I’ve done Doc’s intake modification, and understand I should limit heat to the carb. What is the preferred method for blocking the exhaust crossover? Plug the holes on either side where the carb sits? What material? Do I still use that stainless plate?
Short version: use little brass home depot threaded plugs (1/8 NPT?), tap and thread the intake at the carb pad, run the plugs in and grind anything that sticks up flat. you can finish with an epoxy, JB Weld, etc.. or leave it alone, and the stainless spacer is really no longer required. The idea is that you want heat in the intake, but not in the carb pad area. There are various methods, but I've found this one to be the easiest and most reliable..
I buy the 1/8” pipe plugs that have the Allen socket and run the tap in far enough that when you screw the plugs in they are below the flat surface. Use a good four hole carb gasket and it will seal without doing any filling over the plugs. I also use anti-seize on the plugs to help seal them and make them easy to remove later if necessary.
High Jack.. I have a metal plate under my carb, without plugged crossover. When the car is fully varm, and held on the brake brakes in gear, with low rpm it wants to die, like a really big cam.. If I put i in neutral or give it a little gas it stops.. Can't find any vacum leaks, and switch pitch arm doesn't change anything when pulled/pressed. . Stock 65 401"..
Soren - I'm going through this right now on my 340. Was it running well before? When was the carb rebuilt last? Assuming the electrical side is good and adjusting the idle speed does not help (make sure secondary circuit is not "on") - Common areas are: 1)Vacuum leak - could be in the transmission module, power brakes, pvc hose, distributor advance. Pull each hose off the carb and suck air through each of them. You should be able to hold a vacuum (except PVC - just inspect the hose). 2) Pull the carb and check the plate. They will burn through. Replace it if you have any holes. 3) Idle circuit dirty: remove the idle mixture screws and squirt in carb cleaner. Blow in the hole with compressed air, repeat several times. If none of that works the carb may need a more thorough going through. Do it yourself (if knowledgeable) or send to Tom Telesco (telriv on this board). Note, the switch pitch arm should not affect idle.
The carb is a newish 750cfm manual choke edelbrock, but it have always done it.. Changed out the old Carter hoping it would solve the problem.. I have checked mulitple times for vacum leaks, and changed a lot of the hoses in the seach. Have tried spraying with flameble liquid around in the engine compardment, with no luck (engine rpm goes up, when sprayed into carb) The switch pitch arm was checked when another member asked if it was in high or low stall, but made no difference regardless of position.. Haven't checked the metal plate in a while. If I raise the idle rpm, the problem goes away, but the rpms are so high that the car wants to crep real bad, where with the "problem rpm idle" a single toe on the brake paddle is enough.. The hard part is it only does it when it fully varm, so my thoughts were that the gas "boils" when the flow gets low..
Do you mean warm is when the choke is off or later? The point I was trying to make is that a vacuum leak could be in the device at the other end. For example, I had a broken diaphram in the vacuum advance for my distributor. The hose looked fine, but I could suck air from the hose from the canister. Just to confirm, you've had this problem for awhile with the carter and you switched to the edelbrock to try to solve it. Do you have a tach? Some specific numbers would help, in neutral and in drive. Also, if you look inside the carb, do you see gas dripping off the venturi in the primary side when you turn the idle up to where it is smooth but creeps? And what rpm is that?
I never use the choke.. I only drive the car in varm weather.. I switched carb trying to fix it yes.. I have no tach, so I have no idea about rpm, other that it sounds and feels too high when the problem doesn't show itself.. I will try to suck air through the hoses, to be sure I've haven't got leaks further down, and will check the metal plate, possible blocking the cross over.. Thanks for the help..
If the metal plate was good when you switched carbs I doubt it has burned through already. It usually takes years and many miles. So when you start it cold I assume you blip the throttle to keep it running until it will idle. What happens then?
It usally sits for long periods between driven.. I tap the throttle until it starts, and then hold it a little until it will idle without "help".. Then it drives perfect, until driven 10 miles, and everything is 87 degress celcius, then it start to bug..
You got me - interesting and I do not know. Maybe Tom Telesco will chime in, or you can PM him direct.
That's the hard part.. Over the couple last years, I've driven the car 1000-2000 miles, and it never fails to start or never misses a beat.. My plugs are nice light brown, I have good power, 18 mpg at 60mph.. Just throwing thoughts now.. My dist has been recurved with lighter springs and heawier weigths, with total of 34 degress timing, without vacum, coming in rather early.. Could the timing be to low in idle, when "under load"? I haven't adjusted anything other than air screws and idle on the carb, could the float or something be off? The air screws (the 2 with springs) is IIRC 1,5 turn out, where it seems happiest..
Hijack it back...installed with electronic ignition conversion. Just have last bits of wiring left (choke and coil).
Doc - thats pretty! Soren - Certainly check your timing. If it was low, your idle would be lower, not higher. The vacuum advance pulls it back up at idle when the vacuum is highest (manifold port).
