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Hello again, still unable to locate source of problem with smooth ignition of the fuel stream. Switch is making and valve is energizing. Rechecked pressure (manifold) and between 3.4/3.5", inspected burner again, pulled vent cap and inspected concentric vent/supply pipe. Did put a couple drops of turbine oil on comb. mtr. bearings on a longshot. When 1st reignition occurs it is smooth and proper, after that the rollout boom is back. (not technically a rollout but aptly describes condition) A local said to put just a smidge more kick in the hsi bracket, not help. What now. Never stumped by the elusive gremlin like this before.
thanks Pat

Some mobile furnaces have a step gas valve. That is it opens for a few seconds at a lower pressure then it comes on full bore. It makes for a smooth proven light off of the main burner. My unit has this feature.

When you say roll out what does this exactly mean. In the heat business roll out means that the flames are coming out of the furnace in the front and I doubt if that is your problem because you have a sealed combustion chamber. So what does your roll out mean or do exactly and why do you feel it is not normal. When some furnaces lite off they will go vroom and the settle down. This is because the initial release of pressure from the gas valve is just a little high.

So what does your unit do exactly?
Why do you feel it is not normal?
What is the name brand and part number of the gas valve that is in your unit.

I am not sure which gas valve is installed in the unit. It is a double solenoid valve(1 towards each end) with the coils opposite each other and the valve on off switch and qd's terminals in the center.
By rollout I am describing the violent initial combustion condition. No the flame is not physically able to roll out, but normal ignition is like turning on a water hose, it ignites rising to full ignition, not like flipping a switch and wham immediate full bore intense initial ignition(actual explosion into combustion as opposed to ramping into it) There are more than 2 terminals on the valve itself but the unit only uses 2 of them. Manifold pressure is just a skosh under 3.5" but over 3.45(use a 0-10"gauge, not 0-35") . What is the normal time out intervals for each component on call for heat. I could locate no actual way to set or vary these delays. In the chip I assume as no capacitors installed on board in a timing circuit configuration.

There are no user serviceable/adjustable timers on the furnace. The circuit board operates as a event control switch. As each process passes the board allows the next process to happen working up to ignition. Since your furnace is operating there should be NO problem with the board. Have you checked the static pressure in the combustion chamber or taken a flue sample for CO concentration?

On the listing label on the furnace it should list the water column specs for gas pressure both in and out during the firing of the furnace.. By any coincidence was this furnace converted from propane to natural gas?

I really would like to have the model and brand of the gas valve. I want to see if it is a step open or if the correct valve is installed.