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11/19/2020 6:56 AM  #26


Re: Autolite Tune Up

Bullet Bob wrote:

TKOPerformance wrote:

Adjusting the float(s) won't make the carb run less rich

Well, that shoots down what I always thought.  I was of the opinion that the float level was designed into a carburetor to establish the desired hydro static pressure on the fluid under the spray devices located in the low pressure area of the venturi.  The lower the hydro static pressure...low float level...the less fuel will be delivered for a given volume of air passing through the venturi.  The exact opposite is true for high float level.  I'm pretty sure that if the level is high enough for fuel to be running out of the bowl vent there will  be excess fuel slobbering into the venturi with little or no air flow through the pot.  Yes, the jets control the volume of fuel delivered but they are calculated to do so at a calculated volume of air flowing through the venturi.  Which, I believe is why a pot goes lean at high altitude.  The actual mass of the air entering the engine is less and and the hydo static pressure on the fuel is less so a given jet delivers less fuel.

I had a 283 bowtie in my 55 F100 years ago and it started getting hot anytime I pulled the slightest hill or worked it a bit.  Never missed or stumbled...just started heating.  Running flat was no problem.  It had two fuel tanks with a manual change-over and I discovered that all five pieces of neoprene connecting it all together were dry and had little splits.  The dang thing was sucking just enough air that it couldn't keep the float bowl full when it started working.  So...it went lean and heated.   Or at least that's what I reasoned.

So that's what I always thought but I'll certainly listen to a better explanation if I'm just full of the old dirty brown stuff.

BB1

I get that its a small orifice, but the difference in fuel volume between a nearly empty float bowl an a nearly full one doesn't seem enough to create a meaningful pressure differential between the two states.  The float bowl exists to provide an unpresurized  reservoir of fuel.  Without it you would be running fuel pump pressure into the carb and there would be no way to control fueling.  The reservoir needs to be big enough to have enough fuel and allow it to refill when the engine is running wide open and burning a ton of fuel.  The engine uses very little fuel at idle, but at WOT think about how quick that bowl runs dry if you've ever turned off the fuel and run an engine to run it out of gas it takes a couple seconds at most at WOT.  Also, if there was such a pressure differential between full and nearly empty the AF ratio would be all over the place based on where the float level was.  It would be impossible to figure that out dynamically. 

You get rich at altitude because the air is less dense so there's less oxygen in the atmosphere.  When a gas engine gets rich power takes a nose dive (remember "lean is mean").  This is why piston aircraft have employed superchargers to compensate for the vast difference in oxygen levels the higher in altitude they go.  You get lean when its cold outside because the air is denser with more oxygen. 

Sucking air into the system from a leak is either causing it to vapor lock, or run out of fuel because the reservoir isn't staying full.  I've had this happen on a Diesel where there was obviously no carb, float bowl, etc.  A Diesel will run on AF ratios from 100:1 to maybe as low as 6:1, so while you wouldn't be making great power the leaner you got it would still run, yet I've had one run out of fuel and stall due to air leaks in the fuel system, which did not leak fuel out; only sucked air in. 
 

 

11/19/2020 7:48 AM  #27


Re: Autolite Tune Up

Okay, I'll stand somewhat corrected.  Also, I have to apologize 'cause I stated "lean" at altitude and that's certainly bass-akwards.  If I had caught that error in my thinking I probably would have scrapped the whole post.
Good explanation, Tom. 
But one more time...that old chevy wasn't running out of fuel, it was just getting hot.  First time it happened I was running slow up a long trail up to a lake.  Running just off idle but pulling a bit.  Never stumbled, just got hot because the fuel pump could not keep the bowl at design level.
I'm gonna have to do more research but I do understand what you're saying and pretty much agree.

PS:  Not that they know everything but Wickipedia says:  Carburettors are provided with a float chamber to provide a constant hydrostatic head of fuel above the carburettor's metering jets, thus a constant pressure. The float chamber itself does not vary the pressure according to demand, but it does vary the supply flowrate with demand, to keep this pressure constant.

BB1

Last edited by Bullet Bob (11/19/2020 8:01 AM)


"you get what you pay for, good work isn't cheap, and there are NO free lunches...PERIOD!"
 

11/19/2020 5:29 PM  #28


Re: Autolite Tune Up

Well sure, the fuel in the bowl is above the jets, so gravity is acting upon the fuel.  The pressure in the float bowl is atmospheric pressure though, because the bowl is vented to the atmosphere.  I would argue that the float bowl does not vary the flowrate upon demand; the air being drawn through the carburetor does that.  As the engine accelerates more air enters in a given time period creating a greater depression through the carb, thus increasing fuel flow out of the float bowl.  The float bowl itself has nothing to do with that increase in flow; its contents are being acted upon by an external force.  The float bowl simply ensures that there is enough fuel to supply the increased demand. 

