there is a ( HITATCHI DISTRIBUTORS ) metal vacuum advance diaphragm on some 86-87 models that can be cut open, crimped back together and then you can reference it to boost. actually not welding it would allow you to change the spring rates inside... you need to swap over the spring anyways. There are other diaphargms on the stock carb but I'm weary on the amount of travel they have, some too much some too little. The secondary diaphragm and Vacuum idle diaphragm are the best bet. I believe only one is actually able to be unscrewed... the rest are crimped and sealed.
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