Exhaust Gas Temp
Diagnostics
A thermocouple clamped in each header pipe, the dongle reading both, and this pair of gauges on your phone. EGT is the per-cylinder truth-teller: it shows lean and rich for each cylinder separately, which a single tailpipe sensor can never do. Work the mixture trims and watch each cylinder answer on its own gauge.
Richer runs cooler, leaner runs hotter — up to the peak. Past peak-EGT lean, the charge starts misfiring and the gauge falls while the engine runs worse. Hot-and-rough is leaner than hot-and-clean.
Hear the diagnostic described
Running it live — with your dongle
The dongle is paired, EGT 1 is in the front pipe, EGT 2 is in the rear, and the two gauges on this page are your two cylinders' exhaust temperatures, live. This is what running the EGT diagnostic on the real bike looks like.
One gauge tells you about mixture. Two gauges tell you about balance, and balance is where the interesting problems live.
Start the engine and give the probes a minute to heat-soak. Cold probes read nonsense, and a blip of throttle reads almost nothing either, because the probe needs a few seconds of steady running to catch up with the gas passing it. EGT is a steady-state tool. Hold a condition, let it settle, then believe the number.
Ride or hold the bike at a steady cruise and read the pair together. A healthy cruise lives somewhere around a thousand fifty to twelve hundred fifty degrees on each cylinder. The split between them is the headline: under about fifty degrees apart at steady cruise is a balanced engine. Do not chase the rear cylinder for running a touch hotter; on an air-cooled twin it breathes the front cylinder's heated air, and a small offset is its birthright.
A split that grows past seventy-five to a hundred degrees is one cylinder asking for attention on its own: its intake seal leaking, its share of the fueling off, its plug or valves unhappy. Both gauges climbing together is a different picture entirely: that is fueling drifting lean for the whole engine, one carb feeding both sides. Moving one number is what a fault does. Moving both is what a jetting change does. Learning to tell those two pictures apart is most of what this tool teaches.
And respect the line at the top of the gauges: fourteen hundred degrees is lean-danger territory, the heat that hurts parts. If a cylinder walks toward it under load, richen or back off first and diagnose second. Read the pair at steady cruise, watch the split, mind the line, and these two little numbers will catch a developing leak weeks before it ever strands you.
How this page works
Welcome to the EGT page. EGT stands for exhaust gas temperature.
Let me describe the diagnostic, and then this page.
Every cylinder burns its own fire, and the temperature of the exhaust leaving it is a thermometer stuck into that fire. Lean mixtures burn hot; rich mixtures burn cooler. So a probe in each header pipe tells you, cylinder by cylinder, where the mixture stands. One probe tells you about fueling. Two probes tell you something subtler and more valuable: balance. When one cylinder's number moves and the other's does not, the cause lives in that cylinder: its intake seal, its plug, its share of the fueling. When both move together, the cause is global: the jetting, the fuel, the whole engine breathing differently. Almost every exhaust-temperature mystery is one of those two pictures, and this page is built to show you which one you are looking at.
The top of the page holds the pair of gauges: EGT 1, the front cylinder's header probe, and EGT 2, the rear's, each with its own big number. Between them, the page does the arithmetic for you: the cylinder-to-cylinder split, how far apart the two are running, with the guidance written out. Under about fifty degrees apart at a steady cruise is a balanced engine. The rear jug on an air-cooled twin normally runs a touch hotter, breathing the front cylinder's heated air; that small offset is normal and not worth chasing. A split growing past seventy-five to a hundred degrees is a cylinder asking for attention.
A guidance box reads the pair together and names the move: both hot, both cool, or one split from the other, and which jetting change or fault to chase. The throttle control below walks the pair through the zones, idle, cruise, and wide open, because exhaust temperature climbs with load, and the number that matters most is the one held wide open, not the one on a blip. Read these gauges under steady load and give every change a few seconds; the probe has to heat-soak before it tells the truth.
The Mixture section gives each cylinder its own trim, a teaching control that stands in for that cylinder's whole fueling story. Drag one toward lean and watch that gauge climb; drag it toward rich and watch it cool. On the real bike, one carb feeds both cylinders, so a jet change moves both trims together, and that is exactly the lesson: learn to tell a one-cylinder picture from a both-cylinder picture and these gauges have done their job. There is also an intake-leak switch for the rear cylinder, the classic one-cylinder fault, there for you to recognize forever once you have seen what it does to the split.
The live trace draws the last twelve seconds of both probes against the lean-danger line at fourteen hundred degrees, the heat that hurts parts. Above that, the Ride Monitor and Trends sections are Premium's layer: the monitor watches both cylinders for a whole ride and alerts the moment one enters the danger zone, and Trends plots each cylinder's cruise temperature across your saved sessions, because a slow one-cylinder climb is the signature of a leak developing weeks before it would ever show up as an alert on a ride.
