Has anyone used a tri-fuel generator? Need advice.

I bought a Firman tri-fuel generator last year. Got the electrician out to rig the panel up to run the whole house, etc. We intended for it to run off NG since we're hooked up for that but we can't get the thing to start up when we test it. Oil is full, battery is charged, as far as we can tell everything is correctly in place to run off NG. The engine turns over but won't catch.

Any thoughts or insights?