ClemSparks
ClemSparks UltimaDork
8/11/19 3:08 p.m.

[Edit:  I think I have this kind of figured out...at least for now.  I REALLY appreciate all the discussion]

 

I got this '81 Fairmont the other day and I'm trying to get it to run right.

 

 

The carburetor it had on it felt like it was “loading up” or something at stops and would ultimately die unless you did some two-foot throttle/brake action to keep it running. There was a “spare” carburetor in the trunk when I got the car. It's slightly different than what was on the car, but it appears to be mostly the same as what's on my '80 Fairmont Wagon and it looked better than the one on the car...which clearly had some coffee-can-sourced screws and other ham-fistery going on.

 

This is a Holley 1946 one barrel carburetor.

 

So, I ordered up an NOS eBay brand carburetor kit (Pronto brand, actually) and yesterday I cleaned everything up in my ultrasonic cleaner, blasted out the passages with brake parts cleaner, slapped it all back together and bolted it on the 200 inline 6 to see how I did.

 

It's better. But I do have a problem: A major bog off idle with light application of throttle. This problem was not happening with the old carburetor.

 

I hooked up a vacuum gauge to the intake manifold vacuum distribution fitting and adjusted the idle mixture screw until I got the best vacuum (about 18” hg). But I noticed that it will die immediately with light throttle application. If you step on the throttle hard (under load or in neutral) the bog is not evident. But if you're just trying to leave from a stop in “I have a passenger in the car” driving style...it dies. I tried some different idle mixture and throttle stop settings but so far I cannot get rid of this bog on light throttle.

 

I'm no stranger to carburetors...and this seems like it should be pretty simple. But I thought maybe by working through it here with a few other knowledgeable folks, I could get it running right.

 

Some things I've tried or verified so far:

Timing seems correct at more-or-less 10 degrees BTDC (verified with timing light).

The idle mixture screw is around 2-2 ½ turns out to get the highest idle...seems reasonable.

The accelerator pump appears to be functioning correctly. It squirts fuel when I apply throttle.

I can crank the idle screw all the way closed and the engine doesn't die...but it BARELY keeps running. This could be indicative of a problem.

When you're cruising along at higher-than-idle RPM, there is no bog, just instant throttle response.

The bog is present regardless if the car is cold or at operating temperature.

The electric choke seems to be operating as it should.

 

Things that I'm not sure about:

Float level. I didn't change/verify/set it when I put it together (I just slapped it together the same as it came apart) and I'm not sure if that could contribute to this problem.

Vacuum Advance on distributor. I've hooked it to the same port on the carburetor that is is at on the '80 Fairmont with the same setup that runs just fine. This port doesn't seem to have vacuum at idle. I've also tried hooking it to the manifold vacuum port. The problem doesn't seem to go away or change much...it might be a little different but it's still there and just as bad.

Hot Idle Compensation: This carburetor was missing what I've learned is the “hot idle compensator valve” so I stole the one off the carburetor that was on the car. It seemed like it had been tweaked a bit...not sure if that has anything to do with this. It is doing it both hot and cold, so who knows. I might try locking this compensator thing down to see if anything changes.

 

Am I missing anything? Is it just that I didn't get a circuit cleaned out somewhere in there? Power valve, maybe? It has a thing in it that the instructions call a power valve, but it's not like the standard power valve on a 4 barrel holley.

 

Discussion appreciated if you have experience with these carburetors specifically or carburetors from this era in general.

 

Ultimately, I'd like to trim this down to the bare essentials and get rid of a mile or two of vacuum hose if possible ;).

ShawnG
ShawnG PowerDork
8/11/19 3:21 p.m.

The bogging / stumbling off idle might be a vacuum leak somewhere.

You said the accel pump is giving a good, strong squirt so it's ruled that out.

Did the base gasket have any extra slots or holes in it? Did you match it to the carb base and manifold to make sure everything was lined up?

All unused vacuum ports blocked off or plugged?

