Does anyone have an Optimus 8R or 99 or something similar? I have an Optimus 99 that I've just got. I replaced the rubber gasket on the fuel cap, and the stove seems to work well--except for one problem. It looks like there's some vapor escaping from the small hole (with a 5-sided wrench opening) on top of the fuel cap. A little flame flickers there when I run the stove. Can anyone tell me what the problem might be? I'm stumped. I don't know what that opening, which seems to operate some sort of valve, is for, or what's open and what's closed.

That is the pressure safety valve. If the tank has too much pressure, it will vent excess pressure, sometimes with a ball of flame. A spring pushes a rubber seal inside. Sounds like your rubber seal is shot. I bet Butthead has a source!

I suppose I should check first to make sure the valve is closed. That would be clockwise to close it?

Can confirm it is the safety valve, can't help with tightening direction.
If in doubt I would replace the cap, not expensive. I do remember that if you have to replace the cap there are (or used to be) two types. One that worked with a little pump to aid with cold weather starts and one that didn't.
Great little stove mine is going strong, still use it, after almost 50 years.

I have found that if you have a larger pot on it and running on higher setting there is a tendency for the value to open, it should close once the tank cools and pressure drops.

overland: "I suppose I should check first to make sure the valve is closed. That would be clockwise to close it? "

I don't think you can tighten it-it is spring loaded. The "nut" is to gain access for rebuilding (and construction). Replacing the cap is easiest.

The problem is with the one way check valve in the pressurized cap. My old cap, long gone, was just a cap. I installed the cap like you are talking about to use with the tiny pump.

you have a leaking over pressure valve. if it is salvagable, just take a number 2 pencila nd use the friction of the eraser to tighten it down. they are all over the place on ebay. or you can go over to classic camp stoves and buy a pipet or valve from someone.


i would just tighten it all the way up, just not with torq. i run my scea 123 all the way in. if your not using a handpump or dumping gallons of fuel , to prime it. i think your fine. i think it is near impossible to over pressure one of those stoves. if you have it lit, you are constantly releasing pressure anyways. maybe if the stove is off and a forest fire burned up to it, it could go over pressure. but i believe it was designed by a lawyer and you dont need it.

In fact, I noticed that vapor is leaking not only from the valve on the fuel cap but from the line that runs from the fuel tank to the burner. At least I see small flames down there. Am I imaging things or is there another seal there that needs to be attended to?

NEW - Improved ~ ENHANCED "PREMIUM REBUILD KIT" - OPTIMUS 8, 8R, & 99 STOVES

Not a fan of these other than as mantle pieces but Ebay is a good source.
One sugestion, do not fill the tank, leave some space for expansion.

butthead

without playing with it, i think you just need to go to home depot and get a package of graphite valve packing. its like a thick thread. its in the sink section. unscrew the nut and add a couple wraps , then tighten down the nut , be gentle.

or its just the nuts loose from someone tinkering with it.



packing