Help thread: NC750X aftermarket exhaust runs lean

For NC750X aftermarket exhaust runs lean, I would do a visual inspection first. Heat marks, loose grounds, cheap adapters, bad crimps and tired clamps explain a shocking number of problems.

I learned this the boring way: do one test, write the result down, then move on. Five changes at once only tells you that one of five things mattered. That is how I would approach NC750X aftermarket exhaust runs lean before spending money.

Thomas Spagnoli: workshop approach for NC750X aftermarket exhaust runs lean

I would treat NC750X aftermarket exhaust runs lean as a diagnosis, not as a shopping list. The first job is to turn a vague complaint into a repeatable test.

1. Inspect the physical installation first: clamps, brackets, heat shields, routing, grounds, fuses, and connector strain.
2. Measure voltage drop under load on electrical faults; for exhaust faults, listen for leaks at the head and joints.
3. Do not ignore heat. Melted plastic, brown terminals, blue pipe sections, and cooked insulation are evidence.
4. After any repair, test hot and cold. Many electrical/exhaust issues behave differently once everything expands.

Do not let forum confidence replace measurement. If two possible causes fit NC750X aftermarket exhaust runs lean, choose the one you can test cleanly first.

The free Motorcycle Mechanics Course on this site goes through this exact thinking: electrical checks, fuel checks, mechanical baseline, diagnostic flow and safe habits. It will help you approach NC750X aftermarket exhaust runs lean with less guessing.

Post the machine model, year, mileage and one clear symptom, and I would choose the next test from there.

If the bike runs fine most of the time, would you still replace parts, or keep riding with a notebook and test plan?

I am going to do the boring checks first. Annoyingly, the boring checks are starting to sound like the correct checks. At least now I know what I am trying to prove before spending money.