Waste Oil Heater Forum - Your definitive source for burning waste oil for heat.

I was burning used oil from diesel trucks and equipment and it burned very well with almost no problems. I switched over to oil from a Harley shop and now having trouble with it igniting. If i turn the air pressure down, i can get it to ignite and after it runs a few minutes, can turn pressure back up to 12psi and it will stay running. Next time it tries to fire, it wont go and go through the process again. I have put some diesel fuel in the oil to cut it, but doesnt seem to help. Ideas? Thanks in advance.