old wall furnace problem

[cat1947]

Maybe someone can help me. I have an old wall furnace, that when it first lights it seems to have a delayed ignition, Pops when it lights. It doesn't seem to do it as much after the exhaust vent is warmed up. I have removed the burners and cleaned them. They did have some white ash on them, but not much. The pilot is plenty big enough with the flames going right over one of the slots in the middle of the burners. I am at a loss as what to do next. This furnace is on natural gas.
Any thoughts would be appriecated.
Thanks
Andy

[HeyBob]

Andy,

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