I find that Wikipedia at times when it comes to engineering things is either written by someone for whom English clearly is not their first language, or who simply lack a good fundamental understanding of their native tongue.  I suppose for some engineers when you are used to writing using symbols and numbers that sentences can at times be a challenge.  I can tell you for example that the term hydrostatic head is simply misused in this context. 

 

11/19/2020 5:33 PM  #29


Re: Autolite Tune Up

TKOPerformance wrote:

  I can tell you for example that the term hydrostatic head is simply misused in this context. 

Okay.

BB1
 


"you get what you pay for, good work isn't cheap, and there are NO free lunches...PERIOD!"
 

11/20/2020 3:09 AM  #30


Re: Autolite Tune Up

I am curious on how much life you can get out of a pcv valve. I still need to check mine, but maybe this is something I need to just replace?
 


1964-1/2 D Code Coupe - 289 V8, 4 Speed Toploader, 3.00 ratio rear, Autolite 4100 Carb, 15" tires, Pertronix ignition
     Thread Starter
 

11/20/2020 6:22 AM  #31


Re: Autolite Tune Up

It's fairly typical to just replace them, often at tune up time because they are typically pretty inexpensive.  You can typically tell if they are stuck by rattling them around and if you hear the ball rattle you know they are not stuck.  This doesn't however mean that the spring in them has the correct tension.  One issue guys have found over the years is that Ford used to list dozens of PCV valves for a variety of applications.  The aftermarket has now shrunk this down to only a couple.  Also, when modifying an engine the criteria for proper PCV valve function changes and there is no way to correct it with a stock PCV valve.  There is a company that sells adjustable PCVs.  Some years back I set up a group buy from them for forum members.  The valves are fairly expensive, but they are also a lifetime purchase as they are adjustable and rebuildable.  The group buy dropped the price considerably, but that's unfortunately long gone.  Information about them can be found here:

http://mewagner.com/

 

2/03/2021 7:16 PM  #32


Re: Autolite Tune Up

Today after being out and about in the car, I detected a gas smell and when I returned home, I popped the hood and could see that the carburetor was weeping out the top once again. It is slight, but enough for me to get my finger damp when I wipe the gas up.
I have had the Autolite 4100 on the car for about 12 years now, so I am wondering if it is starting to show signs of needing a rebuild? Car runs great, but I think it still runs rich. My mpg seems to be down around 14 too and I am sure that is not the best for a relatively stock 289.
With Pony Carbs no longer around, I am considering putting the Autolite 4100 in a sealed bag on a shelf and purchasing the Summit equivalent. Something around 480cfm. Summit sells their carburetors for just over $300, so that would be cheaper than getting mine rebuilt anyway.
I am at a bit of a crossroad here and wondered what you good folk would do in this situation...


1964-1/2 D Code Coupe - 289 V8, 4 Speed Toploader, 3.00 ratio rear, Autolite 4100 Carb, 15" tires, Pertronix ignition
     Thread Starter
 

2/04/2021 6:28 AM  #33


Re: Autolite Tune Up

I kept my original Autolite and manifold, but run an Edlebrock Performer and Edelbrock 1403 500cfm carb on the engine.  Personally I prefer the Edelbrocks because they are super easy to tune and run fairly well out of the box.  On a stockish 289 you will need to lean then out just a bit. 

I have heard good things about the Summit carbs.  One thing you should definitely do if you go that way is to disassemble the carb and make sure there is no junk in it.  I've read several stories about people installing them only to find they got clogged up in short order because there was trash in the float bowls. 

 

2/04/2021 6:51 AM  #34


Re: Autolite Tune Up

Is it nuts to just abandon the the Autolite 4100? Is 12 years a fair run out of the carburettor? What is going on for it to be weeping? It has to be the floats, right?
The Summit carburettor is pretty cheap, so when I compare that to the cost of trying to sort out the Autolite...
Its a bummer really. It has been a really good carburettor.


1964-1/2 D Code Coupe - 289 V8, 4 Speed Toploader, 3.00 ratio rear, Autolite 4100 Carb, 15" tires, Pertronix ignition
     Thread Starter
 

2/04/2021 1:08 PM  #35


Re: Autolite Tune Up

Toploader wrote:

Is it nuts to just abandon the the Autolite 4100? Is 12 years a fair run out of the carburettor? What is going on for it to be weeping? It has to be the floats, right?
The Summit carburettor is pretty cheap, so when I compare that to the cost of trying to sort out the Autolite...
Its a bummer really. It has been a really good carburettor.