Maybe spray some carb cleaner around any areas where air my leak in and see if the idle changes.

ClemSparks
ClemSparks UltimaDork
8/11/19 3:27 p.m.

THANKS!

 

I did get out the propane torch (unlit) and pass it around the base of the carburetor to check for vacuum leaks there.  No change in idle when I did that.  The base gasket on this thing is stupid-simple so I'm fairly confident that's not the source of the leak. 

I will say...when you deliberately create a vacuum leak (pull a hose or cap off the manifold fitting) it's QUITE obvious.  That has me thinking that I don't have a substantial vacuum leak.  But I'd LOVE to find that I do and the fix is that simple.   

I will try to cap off EVERYTHING but the brake booster hose and Vacuum Advance and see if it changes anything.

 

One thing I meant to mention in the opening post (I may go back and edit) is that it has a massive exhaust leak between the head and the manifold at cylinder #1 (maybe #2 also).  This is something I'll get around to fixing when I'm feeling like some misery.  I don't imagine it has any bearing on this problem but I wanted to mention it just in case.

Curtis
Curtis UltimaDork
8/11/19 3:28 p.m.

First thing to check is that mile or two of vacuum lines for leaks.

Second thing I would check is the throttle shaft bore for play.  The shaft eventually wears out the bore causing a vacuum leak that sometimes only shows up when the cable pulls the throttle.  This was the issue on Duke's old 67 LeMans.  I pulled it apart to put the fixer bushing in the bore only to find out that the bushing fell right through without even having to ream it.  The fix was my buddy who had a 2GC sitting around and gave me a different throttle plate.

The factory vacuum for the dizzy is probably a ported source.  If you have it hooked to manifold, it would give you tons of lovely advance at idle, then retard timing significantly when you touch the throttle.

Did you verify that the throttle plate is not uncovering the ported vac hole?  It's an easy thing to do with a carbed car... you set timing, idle speed, idle mix, etc, only to find out that the way you got that perfect idle was to accidentally use not enough physical advance and too much idle speed adjustment.  You can do darn near anything you want with ignition advance at idle to test things.  Grab the dizzy and advance it a bunch and back down the idle screw.  Keep doing that (advance and lower idle or retard and raise idle) until you get the right idle at the right timing.

Curtis
Curtis UltimaDork
8/11/19 3:34 p.m.

By the way, that blue color is the exact color I painted my old boat which now belongs to my nephew

Behold, the Blue Goose:

ClemSparks
ClemSparks UltimaDork
8/11/19 3:35 p.m.

Thanks Curtis.

The throttle shaft felt nice and tight when I had it apart.

I really didn't have to crank the throttle stop screw to get a good idle speed.  I'm pretty sure the idle circuit is still being utilized.  This was one of my first thoughts (I was idling on the main circuit and this was causing issues.  It's still possible but the throttle shaft really isn't open very far at all, I don't think.  I'll double check this.

I'm going out to the car to try to fully eliminate vacuum leaks (outside of the carburetor itself) as a possible cause...

ShawnG
ShawnG PowerDork
8/11/19 3:55 p.m.

Another thought.

A lot of those kits include multiple gaskets for the body / air horn joint that can look very similar but cause a leak if they're not exact.

Don't match them up to the one that you took out because it could be wrong too, that carburetor may have been taken off for a reason.

Always lay the gasket on the parts that it seals, do both sides. Check to make sure all the ports line up and there is nothing going to "outside" or ports being blocked that shouldn't be.

I've found lots of previous owner repairs on carburetors that involved "just put a kit in it" that actually made problems worse.

Knurled.
Knurled. MegaDork
8/11/19 4:08 p.m.

Does the vacuum advance in the distributor work?

 

How much of the transfer slot is visible above the throttle plate when at idle?

Dusterbd13-michael
Dusterbd13-michael MegaDork
8/11/19 4:12 p.m.

I had a 300ci ford six that cracked the intake manifold.  The crack opened when the manifold got hot, killing the engine via vacuum leak. Wouldn't do it cold.

