Ok guys. I've started to notice that 6 cylinder Mustangs are starting to pick up in popularity. And with this, I've also noticed a rise in carburetor problems. Well, this thread is going to try and help my fellow 6 cylinder owners make sure they have the right information regarding what carburetor they need. At the bottom I'll include a link to a site with some really good in depth information on how the problems work.
I've seen more than one thread, on this forum and others, where owners were having trouble with stumbling and stalling when trying to pull away from a stop and rattling under heavy throttle (this is actually pre-detonation, we'll get to that in a bit). I've heard people saying it's jet size, float level, fuel mixture, but in reality, it is something much more simple than that... it's simply the wrong carburetor. And after working on 31 (yes, I've rebuilt 31) Autolite 1100 carburetors in the last 6 years I hope to help you guys make sure you have the right carburetor on your Mustang so you don't have the same problem I did.
Just as a heads up warning, if you do have the wrong Autolite 1100 and your have pre-detonation (sounds sort of like a rattling sound) LET OFF. I learned the hard way... That is the fastest way to an engine rebuild as it blew the oil rings and the sides of one of my pistons to pieces. I was lucky it didn't damage anything else and I only had to re-hone the cylinder walls.
Right, so how can you tell if you have the right or wrong Autolite 1100. There were 4 varients of the Autolite 1100 used on the Mustang from 1965-1967, 2 for manual transmission cars and 2 for automatic transmission cars. The difference between the automatic and manual 1100s is a second pump. On manual transmission versions, there is 1 accelerator pump, located on the driver side of the carburetor. On automatic transmission versions there is a 2nd pump, located on the passenger side. This pump is there to help keep the car from stumbling or stalling when pulling away.. It's called the Anti-stall dashpot. You can use an automatic “double pumper” on a manual transmission equipped car (it won't do anything), but you can't use a manual trans
carb on an automatic equipped car.
Now, as I previously stated there are 2 different versions of each of these, and this is where it becomes slightly complicated. From 1965-1967 Ford used what was called the “Load-O-Matic” distributor on all 6 cylinder Mustang's that WERE NOT to be sold in California (we'll cover that in a bit). The Load-O-Matic distributor is only equipped with a vacuum advance. Now most distributors use a mix of manifold (or ported) vacuum, and centrifugal weights to compensate for speed and load. Manifold vacuum is very high when under light load, but as you accelerate it becomes weaker. Since that will not provide an adequate source of vacuum, Ford came up with a solution called the “Spark Control Valve”. It looks like a little wheel near the vacuum line input. This valve switches the Load-O-Matic's vacuum source between manifold (for light acceleration) and venturi vacuum (for load/speed)
Cars that were destined to be sold in California (such as my 1966 Sprint 200) were doomed to be equipped with a “Thermactor Emissions System”. Mercifully cars equipped with the emissions system got a standard dual advance distributor. These cars came equipped with a NON Spark Control Valve Autolite 1100 carb. The problem that I faced and people putting the SCV carb on their dual advance equipped cars is that under load the distributor is getting maximum advance because of both the venturi vacuum and the centrifugal weights trying to advance the distributor at the same time. This is what will cause the pre-detonation that will hurt your engines.
Starting in 1968 Ford did away with the Load-O-Matic distributor and the spark control valve and all cars gained the non SCV carburetor and dual advance distributor. Unfortunately, due to the high sales of 49 state Mustangs from 1965-1967 this means the market is absolutely flooded by the SCV 1100s. And many people over the years have bought cars that have had the horsepower sapping, useless emissions systems ripped out and thrown away, and as carburetors have worn out owners have bought the first cheap Autolite 1100 they find, just to pull their hair out trying to get the car to run correctly. For those of us who have the dual advance distributor, we also have the ability to (relatively) easily switch to an Autolite 2100 (2 barrel) or a Weber carburetor for improved performance and fuel economy (these both mix the air & fuel better than our little 1100). Owners of Load-O-Matic cars will need to either source a 1968 dual advance distributor or find a Duraspark distributor (available from Classic Inlines) but you'll have to change the carburetor at the same time.
I've attached 3 pictures, each labeled (couldn't find a non SCV manual trans
carburetor). I hope this long (sorry) article is helpful to my fellow 6 cylinder owners. Michael
Conversion kits (carburetor and distributors) are available through Classic Inlines Performance Parts - Home
For more in depth reading on the Load-O-Matic and SCV, here is their article. Classic Inlines Ford Six Load-O-Matic Distributor & Spark Control Valve