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6/16/2016 4:04 PM  #1


I need an autolite 4100 carburetor expert

Backstory:
About 10 years back I parted out a 61 Galaxie to part out and the engine came with a 600 CFM Autolite 4100.  As I was parting out the car I was able to fire it up and drive it in and out of the garage to work on it.  Carb worked well no issues and when the time came I removed the carburetor, drained the fuel from it and put it on the shelf.  I heard rumors about how good these carburetors are and figured I would install it on something eventually.

Recently:
I decided to replace the Edelbrock 600 CFM carb currently on the 302 in my Galaxie with the Autolite 4100 that had been sitting on the shelf for years.  The install was simple and the engine fired right up.  (started with the setting the carb had had on its previous engine idle mixture screws two turn out) above 2000 RPMs engine runs well, you can feather the throttle and there is no hesitation, rough running or issues.  From 1500 RPMs to 2000 RPMs it runs rough but in a "mechanical" sort of way, what I mean is if the idle speed screw is set so the minimum RPM is 1500 than it will hold there for a few seconds, surge up to 1700 RPMs and hold there for a few seconds before changing again.) below 1500 RPMs it stumbles down in RPMs about 200 RPMs at a time (each stumble holding there for a few seconds)  until it drops own around 500 RPMs and dies.  I have tried adjusting the idle mixture screws both in and out and they seam to have no effect.  I have also had the top of the carb of and it is not filled with junk or coated with varnish.  Carb has a manul choke so I know that that is not the issue. Any suggestions as to what might be wrong with this carb and or how to fix it??


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6/16/2016 4:16 PM  #2


Re: I need an autolite 4100 carburetor expert

For starters any 1.12 venturi big block 4100 CANNOT be adjusted to work well on a small block. There are even a number of 1.08 venturi 4100's that were big block smog carburetors that will not work on SBFs. They were fabulous, smooth and economical carburetors when the right one was used for the right application.  Unfortunately, Autolite never broadened their appeal by publishing values for things such as the porting in the main body itself as well as the various booster values.  I got fortunate when I picked up a '66 small block carb for my '65.  It had the right jets and the right boosters in it.  Many that you might find today, even with the correct CZ number, have been bastardized.  I bought a correct numbered '65 SB carb and it had the wrong boosters in it.

Here is a carb forum.  It used to be excluslively Autolite but now it is more general.  Still there is a lot of 4100 knowledge on it (as much as anyone can know).  This is where I learned all I know about Autolites, back in the day when it was exclusive.

http://www.network54.com/Forum/88781

Last edited by boomyal (6/16/2016 5:34 PM)

 

6/17/2016 10:28 AM  #3


Re: I need an autolite 4100 carburetor expert

Daze, a couple of things worth checking.  Check the primary throttle shaft for wear - usually on the throttle linkage side.  Just wiggle the throttle lever up and down and side to side.  There should be very little wiggle.  And, check for the secondaries closing smoothly.  They can get gunked up and not close fully.
I have a 1.12 on my 302 and it runs well.  It was a "quadrajet" conversion done by Jon at Pony Carbs probably 15 years ago.  He took the 1.12 carb, and put plastic inserts into the primary venturii to get the carb down to the 380 cfm or so.  It worked really well for about 12 years, then the ignition coil went bad, I got a backfire through the carb, and it melted the venturii inserts.  So, I took them out, cleaned and re-gasketed the carb., and am still running it with no problems.  It is surely not as peppy as the Pony Carb modified carb., but it runs well.
Good Luck.

 

6/17/2016 12:33 PM  #4


Re: I need an autolite 4100 carburetor expert

Daze,
Take a look at the power valve I"ve found these corroded up even in running carbs, off idle to around 2k is where these operate.


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6/17/2016 6:57 PM  #5


Re: I need an autolite 4100 carburetor expert

I would venture to guess the idle circuit could use a blast of cleaner and compressed air and the primary float needle dried out and isn't seating well.

