I have a 2016 Multiquip DCA-25SSIU4F Mobile Generator with almost 10,000 hours. It has an Isuzu Engine Model BZ-4LE2T. The unit starts and runs poorly for 15 to 30 seconds before stopping. If I disconnect the muffler system, the engine will run continuously, first with heavy black and then with a lot of white smoke after 2 minutes at 1800 RPM. It sounds OK when running, no missing, but the output of 120 volts is weak at 110 volts and a 1500 watt heat gun barely runs – very low heat and fan speed. I have not tested the 3 phase aspect of the generator. I do not think the generator aspect of the unit is the problem. I think the engine is the issue, but not sure where to look and isolate issues. I am not much of a diesel mechanic; I am mostly a carpenter, but very mechanical and willing to learn. I need to fix this machine in order to run my 3 phase sawmill. I would appreciate any and all help in trouble shooting and fixing this very finely made machine. Everything about this machine seems top quality and worthy of repair. Please advise me where to look and test what the problem is? Thanks for any helpful information - Best regards.