I heard of a bad coil causing weak spark? Did you do a compression test, you might have a bad valve. How does it idle? Is the linkage set up correclty, when it's floored is the butterfly in the carb all the way open? Any possiblity you have a restriction in the exhaust, clogged Cat or old muffler, bent tubing, bannana in tail pipe? What type of air filter are you running any issues with air flow?

Also since you have a weber are you sure your vac advance on the dizzy is correct?

Just throwing out everything I can think of.

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