Maybe a similar failure?

ClemSparks
ClemSparks UltimaDork
8/11/19 4:17 p.m.

I'll take the top off the carb to verify.  I was moving quick but did lay the gasket (there was only one in this kit) on and it seemed like all was well.  I'll look again.

 

I went out just now and capped off every vacuum port EXCEPT the line to the brake booster and the Vacuum Advance.  It was pulling around 16-17 in-hg.   As before...when I deliberately created a vacuum leak (pulled a cap off) it was obvious...the idle quality went south.

 

It still bothers me that I can CLOSE the idle mixture screw and it will still idle.  It idles about as slow as possible without shutting off...but it will start right back up and idle there.  Seems like most folks think this means I'm either NOT running on the true idle circuit or it's getting fuel from somewhere else (power valve is a usual suspect).

 

I'm trying to wrap my head around Curtis'ses instructions for finding a natural harmony with the base timing, idle mixture, and idle throttle plate position.  Curtis, if you can expand on that a little, I'll give it a whirl.

 

I read an article by The Carburetor Shop that says a lot of these old carburetors need a throttle plate opening of about  0.020" and then set the itle mixture from there.  Can anyone confirm that.  As it sits, if I look down the bore of my carburetor I can't really SEE that the throttle plate is open at all...but I know it is a little bit because I can feel the throttle arm move and the idle raise when I turn the throttle arm stop.

Knurled.
Knurled. MegaDork
8/11/19 4:23 p.m.

In reply to ClemSparks :

Is your idle screw a fuel controlling screw or an air bleed controlling screw?   It sounds like an air bleed controlling screw.  That makes it a little more wonky to tune up.  It would, however, make the Carb Shop article make sense, as you are setting the idle speed with the screw, not the throttle position.

 

If the throttle is open too far at idle, then the transfer slot won't work properly and it'll have a lovely off idle stumble/bog.  Thus my question about the transfer slot.  (If it has one!)

Curtis
Curtis UltimaDork
8/11/19 7:42 p.m.

I'm with Knurled.  That screw is likely an air bleed.  Older Carter carbs did this too.

Clem, you're obviously knowledgeable on all of this, so forgive me if this sounds elementary.  Many times folks get an engine running and have trouble getting the timing/idle speed nailed down.  Advancing the timing raises the idle, but depending on the vacuum source, raising the idle advances or retards the timing.  The go-to solution when you start an assembly is to raise the idle to keep it running so you can set things.  If you raise the idle, you uncover the vacuum slot (which in a ported-vac system abnormally advances the dizzy, or in a manifold vacuum abnormally retards the dizzy.)

From that tune, it's a difficult thing to get right.  What I was discussing before is that idle timing is pretty inconsequential.  You could alter it from 2 degrees to 30 degrees advance and not hurt a thing.  My suggestion is to add advance first.  If you get kickback on the starter, you've gone too far.  Just put a bunch of initial into the timing.  If you start with too much timing and back it off, it's nearly always a shoe-in that you'll nail it.  If you start with too much idle and retard the timing, you run the risk of getting the numbers right but still having the vacuum port uncovered because you'll get pretty numbers before you reach the actual setting you need.

The typical downfall with this is because people read that they need 9 degrees initial timing and they're afraid to get it too far off.  They start conservative and advance a little bit until the engine runs.  The "X degrees of initial" is only a benchmark for the factory advance curve.  The important part is how it acts at high loads.  You won't damage anything by getting too much advance at idle.

Newbie way:  try to slowly and carefully sneak up on X degrees initial until it runs and then set idle.

Pro way:  Advance the berkeley out of it.  You might get the #6 cylinder firing while the intake valve is open and the backfire will make your neighbors call the cops, but it won't hurt a thing.  The secret is to have too much advance and too little throttle.  Back off the advance and then open the throttle.

