Stumble with rebuilt Thermoquad /340

There is no way in the world a Thermoquad can be adjusted to run perfectly without being on a running engine where it can be adjusted for that particular engine. And I mean NO WAY. It's the luck of the draw if you buy one or have one built and it bolts on and runs good.

Here is what "I" would check first from what you describe.

Remove the air cleaner. Start the engine and warm it up. Take your finger and very gently try to push the secondary air door open.

If you can push it open any at all very easily and then it gets hard to push open, the secondary dashpot control rod needs to be bent so that that "slack" is removed.

You should not be able to push the secondary air door open AT ALL with the engine running without IMMEDIATELY fighting against the secondary pulloff. Don't go too far and tighten it up too much. Just bend the rod JUST enough so the slack is taken out.

Check that BEFORE making a change to the secondary air door spring tension. Usually, that's what's wrong.

If the air door is tightly pulled closed when running and there is no free slack, then you probably need to adjust the secondary air door spring tighter.

Check on the slack first and report back.