I just rebuilt my H30/31 carb and I have a question abut the settings on it. For the little idle screw, I understand I need to back it our 2.5 turns. Is this correct? And if so, does turn = 360 degrees?

With that set, the big idle screw needs to come out how far?

The problem was that the car would idle until warm, then die. Motor has been rebuilt, timing and valves are all in spec, so I suspected the carb since I could not adjust the idle with the big screw any longer.

UPDATE - It starts and runs great, till warm, (about a minute or so) then it dies. What is causing this and how do I adjust? I am very frustrated.

I need HELP!

Thanks in advance,
RC

To properly adjust the H30/31, you need to go back and forth between the big and little screws. To do this procedure, the car needs to be all warmed up and the timing etc needs to be adjusted. Start with the little screw about 2.5 turns out (1 turn = 360 deg, like you said) and set the big one out by about the same. Start the car and make sure the choke is open all the way (and the engine is warmed up) and use the big screw to set the idle speed to about 850-900 rpm. Then move on to the little one, start turning it in slowly while noting the engine speed, at some point while you're turning it in, the engine speed will start to fall off and it will start running rough (an maybe you will start to hear a little lean misfire). At that point, stop tuning it in and start turning it back out slowly till the idle speed picks up again and the engine smooths out. From the point where that happens, turn it out an additional quarter turn or so. Now go back to the big screw and set the idle speed back to 850-900 (it will probably be higher after you set the little screw, so turn it in if needed to bring the idle speed back down). Once you get the idle speed back to the proper range, go back to the little screw and repeat the previous procedure you did on it, then go back to the big screw to set the idle speed, and so on back and forth till no more change is needed to get the right mixture (the little one) and the right idle speed (the big one). It usually only takes 2-3 back-and-forths to get it perfect. After you go through this procedure it should purr like a kitten. Remember though, it's very important that the engine be fully warmed up and that the choke be completely open.

Brian,

Thanks. Good information. I think I may have a vacuum leak, or at worst a cracked head. So, once I fully investigate this, I'll go through the procedure and see if I can get this car running. I really want to drive her daily!

Ron

If you can get it running, try spraying WD-40 around all the points in the intake system where a leak could potentially occur: around where the end casting go to the heads, where the end castings go on the center section (if its a DP), where the carb goes on the manifold, etc. If you have a vacuum leak the engine will change RPM when you spray the leaking area. If you have any vacuum ports on the carb capped make sure the caps are tight and not cracked.