Stuck mid-procedure? The written steps and the voice can only take you so far. Ask for help and a person will help you get through it.
Ask for helpSome problems run deeper than this page can take you. When one does, the next step is the members page, where the Pesky Throttle family digs in together. Joining is free: no dongle to buy, nothing to subscribe to. The value is the members themselves, collaborating and sharing what they know, and that is often worth more than the product itself. Joining just makes more sense than not joining.
Go to the members pageInstructions and how-tos: see below the diagnostic tool.
Start the engine and let the probes heat-soak — EGT means nothing until the pipes are up to temp.
Front cylinder
Rear cylinder
Once both probes are hot, this box reads the pair of gauges together — both hot, both cool, or one split from the other — and names the jetting move or the fault to chase.
EGT climbs with load. The same mixture that's fine at cruise can run into the red held wide open — that's why the danger line matters most in the wide-open zone, and why you read these gauges under a steady load, not on a blip.
Your settings are saved on this device — no account needed.
Mixture — per cylinder
Each trim stands in for that cylinder's fueling: its share of the carb circuits, its intake seal, its plug and valve health, all rolled into one dial. Drag toward lean and watch that cylinder's gauge climb; drag toward rich and watch it cool. In the real world you'd make these moves with jets and the mixture screw for both cylinders together — the per-cylinder trim here is how you learn what each gauge is telling you.
Front cylinder mixture
The front jug gets clean cooling air, so a healthy front cylinder is your reference gauge.
Rear cylinder mixture
The rear jug runs in heated air off the front one, so a small positive offset is normal — a big one is not.
Moving both trims together is what a jet change does — one carb feeds both cylinders. Moving one is what a fault does. Learn to tell those two pictures apart and the gauges have done their job.
Live trace
Last 12 seconds of both probes against the lean-danger line. Watch how the gauges lag a throttle change — the probe has to heat-soak, so give every jetting change a few seconds of steady running before you believe the number.
Temperature card
| Front EGT | — |
| Rear EGT | — |
| Split | — |
| Front trim | 0 |
| Rear trim | 0 |
| Rear intake leak | None |
On your conversion the rear cylinder is the one to watch: it runs hotter by design, and it's the far end of the 2-into-1 manifold — if the split ever grows on the real bike, the rear flange seal and the manifold joint on that side are the first places to spray-check, before you touch a jet.
About this reading
Reading EGT by zone
| Zone | Typical | What it means |
|---|---|---|
| Idle | 700–1,000 °F | Low load, low temps. Mostly useful for spotting a dead or drowning cylinder — one gauge far below the other at idle is a cylinder not firing clean. |
| Cruise | 1,050–1,250 °F | The tuning zone. Steady-state cruise is where you compare cylinders and judge the needle. Split matters more than the absolute number. |
| Wide open | 1,200–1,350 °F | Peak load. Brief runs to the top of this band are normal on a hard pull; living there is not. |
| Danger | 1,400 °F + | Sustained temps at or past the red line mean a lean cylinder is cooking itself — piston crowns, exhaust valves, and plug electrodes pay for it. Back off and richen. |
Absolute EGT numbers move with probe placement — a probe 2″ from the exhaust port reads hotter than one at 6″. That's why the split and the change from your baseline are the trustworthy signals, not any single number off a chart.
Reading the pair
| Matched, in range | Balanced. Both cylinders fueling alike. Whatever the AFR says, it says it about both. Move on. |
| Both hot together | Global lean. A jetting problem — the circuit for the zone you're in is small. Richen that circuit and both gauges should fall together. |
| Both cool together | Global rich. Safe but soft. Lean the circuit for the zone one step and watch both gauges rise toward the band. |
| One hot, one normal | A cylinder fault, not a jet. The hot cylinder is lean on its own: intake/flange leak on that side, a partially blocked passage, a failing plug. Jets move both — don't chase a one-cylinder split with jetting. |
| One cold, one normal | The cold cylinder isn't working. Rich to the point of misfire, a dead plug, or a valve not sealing. EGT falls because the fire is weak, not because the mixture is right. |
How to use this tool
How an EGT check goes
- Probes in both headers, same distance from each exhaust port, dongle clipped on, phone on the bars. Matched placement is what makes the split honest.
- Warm it up fully and ride a few minutes — cold pipes read low and lie about the split.
- Hold a steady cruise and read both gauges. Write down the pair and the split before changing anything: that's your baseline.
- Split first, jets second. If one cylinder is off on its own, find the mechanical cause — spray-check that side's flange and manifold joint — before any jet comes out.
- Then tune the pair together with the AFR workflow: pilot/screw at idle, needle at cruise, main at wide open, checking that both EGTs stay under the red line as you go.
- On the dyno, EGT is the guardrail: AFR says where the average mixture is, EGT says neither cylinder crosses into the danger zone while you chase it.