Need diagnosis help, Please

[Anonymous]

Hey guys,

Im running Bosch Platinums plugs in my 66stang. Stock ignition, and an Autolite 1100.
I have a lot of soft,black soot on my plugs. I understand this may be a rich mixture condition, symptom of a weak ignition, or too cold a heat range on the plugs.
I'm soon going to upgrade to Pertronix I, and the coil. I may be gapped too much on my plugs, I think I need to be between .32", and .36" for stock setup, and it looks more like .40"-.45", but I'll check tonight after I pull them and re gap some new plugs.
My issue is not knowing how to tune the Autolite 1100 to lean it out a bit.
1. Do I just turn the mixture screw one way or the other, and if so, where on the carb is this screw...

2. what, if anything else would I tinker with on the carb, where at on the carb do I tinker, and how do I know I've done any of this correctly.

I have an exploded view printed out of the 1100, just need some wrench turning, or screw driver turning as it may, advice.

Thanks guys
2.

 

[CZLN6]

Howdy 2:

What you're asking is a book by itself. This forum is not the place for a book.

Start by assessing that what you have is working properly, no leaks and at operating temp. No high speed or low speed misses and a good shot of fuel when the accelerator is depressed. Fuzzy black soot on the plugs could be too cold a heat range plug of something else. The Petronix and coil are great upgrades, but they cannot compensate for a worn carb or distributor.

Next determine that your automatic choke setting is as lean as it can be and still start and drive properly when cold. Make sure the choke is completely open when the engine is warmed up. Make sure the float is properly adjusted and not sticking open. If either is not working properly you may be in for a carb rebuild. The instructions in a rebuild kit are very helpful.

You have two slotted screwdriver adjustments on an 1100. One sets the idle speed. It is located on the throttle shaft and moves with the throttle shaft when the throttle is opened. Turning this one in will rains the idle speed. Set the idle at about 600 rpms- no higher. The other is a screw that goes into the base of the carb. They are frequently brass, not always, and usually have a tension spring on the shaft to help it hold its set. this is the low speed air screw. It adjusts the richness of the idle primarily. It helps with transitions somewhat.

With the engine off, start by turning the screw slowly in, counting the turns it takes to gently reach a stop. Remember the number of turns. Now back the screw out 1 1/2 turns. Now start the engine and let it warm up thoroughly- choke completely open. it will do no good to tune the idle screw if the choke is closed and on fast idle at all.

Once the engine is warmed up and off choke, slowly turn the screw in until engine rpms begine to drop. Now, start backing the screw out listening to the rpms. The engine should speed up as you back out the screw. At some point it will not continue to speed up. That point is your best setting. You may need to reset the idle speed with the first screw. If the idle gets too high it will effect the SCV vacuum signal to the carb and not give you a true reading on the idle air screw

Now drive the car. If all is correct it should work fine- no hesitations, surges, misses, smoking or stalling. It any of these things happen, it is not due to your low speed air screw setting. You can coverup a weak accelerator pump by setting your idle on the rich side.

Also make sure your initial advance setting is correct for your situation.

That should get you started.

Adios, David

 

[wsa111]

Follow the advice david gave. If your plugs are still sooty, scrap the bosch's & use autolite AP46, which is a hot plug, then set your idle speed 25-50 rpm's above specs. Then turn the idle mixture in-clockwise till you get a 25 to 50 RPM drop in idle speed to the correct idle specs. This is the lean drop method, by doing this procedure & still maintaining a decent idle it will put your idle mixture out of the 12-1 ratio which is too rich & closer to 13-13.5 air fuel ratio for improved fuel mileage & stop the stinking rich idle mixture. If you have access to a air fuel analizer or emisions checker this is the way to set your idle mixture. Ninety percent of self tuners always go the to rich side because they have never professionally used the proper analizer. If using the lean drop method causes hesitation problems you need to look at a low float level, if too rich a too high of a float level.
The autolite 1100 carb works better with a slightly higher float level to keep it from stalling when pulling into driveways or any operation that caused the fuel to uncover the idle tube in the carburetor.
Hope that fine tunes your carb-good luck. William

 

[Anonymous]

Thanks David and William, that'll get me on the right path. I'm also going to upgrade soon to a Holley 5200, but I want to pinpoint this issue first and resolve it with the setup that's currently on the car

I appreciate it, Kelly

 

[BIGREDRASA]

All that William and David said, plus one more thing.
Between the carb body and choke spring adjustment (The round thing used to set choke tension.), there is one other flathead screw adjustment. This is called the "High Speed Idle" or cold idle adjustment. You will notice that when the choke closes, this other screw rides on a "cam," which allows the idle speed to increase when the choke is closed. The cam should have a "<" mark on it, where the high speed idle is set. This is done with the engine at operating temp.
To check if your rich condition is happening during normal operation, and not just during idle, you will need to set this screw on the cam, and crank the speed up to about 2200 RPM. Remember, this is with the engine at operating temp.
Using a piece of cardboard or your hand, cover the airhorn gradually. If the speed immediately starts to drop, you're rich. If the speed doesn't start to drop until about 2/3 or 3/4 covered, you're OK. If you were running lean at cruise, then the speed would go up as you block the air horn.
This test would help you eliminate the power valve or a low/defective float as the cause of your richness.
Hope this helps/is clear enough. 8)