It would be well worth your time to get a Echlin rebuild kit from Napa. The beauty of the 4100 is its simplicity, I actually find it a joy to tear down and reassemble.

Pablo, if I ever get around to turning more venturi reducers ala Pony Carbs I'll pm you.

 

6/17/2016 10:26 PM  #6


Re: I need an autolite 4100 carburetor expert

I will reiterate!  History and experience has shown that big block 1.12  Autolite 4100's cause all manner of intactable problems when used on small blocks

Last edited by boomyal (6/17/2016 10:27 PM)

 

6/18/2016 11:19 PM  #7


Re: I need an autolite 4100 carburetor expert

Thanks to everyone who responded.  there is lots of good info here that I can use.

Pablo wrote:

Check the primary throttle shaft for wear - usually on the throttle linkage side.  Just wiggle the throttle lever up and down and side to side.  There should be very little wiggle.  And, check for the secondaries closing smoothly.  They can get gunked up and not close fully.

Good things to check, however those things were fine, I checked both of them before the carb went on the car.

Pablo wrote:

I have a 1.12 on my 302 and it runs well.  It was a "quadrajet" conversion done by Jon at Pony Carbs probably 15 years ago.  He took the 1.12 carb, and put plastic inserts into the primary venturi to get the carb down to the 380 cfm or so.  It worked really well for about 12 years, then the ignition coil went bad, I got a backfire through the carb, and it melted the venturi inserts. 

I am glad you mentioned the "Spreadbore " technique that poneycarb used.  I found a FAQ from their old website with info on the mod.  I also found several pages where inserts were made using a copper tubing reducer.  The way they did t leave a little something to be desired but I believe I can use their idea and do the same with a little finesse



bulletbirdman wrote:

Daze,
Take a look at the power valve I've found these corroded up even in running carbs, off idle to around 2k is where these operate.

Jon Richard wrote:

I would venture to guess the idle circuit could use a blast of cleaner and compressed air and the primary float needle dried out and isn't seating well.

It would be well worth your time to get a Echlin rebuild kit from Napa. The beauty of the 4100 is its simplicity, I actually find it a joy to tear down and reassemble.

​I have ordered a rebuild kit for the carb so I will replace all of that.  thanks for the suggestion.

boomyal wrote:

For starters any 1.12 venturi big block 4100 CANNOT be adjusted to work well on a small block. 

boomyal wrote:

I will reiterate!  History and experience has shown that big block 1.12  Autolite 4100's cause all manner of intactable problems when used on small blocks

Boom thanks for the input.  You are not the first person I have heard say that , however I get mixed reports.  Others like Pable have had success.  I don't think it is quite a clear cut as a 1.12 4100 won't work on a SB.  There are to many variables, intake, heads, displacement and so on.  In my case its a performance 302 with high flow aluminum intake and heads.  It is also a rebuild so instead of being a 302 its actually a 309.  I will take your info under advisement.  I plan on rebuilding the carb and sleeving the venturi so if it works I will have some info to share but if it doesn't work I will be the first to admit that I should have listened to your experience.  either way should be a fun project and worst case scenario I will have a freshly rebuilt carb to list on eBay  
 


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6/19/2016 1:25 AM  #8


Re: I need an autolite 4100 carburetor expert

I have still not found any satisfactory information source as to what all Jon Enyert did for the spread bore conversion. I  know the primary venturis are reduced to 1.00" and my particular unit came back with a "K" stamped primary booster.

I  have a second K booster and do intend to measure all the orifices with go/ no go gauges to determine if he had resized idle air bleeds or emulsion tubes etc.. but I can tell you for sure he had the primary float level set very low, too low in fact for the accelerator pump to prime. Honestly it worked ok but I wasn't extremely impressed with his approach, looks like the reducers increase the signal and the float setting leaned it out at lower rpm range, modifying the fuel curve enough to be usable on a smaller huffer. It worked but his own stance was that it was second best to the 1.08" and merely a bandaid for the scarcity of the 480cfm units.

