Trouble Starting When Hot - Check the Air Gap

We love our classic bikes, but as most of us know, they can be tricky to maintain—especially if you aren't a full-time mechanic or auto-electrician. Even the most seasoned owners can occasionally overlook a small detail that makes a big difference.

One of our long-term customers recently ran into an issue with his Tri-Spark Classic Twin ignition. He reported that his Triumph T140 was running beautifully until it got hot; once the engine was up to temperature, it simply wouldn't restart until it had cooled back down. Interestingly, the unit passed its self-test perfectly.

The Solution: It's All in the Gap

Steve suggested checking the air gap—the clearance between the rotor and the stator. It turns out the gap was just slightly too wide. Once the adjustment was made, the T140 returned to starting first kick, hot or cold.

Precision Adjustment Options

We know that every vintage engine has its own quirks, and sometimes standard adjustments aren't enough to get that perfect clearance. To make installation easier, we have developed several hardware options to help you dial in your timing:

• Custom Spacer: Specifically designed to adjust your rotor position when the air gap is too wide.

• Longer Rotor: A dedicated Classic Twin rotor for setups where the stator sits further back.

• Shorter Rotor: For those tight builds where the air gap is too small and you need more clearance.

Technical Specifications

To ensure your Tri-Spark ignition performs at its peak, aim for the following measurement:

Need More Help?

The Classic Twin Installation Manual features an extensive troubleshooting section starting on page 10. We always recommend reading through and checking the installation if you have any concerns.  

If you’re struggling to hit that 2mm sweet spot, get in touch! We can help you determine if a spacer or a different rotor length is the right fix for your bike.

Updated April 2026.