Why not go through it yourself??
If I can do it (and thousands of other car guys) rebuild it yourself and save a lot of $$$ and learn about what makes it work!
If you crapit up.so what..... you're planning to buy a replacement anyhow!!
Rebuild kits should be pretty cheap......HEY.its wintertime!!   Pull it out and play-with-it!
6sally6
 


Get busy Liv'in or get busy Die'n....Host of the 2020 Bash at the Beach/The only Bash that got cancelled  )8
 

2/04/2021 2:40 PM  #36


Re: Autolite Tune Up

The primary reason I went away from the Autolite wasn't reliability, power, or a problem; it was that I wanted to be able to tune it easily and effectively.  If you're planning on keeping the engine the way it is then that's not a concern and I'd suggest trying to rebuild it too.  I will say that the float in mine needed to be set much lower than the rebuild kit instructions stated.  Pony Carbs knew that, and when I had an issue I went back to their setting and eliminated the issue I was having.  Its a shame they are gone; they were a real brain trust for the Autolite carbs. 

 

2/04/2021 4:08 PM  #37


Re: Autolite Tune Up

I'm big on having the car being reliable, with decent performance. It will never be a hulking great powerhouse, but I do plan to fit a dual plane intake manifold at some stage. If I get a new carburettor, I would probably shell out and get a new manifold at the same time (maybe).
I've done the carb rebuild and tuning in the garage thing over the past 25 years, but in the end I came to the decision that its best to have it tuned properly by someone with the correct instruments/sensors.
I love the Autolite, but purchasing a replacement is like twice to three time the cost of one of those Summit carburettors. I think I'm convinced on the Summit carburettors. They seem to get a lot of good reviews and are apparently based off the Autolite design, with a few modifications.
My Autolite is running great, no doubt about it. BUT... It smells rich, gas is weeping and the mpg is not what it should be. Maybe I should take the top off the Autolite myself and reset the floats? Who has the Pony Carbs float settings?


1964-1/2 D Code Coupe - 289 V8, 4 Speed Toploader, 3.00 ratio rear, Autolite 4100 Carb, 15" tires, Pertronix ignition
     Thread Starter
 

2/04/2021 5:36 PM  #38


Re: Autolite Tune Up

The number of people whop can successfully tune a carb at this point is so small that you are probably better off doing it yourself.  The last vehicle that left the factory with a carb was built before most of the guys working on cars now were born.  Everything is EFI and if they can't read a code about it they're often lost.  Even the specialty shops are drying up.  My neighbor works on most everyone's classics (he's a professional mechanic) because no one else can tune them properly, and he's at least 10 years older than I am. 

I don't see the float setting coming out of adjustment.  What might have happened is that the float has a hole in it and isn't floating properly.  This allows the bowl to be overfilled and weep out the bowl vent.  When I rebuilt my Autolite years ago I followed the float setting instructions in the rebuild kit and it puked gas out the vent.  I had to raise the float level a fair amount from where Pony had set it when the rebuilt it many years before to get to the height spec'd in the instructions.  Once it puked I knew I had to go back to the way it was and was able to get it right with only two tries.  My advice is don't bend of adjust anything, just replace the old parts with the parts in the kit and it should be fine. 

 

2/04/2021 9:49 PM  #39


Re: Autolite Tune Up

As best I know, the floats are floating ok. I think somehow the setting changed. It weeps around the top gasket.
Is it possible to get the Pony Carbs float settings?


1964-1/2 D Code Coupe - 289 V8, 4 Speed Toploader, 3.00 ratio rear, Autolite 4100 Carb, 15" tires, Pertronix ignition
     Thread Starter
 

2/05/2021 6:32 AM  #40


Re: Autolite Tune Up

The float setting has to be changed by bending a tab.  There's simply no way that happened inside the carb.  Another possibility is that the needle and seat for the float bowl isn't sealing 100%.  There could just be some junk caught up in it.  It could be the needle has a rubber tip that has degraded over time.

I'd love to tell you the height I set my float, but I did this 6-7 years ago by trial and error.

If its weeping around the top gasket it may just be that the gasket is bad.  I also remember seeing something about a problem particular to the Autolites where there was too much distance between two of the top cover screws.  The solution was to add an additional sliver of gasket material in that area to stop the weeping. 

 

2/05/2021 8:08 PM  #41


Re: Autolite Tune Up

What's the average life out of a carburettor these days, before you need to rebuild or replace?
Mine is about 12 years and has about 45,000 miles.
I just rechecked my mpg and it is now down to around 13.7mpg around town. It's getting worse.