Bench-set the idle to spec or a little bit lower.  Guess on the timing and advance a wee bit from there.  Much easier to start with too much timing and too little idle.  Sneak the timing down

iceracer
iceracer UltimaDork
8/11/19 7:46 p.m.

In reply to ClemSparks :

Vacuum seems low

ClemSparks
ClemSparks UltimaDork
8/11/19 8:06 p.m.

Well.

I took the carburetor off to check on stuff and answer some of the questions you all asked.

I have some photos I can add but...

When I put it back on (without knowingly making any changes) it runs fantastically with no bog.  At least on the brief driveway testing I did.  More testing to come but hopefully it will remain "fixed".

Obviously something was amis.  I don't know what it was (Didn't see anything obvious) but evidently it's more righter now.

sergio
sergio Reader
8/11/19 8:07 p.m.

I wonder if the exhaust leak has caused the intake runner gasket next to be burned out causing a vacuum leak.  

Knurled.
Knurled. MegaDork
8/11/19 8:13 p.m.

In reply to sergio :

200s don't have intake gaskets, do they?  I thought all the small sixes (sold in the US anyway) had cast in place intake manifolds.

ClemSparks
ClemSparks UltimaDork
8/11/19 8:14 p.m.
Curtis said:

By the way, that blue color is the exact color I painted my old boat which now belongs to my nephew

Behold, the Blue Goose:

Cool boat!  Now that I think of it, we had a Sweet 16 Sailboat that was approximately this color.

This is the 3rd Ford (that I can remember) from the early '80s that I've owned in this color.  My first was an '80 mustang in about 1992.  Then an '84 F350 circa 2008.

I wouldn't seek out this color (on a car/truck...it looks great on the boat) but it's just kind of nostalgic for me by now. 

I

ClemSparks
ClemSparks UltimaDork
8/11/19 8:23 p.m.
Curtis said:

I'm with Knurled.  That screw is likely an air bleed.  Older Carter carbs did this too.

Clem, you're obviously knowledgeable on all of this, so forgive me if this sounds elementary.  Many times folks get an engine running and have trouble getting the timing/idle speed nailed down.  Advancing the timing raises the idle, but depending on the vacuum source, raising the idle advances or retards the timing.  The go-to solution when you start an assembly is to raise the idle to keep it running so you can set things.  If you raise the idle, you uncover the vacuum slot (which in a ported-vac system abnormally advances the dizzy, or in a manifold vacuum abnormally retards the dizzy.)

From that tune, it's a difficult thing to get right.  What I was discussing before is that idle timing is pretty inconsequential.  You could alter it from 2 degrees to 30 degrees advance and not hurt a thing.  My suggestion is to add advance first.  If you get kickback on the starter, you've gone too far.  Just put a bunch of initial into the timing.  If you start with too much timing and back it off, it's nearly always a shoe-in that you'll nail it.  If you start with too much idle and retard the timing, you run the risk of getting the numbers right but still having the vacuum port uncovered because you'll get pretty numbers before you reach the actual setting you need.

The typical downfall with this is because people read that they need 9 degrees initial timing and they're afraid to get it too far off.  They start conservative and advance a little bit until the engine runs.  The "X degrees of initial" is only a benchmark for the factory advance curve.  The important part is how it acts at high loads.  You won't damage anything by getting too much advance at idle.

Newbie way:  try to slowly and carefully sneak up on X degrees initial until it runs and then set idle.

Pro way:  Advance the berkeley out of it.  You might get the #6 cylinder firing while the intake valve is open and the backfire will make your neighbors call the cops, but it won't hurt a thing.  The secret is to have too much advance and too little throttle.  Back off the advance and then open the throttle.

Bench-set the idle to spec or a little bit lower.  Guess on the timing and advance a wee bit from there.  Much easier to start with too much timing and too little idle.  Sneak the timing down

THANKS a bunch!  That sounds good to me.

I've been screwing with carburetors my whole life but I'm no expert.  I just rebuild one every so many years and kind of forget the basics in between times.  Before I posted here I tried to rule out all the obvious/easy stuff.

