I'm about to set the idle to factory specs, but I need to know which screws are for what. The carb is a 4mv on a 68 430-4. There are 3 screws in the front. I circled them in the pic. Can you tell me which are what? I take it the bottom two are fast (passenger side) and slow (driver side) idle? If I'm right, what is the third one for? My manual says to adjust the throttle stop screw before adjusting the idle mixture needles. Is the one on the far right it?
The two bottom screws are your idle mixture adjustment for the left & right primary bores. The one screw on the far right is your idle speed adjustment. For initial setting of idle mixture, gently tighten the idle mixture screws untill they are fully seated, then back each screw out two and 1/2 turns. Once your engine is running and fully warmed up, gently tighten each mixture screw until your engine RPMs drop by about 50 (or it begins to develop a lean miss), then back the screw out 1/8 turn. The idle speed screw should be tightened until it contacts the throttle linkage tab, and pushes it about 1/16". If it is too tight, the primary throttle blades will be open too far, and your main metering system will engage during idle, giving you nozzle drip. Your idle speed once warmed up should be about 750-800 RPM in park, about 600 RPM in gear. Once your engine is idling, look down the primary bores. If you see fuel dripping from the primary venturis, you've got the idle speed screw tightened too far.
Once warm, you may be able to get the idle at 550 in gear. Cold, your engine will need to idle at 1000 RPM or above until the oil warms up and the mechanical resistance goes down. 550 RPM on a 430 Wildcat will be hard to manage until you have the idle mix and timing set perfectly. Just get it idling, then back it down to whatever you like. The manual is stating the factory idle specs for emissions, not performance.
Yeah you're right, I just read a little side paragraph in the manual that says these settings must be done exactly to reduce hydrocarbons and emissions. Save the planet or boost performance? Decisions, decisions.
One more thing...I noticed your ported vacuum advance connection on the front of the carb (above the right idle mix screw) is disconnected. You need to run a vacuum line to the advance can on the distributor, or plug it off if you're using manifold vacuum for your advance. Just an observation. I'm sure you'll have it all hooked up once you're ready to turn the key.
:gp: I'm learning a lot from you Lemmy. Sounds like a good method. Better than my free hand adjusting :TU:
As I recall, the third screw, above the bottom two, in the center, is for idle air control. Once the throttle stop is set for 550, the idle air is set to the factory idle speed, in drive. When that is set, set the idle mixture screws for best idle, then lean it, (turn clockwise,) until the idle drops about 10 rpm per screw. Then set the idle air for the correct idle speed in drive. That screw is used to allow the same carb to be used on various 430's, in different vehicles and various emissions trims. As I recall, that idle air screw disappeared in most carbs across the board in '69. In Cliff's posts, he mentions the bypass air system in the q-jet. That screw adjusted the bypass air, without changing air bleeds. It was used to allow the smaller 750 cfm carb to feed the larger 401, 430. It is not well known that the only difference between a 750 cfm unit and the 800-830 cfm unit is the size of the primaries. Since emission controls became the primary issue in '66 in calif. and the remainder of the country in '68, the carb's adjustability was essentially lost. For the record, it is the gov't mandated anti-tampering requirements that made the q-jet so application sensitive, as the adjustability was "mandated" out. Ray