I agree with boomyal about the 1.12 big block unit being wrong for a stock small block, but with performance mods like yours is OK. It won't have the lower end response and cruise characteristics like the 1.08" but with what you have can work well when you get on the gas.

Last edited by Jon Richard (6/19/2016 1:29 AM)

 

6/19/2016 5:37 AM  #9


Re: I need an autolite 4100 carburetor expert

Day, google Mikes carburetors. Good source for parts and info including some videos. I'd contact him for further discussion.

 

6/20/2016 10:39 AM  #10


Re: I need an autolite 4100 carburetor expert

[url=profile.php?id=40]boomyal[/url], Thanks for the link to the carb forum!!  I have done a lot of reading and what I have found tells me that if I sleeve the venturi and change the jets I should have a carburetor that is good for any SB however it will be almost perfectly suited for my SB because it is in my Galaxie.  I found it interesting as I was reading that the difference between the 1.08 and the 1.12 carbs has more to do with car size and how the weight of the car loads the engine rather than venturi size.  That is why the big block 1.08 carbs still don't do as well on most small blocks because most small blocks are in small cars.  I could be totally wrong but once I get my Carb rebuilt and setup for my 302 it should be about perfect for my application. at least that is what I am hoping

Its nice to find a nugget   What I mean to say is, like I said before, I have heard from many that the 1.08 will not work at all on a small block and I have heard from many others that it can be made to work well.  Obviously both side are correct based on their experience.  I knew that variables like displacement and how the engine is set up were obviously factors, but the weight of the car is a major factor that I hadn't considered and is the "nugget" I attribute to so many conflicting results. 

I will post more as this project comes together.


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6/20/2016 1:02 PM  #11


Re: I need an autolite 4100 carburetor expert

Daze wrote:

I have done a lot of reading and what I have found tells me that if I sleeve the venturi and change the jets I should have a carburetor that is good for any SB however it will be almost perfectly suited for my SB because it is in my Galaxie.  I found it interesting as I was reading that the difference between the 1.08 and the 1.12 carbs has more to do with car size and how the weight of the car loads the engine rather than venturi size.  That is why the big block 1.08 carbs still don't do as well on most small blocks because most small blocks are in small cars.  I could be totally wrong but once I get my Carb rebuilt and setup for my 302 it should be about perfect for my application. at least that is what I am hoping

You're not totally wrong but that's only half the story. The fuel curve is metered through the booster clusters, which are designed for whatever signal strength that is determined by both the venturi size and air velocity.

I think what boomyal is saying is that Ford never published the info needed to identify differences in boosters and without that modifying these becomes a lot of trial and error.

To get it "really right" you'll need to map your fuel curve and be prepared to make changes to things like the idle air bleeds and emulsion tubes- jet changes and power valves won't get you there.

It can be made to work but to really know accurately it's a bit tougher to do than on something designed to be tinkered on.

Looking forward to your follow up.

 

6/20/2016 1:26 PM  #12


Re: I need an autolite 4100 carburetor expert

Jon Richard wrote:

.......I think what boomyal is saying is that Ford never published the info needed to identify differences in boosters and without that modifying these becomes a lot of trial and error.

Identifying values is  only one of the problems, the other is obtaining boosters once you are able to identify the ones you may need.
 

Last edited by boomyal (6/20/2016 1:26 PM)

 

6/21/2016 11:01 AM  #13


Re: I need an autolite 4100 carburetor expert

Jon Richard wrote:

To get it "really right" you'll need to map your fuel curve and be prepared to make changes to things like the idle air bleeds and emulsion tubes- jet changes and power valves won't get you there.

I totally agree with you that there is more to this than jet size and venturi size however I don't have the knowledge base to change more than those two things.  It will be interesting to see if it can be "made to work", and if so how well with the modifications I can make.  

The reality is that setting up a carburetor to function with the best fuel curve and efficiency is no where near a "one size fits all" proposition and more of a "one size fits one" kind of thing.

