72 246 GT - Idle Cam Position & Adjustment...how?

Welcome to the world of janky early analog emission control systems. I wish I could help but this is the main reason why I bought a euro dino. Years ago I wrestled with British emissions systems of the same era and swore never again. Unless you’re trying for a platinum award I’d just get rid of as much of it as you can and enjoy your retirement driving your car.

 

Hi, and thanks for the kind words about my thread from 2012(!). Yes, I went all out on that one. Glad somebody noticed.

Now for the adjustment of the cam. The problem you experienced with starting and maintaining the idle at cold start is probably not caused by the adjustment of the cam. When it is working, it barely makes any difference. Better to check for possible ignition problems or clogged idle jets. Then adjust the idle mixture and set the idle for 900 to 1000 rpm when warm. If everything is normal, the idle when cold will then be quite low, but it should not stall. You should be able to easily keep the engine running with just an occasional blip on the throttle. Once you get the start and idle to be smooth and normal, you can then proceed to set the idle speed cam. Mostly for looks, though.

The adjustment screw pointing at your cam looks to be set too far away. The way I did the adjustment was to run the engine until warm, and then set the adjustment screw so that it had only a slight clearance to the disc. When the engine is cold, the adjustment screw should then be riding on the disc and forcing the throttle linkage to a higher idle speed. That is in theory. In reality it does not work well at all, but it may help a bit. It is simply a way to raise the idle when cold. It does not affect mixture etc., so it could hardly be the cause of your problems with cold running.

And yes, the picture of my engine was in cold condition. There should be a slight clearance to the disc, although it is hard to see.

 

Correction: The adjustment screw should be in contact with the disc when the engine is cold, as in the picture. Clearance only when engine is warm.

 

Yours (with the cam thing completely disabled) is how many of the carbed models wind up being adjusted. In that condition, it's up to the Driver to "squirt" extra fuel and add extra air as necessary using the acc. pedal during cold start up to keep it running. The cam just opens the throttle more when cold (only adds extra air) -- you'd also need to use the choke to add extra fuel -- and that can be a little risky on the cat-equipped carbed cars and risks fouling a plug or two on the non-cat cars as the choke mechanism in DCNF carbs opens well, but sometimes doesn't close so well (even though the Driver returns the choke lever in the cabin to the fully-closed position).

 

The 20 mark on the cam relates to the engine temp at 20 deg C and that should align with the adj screw. If its out of sync.then remove the cam and relocate the bi mettalic strip. If operating correctly, from cold (20C) the throttle linkage is moved by the cam which in turn operates opens up the carb buterfly's & the accelerator pump circuit, no different to you squeezing the gas pedal.

Not worked on the Dino setup but the idea carried over onto the 308 carb cars, it doesnt work as the 50 + year old bi mettalic strip doesnt have the energy to move the throttle linkage to increase the idle speed.

As others have said, leave it in a position so it doesnt work and check your idle jets, if its been sitting for a few months then these can clog up. First sign is popping from the exhaust or carb throats when decelerating.

Tony

 

Sorry, but I do not have that US Dino any longer. Have an M-series Euro model now.
But Tony explained the position of the cam so you can set it to where it looks good.
And best of luck to you in chasing down the real problem with your cold running condition by checking "the usual suspects."