BernieDawg reviewed the previous, flawed Primus Gravity MF here: https://classiccampstoves.com/threads/13168 This is a review of the replacement model, the Gravity II MF, running on Coleman Fuel and on Kerosene. This is a stove in the modern sense, a burner, flex line, fuel bottle with pump unit. It came with a nice little stuff sack, a multi-tool with pricker, jets for gas, petrol and kero and an alu wind shield. It's a silent burner design, low mounted with rather spindly looking stainless steel legs (x4), and the Primus ergo pump unit. The stove can burn cannister gas, naptha, gasoline and kerosene. I've used a 1L primus bottle and tested with Coleman fuel and Kerosene On unpacking the stove, my first thought was that the stove legs and pot stand seem weak. It has, however, had no difficulties holding rather large pots, and shows little flex. I'd avoid stepping on it, though. The jet is relatively straight-forward to change, simply unscrew the retaining collar on the generator, then unscrew and replace the appropriate jet. I used the white gas (middle-size) jet. A priming pad is mounted in a small tray beneath the air intake and generator. It looks like an afterthought. Here, the spindly burner supports 5.5kg of lead crucible without any flex noted: The hose is nice, quite flexible, small diameter, with a control valve and threaded connector on the end. The connector fits the pump or threaded gas cannisters without adaptors. Nice. The pump assembly seems well made, and is serviceable without tools. That's nice. The pump itself is aluminum, there's a brass fuel pickup alongside, and a plastic bottle-thread to mount it all in. The NRV is plastic, bayonet assembled, serviceable by hand. Nice. The wind shield is just a folded sheet of aluminum, very crude. I avoid folding it again by wrapping it around the fuel bottle for packing. A 2 or 3 hinged unit would be so much nicer. Folding this will crack it in time, 'tis the nature of aluminum. The instructions suck. Much lawyer, and little actual instruction. I'd hate to be a newbie with his first liquid fuel stove.... But it operates like about any european petrol stove. I filled my fuel bottle to the fill line with Coleman fuel and installed the pump, then threaded on the fuel line to the burner. Everything sealed nicely. I added about 20 pumps to pressurize the fuel bottle, then cracked the fuel control to add some priming fuel to the priming pad. Once fuel showed at the pad, I shut it off, and struck my match. The prime lit and burned vigourously for a minute or so, with the stove beginning to sputter after maybe 20 seconds. This is very easy to over-prime on white gas. The underside of the burner was coated with soot. Priming: As the prime burnt down, open the fuel valve and the burner comes to life, orange flame at first, clearing to blue as the remains of the prime burn out and quit robbing the O2. The flame was very well distributed, unlike what has been reported for the original Gravity. This is the Gravity II model, seemlingly a "bug fix" for the original. The flame pattern is very much like that of a classic Coleman "band-o-blue" burner. Finishing prime: Band-o-blue: The burner puts out gobs of heat if you pump the pressure up well, and can be turned back to maybe 25% of full power on liquid fuel. Not quite a simmer, perhaps, but a decent range of control. I was able to reheat frozen soup for Christmas lunch on it without significant burning-on, so not bad really. Reportedly, the simmer is better on cannister gas, but I hate cannister gas, LOL. Simmer flame: Full Bore Flame: After getting used to the operation of the stove, I tried a couple water boil tests. Primus claims 40 sec preheat, 4 minutes to boil 1L. The best I've achieved was 75 second preheat (it's easy to overprime, you see!), and 4 minute, 15 seconds to boil in my MSR Cascade SS medium size pot, and I'd call that pretty handy. Shutting down the stove is nice. Flipping the fuel bottle over 180 degrees puts the fuel pickup in the bottle's airspace, and you allow the remaining fuel in the line to burn off. The flame ghosts then goes out, and you shut the valve. The line and burner are thus quite dry for packing, and this is GREAT. Be sure to depressurize the fuel bottle before disconnecting the fuel line to avoid some drips before the connector is fully detached. Ultimately, I am coming to like this stove. It's fairly well-mannered and versatile. I'd have liked to see a more stout leg design, perhaps joined beneath as well as on top of the burner. That's really my biggest beef with it. A local burner valve might improve simmer control, like in the Omnifuel. As-is, this is a powerful, lightweight, QUIET and versatile stove. Kerosene running to follow.... J
Now to try on Kerosene.... I should be telling y'all that first, I unscrewed the jet retaining ring from the venturi, and replaced the midsized jet (naptha) with the small kero jet. But I forgot, and just bunged on a bottle of kero, filled the primer tray with meths, set light and let'er rip. Predictably, I had a large orange-rich, though smoke-free flame. I flipped the fuel bottle to purge the stove, let it cool and changed the jet. A dab of anti-seize on the retaining ring eases things greatly. So, with the right jet installed, I primed with methanol again. After a minute and a half, as the prime died down, I opened the fuel valve slightly. After 10 seconds (for the line to fill), the flame burst to life. Despite the fuel bottle being 2/3rds full, the kero required much more pumping for good power. On naptha, 30 pumps gave decent power, with practical full power at around 80. Kero was just idling with 30 pumps, so I added another 90, for 120 pumps. The flame was sill much smaller than the naphta flame, but the simmer was much better. The flame was very clean, but for the occasional streak. The simmer on kerosene is impressive. Very low simmer was possible, and far more stable than the naptha simmer. I did note, however, that the burner itself glows during simmering. The impression is that the kero jet is slightly small for the best mixture. It feels lean. Back to full blast, and a few more pumps. I put the medium MSR Cascade stainless pot on with 1L of 6C cold water in it on the stove, started the timer, and placed the heat reflector/windshield around the stove. A peak thru the windscreen at the flame working along inside: Gratuitous flame shot: Ultimately, the stove is much less potent on kerosene. The pot rolled to a boil about 7 minutes after meeting flame, compared to 4:15 with naptha under otherwise similar conditions. So, there it is. The Gravity II MF works well with naptha, and works reasonably with kero. Simmering ability is very good with kero, and moderate with naptha. The power is reasonable on kero, and quite good with naptha. J
Comprehensive review there Jason - though I don't share your dislike of canister gas. My compliments. Without the insights you've provided I'd have supposed that a 'Mark II' wouldn't have been much of an improvement on such a poor Mark I. John
Well, I finally picked up a cannister of mixed propane/butane this weekend, to test the Gravity II MF on canister gas. This is what's available at the local store: http://www.canadiantire.ca/AST/browse/5/SportsRec/Camping/CampingStovesAppliances/PRDOVR~0762010P/Butane%2BPropane+Mixed+Fuel.jsp?locale=en I didn't take any pictures, they'd look substantially the same as it burning other fuels. The stove ran very well on canister gas, from the lowest simmer to a very impressive full-bore flame, always clean blue. I used the cannister in gas feed mode, but it accepted a liquid feed just as readily, though without the precise flame control Boil time on canister gas was 4:05, at least the equal of the stove on Coleman fuel. Couldn't help but think that it seemed a bit soul-less and boringly incantation-free on the canister... But it seemed a nice trick for convenient brew-ups on a shorter hike. J
