OldBMW- if it won't simmer, it needs servicing - as something isn't right- mine does beautifully-
If it's this one you have, (same as mine) you simply change the jet for the gas-
Jet number 45 is for gas, 37 gasoline/whitegas and 28 for diesel/kerosene.
It is a very good stove and should you run out of gas but have your bike, you won't be stuck for a brew-up

servicing? the thing is new. will not simmer slowly. I know about the jets, but why use it as a clumsy gaz stove when my £10 wonder is 10 time better? Incidentally I started using it on kerosene and thought that poor. in fact it works better on kero than anything else
trying to cook my first curry it went out as i tried to lower the flame, the heat exchanger is just too small to work at low throttle openings. I had to switch to the gaz stove to finish cooking our supper in the snowy Pyrenees.

Will probably buy another gaz stove as it takes up no more room than the fuel bottle and that means i can deploy two cookers at once if needed. Without leaking as i connect or disconnect the fuel. ( I leave the gaz canister permanently connected).

Oldbmw , "Why use it as a clumsy gas stove?" ermm well I don't consider it clumsy- it roars or whispers whichever fuel I use and give me maximum choice of fuels-" Diesel isn't quite 'as nice' to cook with but works fine-
I am guessing that the fuel filter in yours is blocked / partly perished -it's a really tiny white part- look in the pictures- that would probably account for it not simmering.
Without wishing to come across as a clever-clogs - it may help if you are shown how to use it- Last biker I met in southern Morocco was about to chuck his away in the bin in complete frustration- when I cleaned it and showed him 'how-to' he was the happiest bunny on the prairie and was amazed how brilliantly his stove really was- (btw- I hated mine until I was shown how-to as well!)

When I go further afield and rely on petrol & I use the Optimus Nova stove- which uses a QD to the fuel bottle (no more leaks on disconnection -see pic)- they both need pre-heat -which takes no time at all- but are very strong cookers and quite small weight.

Below is the Nova- with saelf cleaning needle operated by a magnet-clever- reducing field cleaning massively-
Tip- if anyone wants to buy the Nova PLUS- consider this- I had one and the fuel pipe is the simmer / full burn control- Because of its curved shape it is a real nuisance to operate so I sold it- picture below is the standard Nova with foldaway handle which a solid and reliable piece of kit-
My 2 pence!
Oldbmw, if you ever swing by Kent, bring it round & I'll try to fix it for you- I've cooked many a tasty meal on that cooker and still do! would be a shame to dump it-