That's not a bad thing at all. When I say I try not to exceed 400 that is my stopping point where I will either ease off or shut down. Thankfully my Phantom has been doing ok so far just cruising along. I have come close pulling a long hill on a hot day though but I also have my fueling intentionally on the rich side to help combat the heat.I am feeling much better about my temps. I've barely hit 300's...
As far as tachometers go you would be using an inductance style of tach where a wire is wrapped around the spark plug lead and the unit itself is usually battery operated. They use common button style batteries in most instances.
I am currently using this unit for tach and temp https://www.amazon.com/Runleader-Te...ps,119&sr=8-22-spons&smid=A3H26M0OO8MHA9&th=1
It's worked well for me so far but some people have complained about some quality/reliability issues. The thermocouple for the head temp is designed to go under the spark plug but that proved a bit tricky with the way the phantom is designed so I have been running it under one of the head nuts with a fender washer to hold it down better. It's going to read a bit cooler there but it still functions well enough to give me an idea of how hot the motor is running. My infared thermometer shows about a 10-15 degree difference between the two locations so I adjust accordingly (390 is actually 400ish).
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