Help with fast idle adjustment

Hello,

The fast idle works properly on my car in that it holds the engine speed up until I want to drive, the problem is that I'm having to put the pedal all the way down to the floor to kick the fast idle cam off in the morning after I warm the car up. The shop manual didn't say anything about that, other than how to adjust the cam for speed. My continental has a holley 4160 that will pull the fast idle off with just a touch on the gas pedal, which is where I would like the Buick at. Anyone know how I can do this?

Thanks,
Mike

 

Sticky or binding linkage and pivot points? Might want to consider spraying some aerosol carb cleaner on the linkage, and working it back and forth as the solvent dissolves any varnish or goo.

 

The bi-metal thermostats seem to age.

If yours is like mine you can try the higher hole at the top of the rod or bend the rod just a bit to shorten it. That's what the "U" is for, i figer.

 

One thing I have not seen in this scenario is the possibility that the choke coil is not properly heating up. If this choke is the divorced type, it depends on both the air cleaner and the choke stove to heat the coil. If either is not operating correctly, the result could be a cold coil, causing the choke blade to stay partially closed. Let us know...

 

The choke seems to work fine. On cold mornings the engine fires right up, and the choke is closed. I need to take a look at it to see if it is opening up all the way by itself. The car always runs and drives very well with no sort of carb issues once its warmed (even when cold). Once the engine is warm and once I have kick off the fast-idle, the choke is open, so it appears to operate correctly.

Should an "automatic" choke also lower the idle speed once the engine has fully warmed up?

Should I try finding a new thermostat

 

Rather than assuming that replacement parts are necessary, or what to buy, let's look at the system as a whole, and look for the problem using that understanding. The choke, which controls how much air the engine gets with delivered fuel, closes based on the tension created by the choke coil. As the choke blade colses, due to that tension, a link pulls up the fast idle cam, which holds the throttle part way open, providing the fast idle. First, let's make sure that the choke system opens correctly, and make sure that nothing is sticking. The choke coil gets its heat from two points, depending on the design. In the first or early design, the exhaust crossover in the intake manifold heats up, using exhaust flow through the passage. The coil, essentially sealed in this passage, heats up as well, allowing the coil to reduce its tension. This causes the choke blade to open, and allows the fast idle cam to fall, using gravity, to allow the idle to drop as the engine warms. The late choke system uses incoming heated air from two heat sources. The first is the incoming air from the heated air cleaner. This valve in the snorkel limits outside air from entering the air cleaner until the air temp reaches some temperature over 100 deg. This incoming air is pulled across the exhaust manifold, which heats it. This heated air then is pulled through the same intake crossover passage, further heating the air. The source for this draw is the vacuum passage in the housing, which creates a vacuum in the choke housing. This vacuum draws heated air utlimately from the air cleaner as perviously described. The route is then as follows: heated air in the air cleaner is pulled into the housing through a pipe which allows the air to be further heated by the passage in the intake. This doubly heated air heats the choke coil, allowijng its tension to dissipate, opening the choke, and allowing the fast idle cam to drop. This fast idle speed adjustment is on the passenger side of the carb. The slow or curb idle screw is on the driver's side. Try this: Start the engine cold, watching the choke. Is it closed completely? From your description it is. Do not try to watch the choke open, as the missing air cleaner will reduce the heating of the coil, which, in many cases, will prevent the choke from opening more than 3/4. This condition will cause the fast idle cam to drop only part way, raising the idle. You might also try pushing the choke blade fully open when it is hot. If it moves farther open, the choke is not opening all the way. That is likely due to the tension spring, but make sure that the spring is heating completely. Try touching the air cleaner at a point where the snorkel meets the housing. It should be warm and getting hot. If not, the snorkel vavle is likely open, not heating the air. It is also possible, at this point ot check whether the choke housing is sealed by the gasket behind the choke t'stat. Heating is the most important thing to check, as it will lead to replacement parts not fixing the problem. This situation os propbably the most likely scenario, and how I fix some 85% of choke related concerns I see. Let's start with that scenario, and go from there. PM me w/questions id you like.