Generator converted from propane to natural gas. Was starting fine on gasoline or natural gas but became more of an issue recently. Here's what I have done.

1. Changed spark plug and air filters. It is getting spark.
2. Starts fine on gasoline - open choke and move to run.
3. Won't start on natural gas / connected to meter.
4. Remove air filter and use starting fluid in carb:
A. Will start on NG with no air filter. Put air filter in while running and no problems - keeps running
B. Put starting fluid in carb and put back on air filters before starting. Won't start.
5. At one point, it would start once warm and not be an issue. Now, it won't start warm. Must redo step 4a.

I have replaced natural gas regulator and that doesn't seem to be an issue. Seems like an air intake / fuel issue. Will occasionally backfire trying to start.

Open to ideas to get this more consistent / reliable starting. Any ideas I should try?

If it starts with the air filter off, that would tell me that it is likely a NG supply/too lean issue.

Can you start it on gas, supply NG, and switch it over while running to run on NG without it dying?

What generator do you have? What diameter NG hose are you running, and how long is it? What is the output of your supply regulator? 5-7"WC?

What type of conversion did you do? Did you change the orifice? Was it a dual fuel, and now it is a tri-fuel?

Do you have a way to bleed nat gas into the carb to prime it?

Pretty common problem if converting from dual fuel to tri fuel. The propane and gasoline inputs are on the correct side of the choke, when converting to tri fuel, the nat gas comes in on the side of the carb and is positioned such that the choke is ineffective. You have to use your hand at the air box to choke it for nat gas start, gasoline and propane start with the carb choke as normal.

A more powerful battery (switch to lithium ion) can also help over come nat gas starting issues. Spinning the starter faster can help with ineffective priming and/or choking problems.