If you take a carburetor and tune it for a bone stock 289 and get it dialed in to be a perfect mach for that engine, you could put that carb on any 289 that is set up the same way and is bing used for the same type of application and the carburetor should function equally as well on the second engine.  However if you leave it on the first engine and begin making changes, than the perfect tune is going to move away from being perfect as changes are made.  Headers, aluminum intake and heads as well as a change in cam specs when changed from bone stock will basically make that engine totally different from the carburetor's perspective.  I know that some carburetors are less effected by changes, but others are far more sensitive.

I have to wonder if that is why the 4100 has the reputation of being such a fantastic carb when set up correctly but also has so many issues when not correctly matched.  Is it possible that it is less resilient to change?  I compare it to the edelbrock performer.  You can take a 600 CFM edelbrock and put it on a 289, 302, 337, 347, 351W, 351C, 352FE or 390FE (all set up is configurations from stock to performance) and get it to work well with out changing the jets or modifying anything in the carb, yes it would be better with the correct tune but can be made to function well on all those engines right out of the box.  Obviously that is not the case on the autolite 4100 and the more research I have found, the more different versions of this carburetor I have found other than the venturi size.  I figure if Ford used so many different versions of the same carb based on application than that carb must not be as good at dealing with changes to the system.  On the flip side when set up correctly the 4100 is arguably a way better carburetor than a properly tuned edelbrock so I guess the trade of is performance and efficiency for versatility, and I wonder if thats why Ford moved away from the 4100. One size fits many is a whole lot cheeper to mass-produce than one size fits one.
 


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6/21/2016 12:15 PM  #14


Re: I need an autolite 4100 carburetor expert

Daze wrote:

I totally agree with you that there is more to this than jet size and venturi size however I don't have the knowledge base to change more than those two things.  It will be interesting to see if it can be "made to work", and if so how well with the modifications I can make.
 

Yes all the way around including the portions I didn't quote.

I'm betting yours will work fine, I was just emphasizing the point that how well is proportionate to how deep one is willing to go.

As far as knowledge base the best info I've found is usually about Holleys because the same principles of operation apply. Emulsion, transition, enrichment.., if you have an A/F ratio, tachometer,  and vacuum gauge you just need to be willing to solder/ braze up passages and re drill since like boomyal says good luck getting other boosters and knowing if they're correct.

I never leave my motors stock and I'm enamored with these Autolites so that's just the reality of what a mildly obsessive compulsive wrench head needs to resort to without aftermarket support.

Look at it like an opportunity to self teach and you'll come out the other end being the new 4100 guru with a sweet running Galaxie.

 

6/22/2016 9:51 AM  #15


Re: I need an autolite 4100 carburetor expert

Update, I solved 90% of my problems.  I didn't realize the 4100 needs a special base gasket and I had a vacuum leak.  After making the correct gasket I was able to get the car running fairly well, it still has some issues but I am hoping to address them in the rebuild and sleeving.  I will let you know how it goes as things progress.


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6/22/2016 10:16 AM  #16


Re: I need an autolite 4100 carburetor expert

That's great!

What gasket did you get? I haven't found one that fits the way I'd like and have been rolling my own.

 

6/22/2016 10:43 AM  #17


Re: I need an autolite 4100 carburetor expert

Daze wrote:

Update, I solved 90% of my problems.  I didn't realize the 4100 needs a special base gasket and I had a vacuum leak.  After making the correct gasket I was able to get the car running fairly well, it still has some issues but I am hoping to address them in the rebuild and sleeving.  I will let you know how it goes as things progress.

What intake manifold are you running it on?  If it was an Edelbrock, Holley or Weiend, it needs an adapter plate.

 

6/22/2016 4:43 PM  #18


Re: I need an autolite 4100 carburetor expert

Jon Richard wrote:

What gasket did you get? I haven't found one that fits the way I'd like and have been rolling my own.

