One thing somebody suggested is to loosen the spark plugs when engine is cold and just snug them down, that way they aren't a bear to remove when hot. Work quick, make sure battery is fully charged, remove all the spark plugs first, and block throttle wide open.

You could also maybe check for a sloppy timing chain set. With the distributor cap removed rotate the engine at the damper bolt counter-clockwise two full revolutions and stop.

See where the timing pointer is on the damper and maybe mark it with a grease pencil. Now very slowly and carefully turn the damper clockwise while at the same time watching the distributor rotor, as soon as it does, stop turning the damper. Ideally the rotor will start moving just as soon as the crankshaft does, this means there's no slop or wear in the timing chain set. 3 to 4 degrees movement before rotor starts to turn is probably OK. More than that, it is getting sloppy. This causes late valve timing, a different animal than late ignition timing. Causes sluggish engine operation down low, lower compression, and poor cold weather starting.

 

See, that's what I figured and was always told. Thanks for clearing that up for me.

Yeah, I was most surprised that they were all relatively even. I found a piece of paper in the glove box that had some pretty scary compression numbers written on it. They are a little low but I'm just stoked that they aren't like the readings on that paper.

The timing chain could very well be an issue. I do hear what sounds like a really lite metallic sound coming from the front of the engine during idle. When I get the garage put back together, I'll do the test that you outlined and see what I can find.

Thank you,

-Chris

 

UPDATE:

I installed a manual choke yesterday like carbking suggested so I can start driving this old girl until I figure out what's going on. When the lean surging happens during cruise, the only way she's happy is when the choke is FULLY CLOSED. We were cruising about 40 mph (don't know RPM) and she was happy as a clam.

Obviously something is up. That means she must be getting air from somewhere right? How is it possible that she has a vacuum leak that big only during a certain RPM range?

At idle there are no signs of any vacuum leaks. She idles at a nice low rpm and the enrichment screws will get her to die if turned in all the way.

Anyone have any thoughts?

-Chris

 

Ordinarily if everything is otherwise straight a "lean surge" or misfire on steady cruise flat ground would be due to jetting. Too small.

But somebody had to go out of their way a little bit to make that happen. Most carburetors will typically run a bit or well on the rich side of things.