My 442 is getting finicky lately. I start it up one time and the idle is very slow - close to stalling in fact -but never does. I start it up another time it is too fast. I try and adjust but it keeps deciding what to do almost randomly.

So - I looked in the service Manual to see how to properly adjust the carb. But boy is it ever confusing. Given that I have a W-30 I am looking at the 4MC diagrams. BUT:

There is a Slow Idle Adjustment and a Fast Idle Adjustment. WHY? Do we need to perform both? If not then which one when?

The SIA and the FIA have different idle speeds 650 rpm is the desired speed for SIA and 1050 for FIA. Isn't that contradictory????

Also, not sure about the hot idle compensator? Is that the little screw kinda thing at back of carb that has a spring around it????

I do want to have the carb professionally rebuilt, but that was not on the schedule for this year (as I've been trying to get other things done). I was hoping to manage on my own with the carb untill 2011.

Incidentally I have looked for air leaks and find none. However, I do believe that the top gasket on the carb (that seals float bowel) is actually leaching gas. It always appears damp and when I wipe finger across I do get a smell of fresh gas on it.

Can anyone help??

 

Well, common sense says that there wouldn't be two specs if you didn't need to adjust both. They are different adjustments made with different screws. The slow idle adjustment is the normal idle adjustment screw that is used when the engine is at proper operating temperature. This screw is on the driver's side of the carb. The fast idle is controlled by the choke and is used before the engine is at operating temperature to keep it from stalling out. The choke operates a cam that has a series of steps. A SEPARATE fast idle adjustment screw on the passenger side of the carb rides on this cam and holds the throttle open more than normal when the engine is cold.

I suggest you spend some time reading the section of the CSM that describes how the carb works before you try to adjust the carb.

 

Joe.....I guess I am feeling a bit sheepish right now. You're right I should have studied things more. Instead of studying the book however I went and studied the carb for a while. Now it makes much more sense. The pictures in the book don't really give you that ah-ha thing nor are the descriptions very descriptive. Also, your explanation of the fast idle for cold starts was the key to understanding each step. It all fell into place for me at that point.

Based on what you wrote and how I see the thing working the problem might be the fast idle adjustments. Even though I get the problem when I restart hot I have a feeling it still coul be the problem. I'll be checking both.

One question remains however. What exactly does the Hot Idle Compensator do?

Also, I am debating reseating the mixture screws. The idle is a bit rough and I wonder if folks who have done that find it helps. The car has 43K miles and perhaps the screws should be adjusted as per the instructions in the CSM.

 

the hot idle compensator(hic) is used to compensate for high underhood temperatures that cause the fuel in the carburetor float bowl to vaporize more readily, thus richening the fuel mixture especially at idle. the hic accomplishes this by letting a small amount of air to bypass the throttle valves/metering system when the temperature of the hic rises to a pre-determined value, thus leaning the mixture to help hot idle quality. the higher the underhood temps are, beyond the temp at which the hic starts to open, the further the hic valve opens. the hic is a simple bi-metallic strip with a tapered valve attached to the strip. on the rebuild bench, many of theses hics are found to be partially open when they shouldn't be. since the hics are now unobtainable new, repair must be effected if they are found to be leaking. hics were used primarily on air conditioning-equipped vehicles. when adjusting curb idle speed and mixture, the hic should be held closed by pushing and holding-in the spring-loaded pin that protrudes through the hic cover on the rear of the carb.

seat the idle mixture screws lightly, don't tighten them. the basic starting adjustment is 2.5 turns out from seated.


bill

 

If the choke is working properly the fast idle should not be engaged on a hot start. Of course, that all depends on how hot, how long the car has sat, etc.