The rebuild kit came with the correct gasket.  I wanted to try it but didn't want to use the one in the kit until after the rebuild so I traced it on to a sheet of gasket material and then cut it out with a razor blaze and some hole punches.

boomyal wrote:

What intake manifold are you running it on?  If it was an Edelbrock, Holley or Weiend, it needs an adapter plate.

I am running an Edelbrock intake and even from the beginning it had a spacer plate on there.  The spacer has the vacuum port for the PCV valve.  As I was going through my box of carb parts I found another 4-barrel spacer plate that is 1/4" thick that I had forgotten about.  It came with the 4100 on the 61 galaxie I parted out.  I compared that spacer to the gaskets I was trying to use and realized that a vacuum leak was probably my problem in fact I had to use both e 1" spacer and the factory 1/4" spacer to get the carb to seal correctly
 


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7/09/2016 8:32 PM  #19


Re: I need an autolite 4100 carburetor expert

I made an update to this project in a new thread.  Figured I would mention it so those of you who are following this thread would know about the new one.
 


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7/09/2016 10:18 PM  #20


Re: I need an autolite 4100 carburetor expert

Daze wrote:

Jon Richard wrote:

What gasket did you get? I haven't found one that fits the way I'd like and have been rolling my own.

The rebuild kit came with the correct gasket.  I wanted to try it but didn't want to use the one in the kit until after the rebuild so I traced it on to a sheet of gasket material and then cut it out with a razor blaze and some hole punches.

boomyal wrote:

What intake manifold are you running it on?  If it was an Edelbrock, Holley or Weiend, it needs an adapter plate.

I am running an Edelbrock intake and even from the beginning it had a spacer plate on there.  The spacer has the vacuum port for the PCV valve.  As I was going through my box of carb parts I found another 4-barrel spacer plate that is 1/4" thick that I had forgotten about.  It came with the 4100 on the 61 galaxie I parted out.  I compared that spacer to the gaskets I was trying to use and realized that a vacuum leak was probably my problem in fact I had to use both e 1" spacer and the factory 1/4" spacer to get the carb to seal correctly
 

Yeah, that's what I thought.  I was flummoxed by that on my 5.0 marine engine.  Never thought to look at the match between the carb base and the intake platform.  I ended up using a solid phenolic 1" spacer that I tapped a PVC fitting to.  Other than that, I was about ready to turn the 1" factory spacer upside down where the heretofore top side would seal positively on the intake platform.
 

Last edited by boomyal (7/09/2016 10:19 PM)

 

7/10/2016 7:56 PM  #21


Re: I need an autolite 4100 carburetor expert

You had counseled me once before to turn the spacer upside-down to avoid a vacuum leak in this thread-

http://fyi.boardhost.com/viewtopic_mobile.php

But be aware those holes taper to a larger diameter at the bottom so as to slow the velocity to help prevent the fuel from falling out of suspension,  so inverting the spacer will do the opposite and speed it up before it enters the intake plenum.

The last few base gaskets I got out of rebuild kits had the holes cut so large that there was barely enough coverage around the edges of the throttle bores, leading me to believe these are meant for between the spacer and manifold and not spacer to carburetor.

 

7/10/2016 10:18 PM  #22


Re: I need an autolite 4100 carburetor expert

Your link does not work JR..  That being said, I have both varieties of the factory spacers.  The one that ports the PCV to the secondaries and the one that ports around to the primaries.  I will measure the bores on both entry and exit.  I never thought to check that but they both appeared to be straight walled.

Last edited by boomyal (7/10/2016 10:18 PM)

 

7/11/2016 6:25 AM  #23


Re: I need an autolite 4100 carburetor expert

http://fyi.boardhost.com/viewtopic_mobile.php?id=1220

Hopefully the link works this time.

Yes I remember reading a post of yours regarding the differences between the spacers with regard to how the crank case gasses are routed differently.

 

7/23/2016 12:16 PM  #24


Re: I need an autolite 4100 carburetor expert

Pablo I sent you a PM


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