Topic: Autolite 4100 Carburetor Gasket

[markb0729]

I've been trying to track down an engine miss that starts to occur at 1200 RPM and above.  I've worked out a few issues with the ignition system and think that it's in good working order.  I've already looked for external vacuum leaks around the carburetor and intake manifold and found none.  I'm using FelPro 60059 gaskets for the carb to spacer and spacer to manifold connections.  I took a second look at this gasket and it does not seem right.  It looks like there will be a lot of leakage around the bores of the carburetor and it barely covers covers the perimeter base of the carburetor.  Is this what the stock factory gaskets look like?  I would think the gasket should seal around the carburetor bores?  Does anybody make an exact duplicate of the factory gasket?  Worse case I could make my own but i'd like to know what the original gasket looked like.

[J_Speegle]

Wow - not even close - yes the gasket should cover up to the inner edge of each those "bores" 

If you can't find the one you need. They are out there just have to find the source and a good number

If you need to you could use that gasket as a pattern for the outer shape then transfer the four cutouts to the pattern. If you go this route always make 3 or 4 while your at it.

[rocket289k]

Hi there,

I had a very good experience with gaskets sourced at Mike's Carburetor Parts.  He also stocks nice brass floats too.  I can't vouch for the bottom gasket.  I purchased a float bowl gasket from them and some brass floats and was very happy with the results.

Gaskets - http://www.carburetor-parts.com/Autolite-4100-Gaskets_c_588.html

All his Autolite carb parts - http://www.carburetor-parts.com/search.asp?keyword=autolite&search=search

Ron

[jwc66k]

I reused the old carburetor to spacer gasket when I rebuilt the 4100 on my 65 GT last year. The one in the kit just didn't "look" right. Everything else in the kit was OK though.
Jim

[markb0729]

Hi there,

I had a very good experience with gaskets sourced at Mike's Carburetor Parts.  He also stocks nice brass floats too.  I can't vouch for the bottom gasket.  I purchased a float bowl gasket from them and some brass floats and was very happy with the results.

Gaskets - http://www.carburetor-parts.com/Autolite-4100-Gaskets_c_588.html

All his Autolite carb parts - http://www.carburetor-parts.com/search.asp?keyword=autolite&search=search

Ron

Thanks Ron.  I clicked on the link for the carburetor gasket and was surprised to see that the website was recommending the use of the square bore gasket over the gasket with the 4 holes (See pic from website below).  I've read that people use the square gasket with aftermarket intake manifolds but my intake manifold is a stock cast iron 4 barrel Ford intake.   The description of the gasket from the Mike's Carburetor Parts website states...

"Autolite 4100, 4 barrel flange gasket. Fits all 4100 series carburetors. Some of the old gaskets had individual holes for each bore. These are the replacement and open style." 

Their is no mention of stock vs aftermarket intakes.  Does anybody know if this type of gasket be used along with a stock intake manifold and spacer?  Does anybody have any experiences using 2 square carburetor mounting gaskets in a stock application?

I reused the old carburetor to spacer gasket when I rebuilt the 4100 on my 65 GT last year. The one in the kit just didn't "look" right. Everything else in the kit was OK though.
Jim

Was the kit from Mike's Carburetor Parts or another vendor? 

I'm surprised no one knows of a vendor that sells the correct fitting carburetor mounting gasket.  You would think there would be more complaints of poorly running engines.

[66candy]

Hello Mark.....I've read your story on the VMF about your problem. I have more or less the same issue: a slight miss at idle up to about 2000 rpm. Tried and checked everything. Vacuum leaks, compression, timing, points instead of pertronix, coil, other 4100 carb AND gaskets!

I've cut my own from 1 mm thick gasket material but this had no effect at all!

[jwc66k]

Was the kit from Mike's Carburetor Parts or another vendor? 

