Water Heater UPDATE 3

Likely only one valve but with two coils, needing to have both coils energized to open the valve, some sort of safety system?

Maybe carb cleaner or brake parts cleaner, something you know will evaporate and not leave any residues?

I have never found the need to clean out the gas valve in my many years of service. I replace valves because they either work or they don't due to bad solenoid coils or defective valve.
These are not meant to be serviceable and I wouldn't use mineral spirits.

Ex-Tech wrote:
I have never found the need to clean out the gas valve in my many years of service. I replace valves because they either work or they don't due to bad solenoid coils or defective valve.
These are not meant to be serviceable and I wouldn't use mineral spirits.

I see in the manual linked in the OP now, that my problem might be outside the valve part maybe air amount. The flame runs ok and then goes into spasms and then runs well again keeps happening for the whole time when burner on, but it all keeps going.

I have used mineral spirits to clean orifices etc with success, so I thought it would work with this too. What would you clean the pipes and orifices out with?

I would not use anything inside the valve.
Have you measured resistance on the two valve coils. They should read the same or close to it.
Have you cleaned out the burner tube between the orifice and the tank? I have used a shotgun cleaning brush to clean mine.

As Bud said, check the burner tube, also make sure the valve is aimed straight down the tube. The older models would get way out of line, and bending of the valve bracket was needed.

enblethen wrote:
I would not use anything inside the valve.
Have you measured resistance on the two valve coils. They should read the same or close to it.
Have you cleaned out the burner tube between the orifice and the tank? I have used a shotgun cleaning brush to clean mine.

I have a copy of the service manual now from that link to take out there and try things. I did clean the orifice and tubes.

Had another look at it. Fired right up no problem, but it is doing "that thing" still.

-The alignment looks good.

-The dime shaped flame spreader was not quite parallel and the end of the tube there is rusty raggedy. I clumsily broke off the dime shaped deflector disk trying to bend it down a bit. This did not seem to make any difference to the flame after that thank goodness.

The adjustable air shutter at the orifice end is more like half open instead of 1/4 the way. Rusted in place.

So the thing it is doing-- It burns nicely for few seconds not much noise at the water heater end, then back at the orifice and air shutter holes, it starts making a loud "Tshhhh" hissing blow- torchy burbley sort of noise and an intermittent bit of flame comes out the air shutter holes (very little). The main flame keeps going at the water heater end, but seems disturbed (hard to describe)when this all happens.

The "event" stops after a few seconds and after some more seconds it starts again(longer time with no event than the time the event takes) The times it happens varies and how long the event lasts each time varies. This will continue until the water is hot and it all stops about 45 minutes later

That is why I thought there might be something in the gas valve "block thing" that was loose debris or whatever that I could clean out of there.

I’d replace the burner tube. Without the flame spreader, the unit doesn’t heat very well, and the shutter is likely open too far. Atwood should not roar when burning (Suburbans do roar). I close the shutter, then open until it just starts to roar. Closing the door will quiet it down.

Thanks! Ok I tried to cover the air shutter more using a hose clamp like this, and it worked! :) I left a little open part.

The "event" did not happen at all. The burner is very quiet.

The flame in the water heater end might not be right though. It starts off light blue but then mostly has a long tongue of yellow flame going all the way in the big tube and around a corner. Just have to see how long it takes to get the water hot next time we use it.

https://www.canadiantire.ca/en/pdp/plumbshop-gear-clamp-0632141p.0632141.html?gclid=EAIaIQobChMI99_b0PyT4AIV-SCtBh2psgzqEAQYASABEgLPMvD_BwE&gclsrc=aw.ds#store=366

EDIT--I ordered a new burner, arrives next week.

https://www.amazon.com/Atwood-91638-Main-Burner/dp/B004QMXSXY/ref=sr_1_37?ie=UTF8&qid=1548807628&sr=8-37&keywords=atwood+rv+water+heater+parts

New burner arrived and installed. The amazon info and bag it came in all said Part 91638 Main Burner, but the Dometic paper in the bag said Part 91629 Main Burner Replacement, with a drawing showing the pilot light version of the heater. (my heater is with no pilot)

Anyway it turned out to be the same, so it went on ok. Flame with no noise and better shape with the flame spreader on it than without. :)