308 carb-preferred method for raising idle speed?

the A/C loads the engine. if i recal correctly the ignition system is set to handle the load, unless ferrari used a soleniod to physically move the throttle. however i think they used a vacuum advance on the distributors.

 

Set the idle speed when the engine is hot at normal running temps (90 degrees C/195 degrees F).

On both driver's side carburetors there are screws where the throttle plate linkages rest on when at idle. Turn them clockwise - with the linkages disconnected - until they flow air equally to achieve the desired idle RPM. Re-check air flow when you re-connect the linkages.

I'm not aware of any devices Ferrari installed on the carb cars, to bump up RPM when A/C is on.

 

Greg
The way I understand it there are three ways to change the idle speed but they all require turning the screws. 1. Turn the throttle stop (idle stop) screws. This of course changes the throttle plate position. 2. Turn all the air bypass screws out equally say 1/4 turn which increases the air flow so you then have to turn the air/fuel screws out also to reestablish the correct fuel/air ratio. This will increase the idle speed without changing the throttle position. 3. A combination of both. In your case you might try the 1st way since you are only wanting to increase the idle a couple 100 rpm's. If your carb setup is like mine the only adjustment is made on the driver side carbs as changing these throttle stop screws equally changes the passenger side plate position... assuming the linkage is set up correctly. I would turn each of the two screws in 1/16 turn on the front and rear banks and drive the car to see if this is enought. If not maybe another 1/16. Write the # of turns so you can go back to the original setup if you want. If that doesn't work then I would caution you about too much adjustment with these screws because you can open a can of worms. However you can always turn them back. You might turn these screws back to the original set up and try the second way. If so use your synchrometer to keep the air flow equal on all throats. Now I know you don't want to do this but you asked....maybe just drive your car when it is cool out side. lol hth

 

I use the throttle stop screws also. When I did my carb adjustment a few years ago I set the idle up to 1100 rpm when engine was warm. I have disconnected the cold start device. So when I have the AC on it idles at 1000rpm. Also if you put a volt meter on the car you will find that you get the max voltage output around 1000 - 1200 rpm (13.6V) . So at idle with the AC on I get 13.2 V.
There is no device that Ferrari had put on the engine to bump up the idle on the carb cars. They might have done that with the FI cars where it is easier to do.

 

Greg,

Adjustment of the throttle stop screws is the proper way to adjust the idle speed.

Bill

 

I am absolutely not the foremost authority on carb adjustments but…I would not adjust your carbs by simply adjusting the idle stop screws on the left side carbs. When I got my 79 308 GTB almost 3 years ago it had a very erratic idle. I tried a number of adjustments in a very non-systematic manner. All I did was cause more problems. I will not touch any adjustment without doing a complete synchronization now.

Additionally, and others more experienced please feel free to correct me, the way I understand this there are three basic idle speed adjustments. Each row of carbs is controlled by the idle stop screw on the driver’s side carb. The right side carbs are adjusted by the adjustment in the linkage between the carbs. The left venturi in each carb is flow balanced to the right venturi in that carb via the depression balance screw. These should not often need adjustment. Since the 308 idles on all 8 venturies it is important that all 8 are adjusted to flow equally at idle.

The next adjustment is to ensure that the linkage picks all carbs together off of the idle stop. This can be affected by idle adjustment if there is not sufficient freeplay.

I have noticed that my idle will vary a couple hundred RPM with various weather conditions. I just live with that. Now that my carbs are adjusted properly this car runs absolutely great. As with any car, ensure that the ignition is absolutely perfect including timing before touching a carb adjustment.

 

Greg,

Yes, the 2-driver's side carbs are fitted with the idle speed adjusting screws. Adjustment of these screws also affect the passenger side carbs. Adjustment of these screws in the same amount, will not affect the over all balance of the rest of the linkage. If the idle adjustment screws are in contact with the linkage, and some times they are not, you shouldn't have to go more than about 1/2 to 1-flat clockwise to achieve the increase you are looking for. This amount of adjustment will be unnoticable at the pedal. There is no reason to disconnect or alter any of the linkage if the carbs are already in good synch.

Bill

 

Greg
I agree with Bill that small adjustments to the driver side idle (throttle)stop screws should not affect the overall performance of your car. As mentioned before make small increment changes and try it out to make sure you are not messing anything up. Again don't change these screws any more than necessary as too much adjustment here can cause problems. Also remember to adjust both front and rear equally and remember how much you turn these screws...you can always turn them back to the original settings. Now in theory any changes in one area of a carb setup effects all the other adjustments of the linkage and carbs but this small adjustment should not cause you any problems. If it does backtrack in small increments until you get the best settings. If still a problem go back to the original setting and take it to your mechanic to redo. Also you can just live with the inconveince.
Good luck and let us know how things turn out.

 

It's just my opinion but I would leave well eough alone. As you said, they run sweet now. It will give you a chance to pratice your toe/heal technique when using the A/C.