The rebuilt kit's brand was Walker.
Every once in a while, the power valve does not seat well. If you have the old valve, stick it back in for a sanity check. It's gasket is another overlooked area too.
I notice you have the "adapter fitting" on the choke housing for the steel line routed from the exhaust manifold. The cover looks stamped vs. cast. Just a "notice".
Jim

[markb0729]

Hello Mark.....I've read your story on the VMF about your problem. I have more or less the same issue: a slight miss at idle up to about 2000 rpm. Tried and checked everything. Vacuum leaks, compression, timing, points instead of pertronix, coil, other 4100 carb AND gaskets!

I've cut my own from 1 mm thick gasket material but this had no effect at all!

Your miss seems to mostly happen in the RPM range where I don't have a miss.  A random miss on my engine starts around 1200 RPM and continues through the upper RPM range.  I did have a miss at idle and the engine would occasionally "stumble" at idle.  Through troubleshooting, I found out my new after market yellow top coil had a bad resistance reading in the secondary circuit.  For testing purposes, I bought a coil at the local auto parts store and the miss and stumble at idle went away.  I also had an occasional miss in the timing light strobe at all RPMs on all cylinders with a Pertronix 1 installed.  I replaced the Pertronix 1 with points/condenser and the timing light strobe miss was not evident anymore.  The engine is running much better with the new coil and points/condenser installed but the random miss starting at around 1200 RPM persists.  Here is the link to the VMF site if others are interested in mys engine miss saga:

http://forums.vintage-mustang.com/vintage-mustang-forum/1023937-troubleshooting-engine-miss-66-289-a.html

I believe the ignition system is up to snuff so I'm taking another look at the carburetor and air intake system hence why I'm looking at the carburetor and spacer mounting gaskets.  With the engine at idle and a vacuum gauge hooked to the intake manifold there is slow movement in the vacuum from about 17.5 Hg to almost 18.5 Hg.  I feel this may be an indication of a slight vacuum leak or a carburetor tuning problem.  It's discouraging that you made a correct fitting carburetor mounting gasket and that did not help with your problem.  Did you make 2 gaskets; one for the carburetor to spacer and another for the spacer to manifold?  We have been down almost the exact same troubleshooting path with no luck.  Whats your next move?

[markb0729]

The rebuilt kit's brand was Walker.
Every once in a while, the power valve does not seat well. If you have the old valve, stick it back in for a sanity check. It's gasket is another overlooked area too.
I notice you have the "adapter fitting" on the choke housing for the steel line routed from the exhaust manifold. The cover looks stamped vs. cast. Just a "notice".
Jim

Unfortunately, I had the carburetor rebuilt and don't have the original power valve.  I told the rebuilder that the carburetor was going on a stock build so I'm assuming he installed a power valve somewhere in the 7.5 to 8.5 Hg range.  I could take a peek and try to get some numbers.  Do you think the power valve could cause my problem?  I'm not sure when the installed power valve "kicks in" but the vacuum gauge is not in the 7.5 to 8.5 Hg range when the engine is missing.  I've been doing all my testing with the car in Park (not a road test). 

I was just looking at a Walker parts list for the 4100 and it also lists the square bore carburetor mounting gasket as also listed on the Mike's Carburetor Part's site.  The guy that rebuilt my 4100 sent 2 square bore carburetor mounting gaskets back with the rebuilt carburetor and said "Use the mounting gaskets I send you when you install the carb."  I looked at the gaskets he sent and figured he must be wrong and installed the horrible fitting FelPro 60059 gaskets shown above.  That's 3 different sources saying to use the square bore gasket.  Is the square bore gasket a better solution to the original 4 hole gasket supplied by Ford?  This is a stock Autolite 4100 carburetor, 1 " spacer with PCV port and cast iron Ford intake manifold.  I know the square bore gasket is not concours correct but I just want to get my engine running correctly.

[67gtasanjose]

Without reading through 3 pages over at the VMF site and since it has not been mentioned here yet, has anyone put an analog dwell meter on either of these examples? Points gap combined with correct dwell angle is a MUST to dial these cars in. The dwell angle has to be within specs & should not change as the engine accelerates or decelerates.
(This detail on vintage cars OTHER THAN GM's with the slide-up window distributor cap, is hard to get it perfect ~that slide-up cap design was one of the best things about vintage GM's ~now only if they would have put the darn thing up front of the engine like a Ford!)

