12A issues and questions
 

Im guessing this is about the 3rd topic about this, from the last month. Im planning on building soon down the road, but until then Im wanting to drive it the way it is. Itll idle ok, but as soon as I go to pull away the noises and problems start. I have noises out the ass, along with vibrations and rattles. I know its not really possible to guess what a problem is on the internet without knowing about the car condition. At idle its ok, a bit rough and lobey sounding, almost like it has a street port (it doesnt) then at low rpm it will spit and sputter and hessitate, then mid rpm range i get a terrible chirping/sqeeling noise. i think ive narrowed it down to maybe alternator (hoping it isnt a bearing or something internal, as i MIGHT rebuild this 12A and down want to have to replace shit). then you get to the higher rpms and begin to hear a knock, id compare the noise to an electric mixers paddles hitting the side of a plastic bowl. Now for the guessing. would you guys guess all of these noises could be external/ accessories and/or fuel setting, ingition timing or something else like that. Or could these be internal, and leaving me with a hole in my wallet?

car has a mikuni carb, untuned, no fpr, rb headers and full exhaust... any guesses thrown my way will be appriciated

My first pass would be to verify the timing and make sure its set correctly. Thsi means make sure the wires are good and plugged into the right connecttions and make sure the distributor is indexed correctly with TDC and your coils are good. Then set the timing to the factory defaults for now.

If its got a mikuni the rough idle and loping can be attributed to a porrly tuned carb or timing. Thats why I would set the timing first. Get the carb tuned so that its running at a good mixture. The sputter and hesitattion is pretty typical for a large two barrel progressive carb like the mikuni but you should be able to tune it away almost completely. I have a Dellorto and had some of these same symptoms over time.

The chirping is probably a belt slipping, especially if the air pump is gone and theres just the one belt for the water pump and alternator. I use a dual pulley setup to fix that, others use a special belt, can't remember the name of it.

The knock at high rpms sounds ominous, but I would sovle the other issues first so that its easier to chase this down.

To rule out external accesories, kick the belts off, and start it up. Obviously, you don't want to let it run very long without the water pump spinning, but a couple minutes would be more than enough to determine if the noises go away or not.

The mid rpm chirping/ squeel is deffinately alternator. so thats taken care of. i kinf of thought the low rpm sputter was just the carb like you said, i need a widebands and fpr i guess to fix that, alone with playing with emultion tubes and jets, ect. and the high rpm im still scared of... not maving much luck figuring it out. do you think maybe a high fuel pressure could cause a knock? or maybe its something in the ignition system. the timing is correct, shot it with a timing light. ill be getting new plugs, wires, dist., coils and some other stuff over time. so i guess ill know eventually. thanks for the help

You need around 4.5 psi fuel pressure.