I haven't ever heard the "Add timing until the neighbors call homeland security" method but it makes sense and I like it!

Again, I really appreciate your taking the time to spell that out.  I'm sure I'm not the only one who will benefit from it.

ClemSparks
ClemSparks UltimaDork
8/11/19 8:25 p.m.

In reply to iceracer :

I should throw the gauge back on it to see if it's higher now that it's running better.

I think it's safe to say that low vacuum is not caused by the massive cam in this beast.

ClemSparks
ClemSparks UltimaDork
8/11/19 8:30 p.m.
Knurled. said:

In reply to sergio :

200s don't have intake gaskets, do they?  I thought all the small sixes (sold in the US anyway) had cast in place intake manifolds.

This is correct.  The intake is a feature cast integrally with the head.  If not for that, Sergio's thought would have been something to check out.

dropstep
dropstep UltraDork
8/11/19 9:03 p.m.

Sounds alot like what I was going through on mine this spring when I got it out. Mine ended up being a bad choke coil. Sounds like yours might have been a different issue though

ShawnG
ShawnG PowerDork
8/11/19 10:44 p.m.

One trick I use when I suspect it's not actually idling on the idle circuit:

Take a flashlight and look down the throat when it's at idle. If you see fuel dripping from the booster venturi, your throttle plate is open too far and you're coming off of the idle circuit.

If you can't close the throttle enough to get it to stop pulling fuel from the booster, double-check your timing. Excessively retarded timing can make you need to open the throttle more to get a good idle.

Double check that the damper ring on the harmonic balancer hasn't slipped. If it has slipped, your timing marks will be out of whack.

At the age of the car, the balancer may be getting a bit rotten.

Timing issues can seem a lot like fuel problems.

Knurled.
Knurled. MegaDork
8/12/19 2:21 a.m.

I wonder if something was mucked up in the float/N&S setup, causing the fuel level in the bowl to be too low, and taking the carb off and inverting it and stuff made it un-muck itself.

 

The Nikki carbs on RX-7s are somewhat infamous for the opposite effect.  Take them apart, or even just take them off and put them back on again, and there's a good chance that one of the needles will stick open and turn the carb into a fuel fountain.  The "fix" is a Fonzie style well-placed thump with a hammer to jog everything back into place.

Curtis
Curtis UltimaDork
8/12/19 7:34 a.m.
ClemSparks said:
Curtis said:

By the way, that blue color is the exact color I painted my old boat which now belongs to my nephew

Behold, the Blue Goose:

 

Cool boat!  Now that I think of it, we had a Sweet 16 Sailboat that was approximately this color.

This is the 3rd Ford (that I can remember) from the early '80s that I've owned in this color.  My first was an '80 mustang in about 1992.  Then an '84 F350 circa 2008.

I wouldn't seek out this color (on a car/truck...it looks great on the boat) but it's just kind of nostalgic for me by now. 

I

It's a 58 or 59 Montgomery Ward Sea King.  It was poop brown when I bought it and had a 63 Evinrude 10hp on it.  I redid the whole thing and put a 25hp Merc on it.  Fun boat, but I passed it on to my nephew.

Curtis
Curtis UltimaDork
8/12/19 7:37 a.m.
ClemSparks said:

 

I haven't ever heard the "Add timing until the neighbors call homeland security" method but it makes sense and I like it!

Again, I really appreciate your taking the time to spell that out.  I'm sure I'm not the only one who will benefit from it.

You're welcome.  The first time I did the "homeland security" method was on a Pontiac 389.  I advanced so far that the intake valve was still open on #8 and it ignitied the charge in the intake.  It sounded like a rifle going off and shredded the insulation under the hood.

I'm not suggesting ALWAYS going that far, but I just use that example to point out that idle timing is inconsequential for idling purposes.  You need to get it right so that it works properly in the rest of the operating range, but for setting up idle and timing it won't hurt to be too advanced.

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