[markb0729]

Yea, I hear ya on the little door in the distributor to adjust dwell, great concept.  I wouldn't be surprised if it was a bean counter thing where not having the little door would save a nickle in manufacturing.     

I replaced the Pertronix 1 with a NOS Motorcraft points and condenser.  Set the initial point Gap to .017 and checked the dwell with an analog dwell meter.  IIRC with an initial point gap of .017 the dwell reading was 25 at idle.  I closed up the point gap ever so slightly and the dwell is now set to around 27.5 at idle with no variation.  I do get a maximum dip in the dwell angle of about 1 degree (dwell reads about 26.5) when opening the throttle above idle and running the engine in the higher RPM range (lets say 2000+).  The dwell angle does not vary back and forth when holding at a specific RPM or revving up and down in the higher RPM range, it sits at 26.5.  With the engine at idle and a vacuum gauge hooked to the intake manifold there is slow constant movement in the vacuum from about 17.5 Hg to almost 18.5 Hg.  I also noted a vacuum variation at 1600 RPM with manifold vacuum at 21 Hg with a very slight variation (no more than .5 Hg) above and below 21 Hg.  The engine still has a random miss above 1200 RPM with these readings.  The vacuum gauge readings are why I'm back to looking at the carburetor and intake for adjustment or vacuum leak issues.

[sgl66]

If you have access to one, I would try another carb (brand doesn't matter) to see if the problem remains

[67gtasanjose]

If you have access to one, I would try another carb (brand doesn't matter) to see if the problem remains

not a bad idea...

Another option is if you know of a local company who has a gas analyzer (emission) tester. Even better with a dyno...Might be worth the bux to save a few migraines!
Like in many situations (not just car work) we'll often spend 3-4 times as much to"do it yourself" rather than pay some "crooked" shop just dying to stay alive in such a business.   

[markb0729]

If you have access to one, I would try another carb (brand doesn't matter) to see if the problem remains

I have 3 Autolite 4100 carburetors.  I had 2 rebuilt by 2 different rebuilders.  The second carburetor is installed now and was bench tested by the rebuilder.  The first one I installed definitely has a clog somewhere in the idle circuit on the drivers side.  I can turn the drivers side idle mixture screw in and out with virtually no affect on the engine.  I may order a premium carburetor rebuild kit from Mikes Carburetor Parts and rebuild the second (or third) carburetor myself so at least I know where I stand.  I considered buying a new Summit M2008 Series Carburetor number SUM-M08500VS (https://www.summitracing.com/parts/sum-m08500vs/overview/) but I'm hesitant on spending $300 on a carburetor I would only be using as a test.  Ugh!

[markb0729]

Another option is if you know of a local company who has a gas analyzer (emission) tester. Even better with a dyno...Might be worth the bux to save a few migraines!
Like in many situations (not just car work) we'll often spend 3-4 times as much to"do it yourself" rather than pay some "crooked" shop just dying to stay alive in such a business.

Yes,  I'm starting to get agita over this problem!  I would be more than happy to work with a local company that could help me figure this out.  I live in Burlington county New Jersey.  Does anybody have a suggestion or can point me in the right direction in finding one?

The rebuilder of the my engine is known as a Ford mechanic and builds his own hot rods for racing.  He seems to know his way around a wrench.  Anyway, he returned to me an engine with lots of little issues to work out.  I'm really hesitant to return to him. 

Last fall, I took the Mustang to a supposedly reputable classic car shop specializing in Fords and for my trouble I got a big bill and a car that ran "a little" better.  This shop supposed rebuilt the first 4100 for a second time and it has a clogged idle circuit!  I was very disappointed to say the least.  My faith in finding competent rebuilders and mechanics who can help figure out the problem has been significantly diminished hence why I'm spending a lot of my own time trying to figure this out.  I'd like to work with a local shop if I can find a competent one.