Why furnace has a small puff of flame at the gas nozzle/orifice during ignition?

[michael77]

I have a ICG/Keeprite furnace #HCA090L, high efficiency, mfg 1984, input 90 btu, output 83.7 btu.

The furnace is still operating just fine but I am noticing a small puff of flame at the gas
nozzle/orifice centered at the opening of the main burner shaft during ignition making a popping sound,

the flame lasts 2 seconds....this puff of flame is not present after the main burner ignites....The gas
nozzle/orifice is centered at the opening of the long 2-3" dia. round burner shaft...There is only one main

long burner with a cap spreader type of orifice on the main flame end of the burner....I am suspecting the
pipe dope around the gas nozzle/orifice has dried up thru time...I will try to re-dope the fitting of the

gas nozzle/orifice....but also could this be a leaking solenoid gas valve?....Was ICG/Keeprite mfg
under another name as I am having difficulty finding manuals and parts for this furnace?....Any info,

suggestions would be appreciated...thanks

[Admin]

Is this furnace on propane or natural gas?

[michael77]

Furnace is natural gas

[Admin]

Does this furnace have a constant pilot, or is it spark or hot surface ignition?

What you're describing is called flashback.  If there's a primary air adjustment on the burner I would try closing it slightly to reduce the primary air mixing with the gas.  Otherwise you may have a faulty gas valve that could be leaking gas.  If you have spark ignition, the module should energize the gas valve PV terminal and only the pilot light should be burning.  Then the MV terminal is energized and the burner should ignite.  A faulty gas valve could let a little gas leak out to the main burner when the pilot is lighting.  

Try disconnecting the MV wire on the gas valve and restart the furnace in heating.  If you continue to get flashback when the pilot is lighting, and the MV wire is disconnected, a bad gas valve is the most likely cause.

[michael77]

Thanks for getting back with suggestions....It has spark ignition......I will try adjusting primary air,  next will try disconnecting the MV wire on the gas valve and restart the furnace in heating......Will report back to forum....thanks again for your help....