Help thread: Junak 905 injection tuning

For Junak 905 injection tuning, make the stock setup healthy before tuning anything. Compression, valve clearance, air filter, plug color, chain/CVT condition and tire pressure all matter before chasing power.

If you can, post a photo of the part, connector, plug color, or dash message. A decent photo can save half a page of wrong assumptions. That is how I would approach Junak 905 injection tuning before spending money.

Does Junak 905 injection tuning usually point to one system, or can it be caused by something completely upstream?

Thomas Spagnoli: workshop approach for Junak 905 injection tuning

For Junak 905 injection tuning, I would slow the job down for ten minutes and make the evidence visible. Guessing feels fast, but it usually makes the repair longer.

1. Make the motorcycle mechanically healthy first: compression, valve clearance, plug, filter, fuel delivery, chain/CVT and brakes.
2. Choose changes that match the use case. City scooter, commuter, trail bike and highway bike need different compromises.
3. Confirm legal and insurance rules before derestriction, ECU work, exhaust changes or power kits.
4. Change one thing at a time and keep the original parts until the result is proven reliable.

Keep the original setup in mind. Many faults appear after a small change, and the change is often more useful than the symptom.

This is also the kind of method I teach in the free Motorcycle Mechanics Course here on the platform: observe, measure, confirm, repair, then test again. It is much easier to solve Junak 905 injection tuning when the process is clear.

If you report back, include the measured values, not only whether it felt better. Numbers make the thread useful for the next rider too.

Good point about documenting the baseline. I took photos before touching anything, which may be my most professional move this week. I like that this turned into a checklist instead of a guessing contest.