Last edited by Toploader (2/05/2021 8:17 PM)


1964-1/2 D Code Coupe - 289 V8, 4 Speed Toploader, 3.00 ratio rear, Autolite 4100 Carb, 15" tires, Pertronix ignition
     Thread Starter
 

2/06/2021 7:15 AM  #42


Re: Autolite Tune Up

First, I wouldn't just assume the carb is the cause of your dip in mileage.  If the area you live in has winter blended fuels they tend to have more alcohol (ethanol) in them, to reduce emissions in colder weather, but alcohol isn't as good a fuel as gasoline.  You need 20% more alcohol to get the A/F ratio correct to run an engine.  That's not to say you're going to use 20% more fuel, because you aren't running straight alcohol.  But if stoich A/F for straight gasoline is 14.7:1, the for a 10% alcohol blend its 14.4:1.  Increase that to 15% and its 14.3:1. 

Second, how old is the rest of the tune up?  When was the last time you changed the plugs, wires, cap and rotor, etc.?  I would take a look at those components (points and condenser too if you still have them).  There are reasons why an engine suddenly runs rich other than the carb being off. 

Third, how long a carb lasts depends mostly on how its used.  If the vehicle is driven frequently its going to last a lot longer, especially with the ethanol in the fuel today.  The problem with ethanol is that like any alcohol its hygroscopic (it absorbs water).  It also doesn't stay blended into the gasoline in a vehicle that sits.  Eventually the alcohol and water settle to the bottom of the tank (or float bowl).  Water can create corrosion, and this is how gunk and trash can mysteriously appear in what we see as a sealed system (its not really sealed, float bowls are vented to the atmosphere, the gas tank is vented or holds some measure of air even when sealed).  If the car is going to sit for prolonged periods you should add something to the fuel like Startron and run it through the system so it can protect everything.  Some guys even use regular old two stroke oil, but I would caution to use only non synthetic as the synthetic stuff eventually separates from the fuel.  Adding a pint to a full tank of fuel isn't going to be enough to make it smoke or affect power or mileage, but it will offer protection. 

 

2/06/2021 10:10 PM  #43


Re: Autolite Tune Up

Carburettor was tuned maybe three months ago...
Plugs are maybe a year or so old. Plug gaps all set.
Plug leads were replaced at the same time as plugs.
Ignition system is Petronix. Cap and rotor not that old. Coil is not that old either.
Car seems to run ok... Mpg is getting worse though and it smell rich, even after tune up. 12 years and maybe 40,000 miles. Maybe its showing signs of wear?


1964-1/2 D Code Coupe - 289 V8, 4 Speed Toploader, 3.00 ratio rear, Autolite 4100 Carb, 15" tires, Pertronix ignition
     Thread Starter
 

2/08/2021 2:25 AM  #44


Re: Autolite Tune Up

Maybe my Autolite could be jetted down to the next jet size? I remember asking Jon (at Pony Carbs) this once and I think he said it could be maybe, but I don't know what jet sizes it should be running?
 


1964-1/2 D Code Coupe - 289 V8, 4 Speed Toploader, 3.00 ratio rear, Autolite 4100 Carb, 15" tires, Pertronix ignition
     Thread Starter
 

2/08/2021 6:17 AM  #45


Re: Autolite Tune Up

Again, the issue I would say that if the jets were right before why all of the sudden are they too big?

If the ignition system is solid I would say a carb rebuild isn't going to hurt anything.  I would look at the oil.  Check color and see if it smells like fuel.  If that seems fine I'd go ahead and rebuild the carb.  If the oil has a fuel smell I'd do a compression test on every cylinder and see what they look like. 

Last edited by TKOPerformance (2/17/2021 10:09 AM)

 

2/09/2021 5:17 AM  #46


Re: Autolite Tune Up

Maybe it's just a case of 12 years of this crap fuel they give us to use has taken a toll?
Are those carb rebuild kits any good?


1964-1/2 D Code Coupe - 289 V8, 4 Speed Toploader, 3.00 ratio rear, Autolite 4100 Carb, 15" tires, Pertronix ignition
     Thread Starter
 

2/17/2021 7:10 AM  #47


Re: Autolite Tune Up

I think you guys talked me into keeping the Autolite carb... I'm planning on ordering a rebuild kit from Mike's Carburetors. He seems to be quite knowledgeable and sells the parts. He also has a YouTube channel on rebuilding the carburetors.
Hopefully this works out... I am considering using the left over cash to buy a new intake manifold, if its worth doing (see other thread).
Stay tuned...


1964-1/2 D Code Coupe - 289 V8, 4 Speed Toploader, 3.00 ratio rear, Autolite 4100 Carb, 15" tires, Pertronix ignition
     Thread Starter
 

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