I got an email this morning from Stefano. He contacted Elektra to verify the group jet size. All the Elektra OEM group jets are 0.9mm.

I have been looking around for a group jet for some time to no avail. It appears no one has a smaller than stock jet for an Elektra. One major supplier even recommended dropping a stainless wire down the jet to restrict it, not going there.

Being a biker, I had noticed that the Elektra group jet looks to be the same thread and size as the main jet for my Kawasaki"s Kein carbs. Unfortunately, carburetor jets are sized based on the fuel they dispense over time, not by inches or mm"s. So tomorrow I am taking my wire size feeler gauge to the bike store to size out some jets and give them a try.

For those wondering, jets are measured in millimeters and the stock Elektra jets are 0.9mm (0.035 inch). I am looking for a 0.7mm (0.0275 inch) and 0.6mm (0.0236 inch). If I find the right size I will post an update with the correct jet size.

Today I grabbed my wire feeler gauge and headed off to my favorite Kawasaki shop to size out some jets. We managed to find a 68 and 72.5 main jet for a Kein carburetor. My gauge puts the 72.5 between a 0.8mm and 0.7mm. The 68 jet sized between a 0.7mm and 0.6mm so I got one of each. Since these jets are intended for a gas carb I gave them a soak in some JoeGlo to make sure all the manufacturing oils were cleaned off.

Just in case you are wondering, a 0.8mm jet is 0.0315in, 0.7 is 0.0275in, 0.6mm 0.0236in and a 0.5mm is 0.0196inch.

Before I pulled out the stock jet I did a flow test to measure the water debit. With the stock Elektra 0.9mm jet I get 4.225 ounces by weight in 7 seconds with no portafilter. I shut off the water, took the top cap off and removed the jet. I mentioned earlier that the jet screws onto a riser so you may have to hold the riser with a wrench and unscrew the jet from the top of it.

I went with the 68 main jet, perfect fit. I reassembled the group top (one bolt) turned on the water and ran the same test again. I am now flowing the same 4.225 ounces in 9 seconds; I have slowed the flow rate by two seconds. I also put my Scace II on to check pressure. There was no discernable change in brew pressure but the pressure ramp did appear to be slightly slower. When I say slightly, I mean slightly, maybe one second but I did not time the pressure ramp with the stock jet.

Did it make a change in the espresso, maybe? I am running some "past its prime" espresso right now while I wait for a batch of home roast to degas. Initial impression, there is not much difference in the cup but the infusion appears to have slowed slightly, which was the reason for the exercise. I wanted to test out different puck infusion rates. The Elektra is a very forgiving machine to start with and the reduction in the group jet may make it even more so especially for a down dosed 14 gram basket.

In summary, if you want to try different flow rates on your Elektra espresso machine, visit your local Kawasaki (or other motorcycle) dealer and get a 68 main jet for a Kein carburetor. That will put you between a 0.7 and 0.6mm group jet. You could go smaller, I would guess a 62 main jet would put you around 0.5mm if you can find one. These jets are very small so it may be difficult to find them. My ZX6 Ninja runs a 137 main jet so these are getting in the realm of a sub 100cc dirt bike carbs.

The reduced jet, as stated above, has lowered the water debit. A side effect of that is longer cooling flushes. That may sound like a bad thing but it is not. For those that have not used a rotary pump machine, the flow rate is around 3x that of a vibe pump. On my A3, 200F brew temp was two-three seconds past flash boil so getting 201 or 199 could be challenging.

With the reduced flow, I am getting 4 seconds (or a 4 count in my head, I don't use a stopwatch) followed by an immediate lock and pull put me at 200-200.8F. With a 5 count I get a high 199 (say 199.7) to 200.4, a 6 count gets me 199 (198.7-199.4), a 3 count gets me 201. It is making my target temperature much easier and more precise to hit. There is also a slightly longer preinfusion. I have been getting some of the best shots I have ever had from the machine the past couple of days and that was with coffee that was past its prime.

FYI, I pull a long (7-8 second) cooling flush when I walk up to the machine to cool it down before I start my routine which averages less than two minutes from the initial long cooling flush to when I have my portafilter ready and pull the second cooling flush and then lock and pull. The temperatures are gathered using a calibrated ScaceII and Fluke 54II.

Do you mean Keihin carb jets? You could order one from here down to size 60. I'm guessing it would be the 99101-393 series for Kawasaki road bikes.

http://www.motorcyclecarbs.com/Ke..._99101-393_C78.cfm

Hi Dave,

I was curious whether you decided to stick with the smaller gicleur or went back to the original? I'm thinking of reducing the diameter of the gicleur by using a short piece of thin copper wire (a temporary solution), but first I wanted to clarify if it's worth the hassle.

Regards,
dsc.

I left the smaller jet in the machine. Been running it that way for over a year now with no issues, and it is a Keihin carb jet.

Hi Dave,

thanks for the info.

I stuck a 0.5mm dia wire into the jet today which effectively lowered the surface of the jet hole and now it's an equivalent of a 0.75mm dia jet (you can do the math yourself). I checked the brew pressure afterwards and it hasn't changed, so the next thing was to check the water debit. Here's when things get funny:

Before (0.9mm jet): 92ml per 5s

Now (0.9mm jet with a 0.5 wire stuck in it, equ. of a 0.75mm jet): 48ml per 5s

The only difference is that the Before test was done on a cold machine, but I'm guessing that the difference can't be more than 5%.

I'm waiting for the machine to heat up and will report back from the tasting field.

Regards,
dsc.

I'm no expert at fluid dynamics, but it seems like water would be unlikely to flow out of a crescent shaped orifice at the same rate as a round orifice with the same surface area. Maybe I'm totally wrong about that; it's mostly my intuition from poorly remembered high school and college math/physics.

Still, my intuition appears to be backed by the variation between Dave's flow rate delta and your own, as I think that the jet area on each of your setups is pretty close.

Hi Nicholas,

I agree that the flow might be a bit different, but still it shouldn't affect the amount of water, don't you think? Looking at the passage of water through the wire plugged hole in macro mode would probably show chaos, but it's the surface that counts in my opinion. Of course I might be wrong here so feel free to jump in and smack me:)

I had two shots with the smaller jet, one with a 3s inline preinfusion (which bumps the PF mounted pressure gauge to 6bar even though the inline pressure is lower than 1bar - don't know why) and one with no inline preinfusion. The grind was a bit off, so the pours weren't perfect, but with 13.5g in a double basket I got two very nice, quite sweet espressos with no bitterness at all, although lacking a bit in the body department.

Still, my intuition appears to be backed by the variation between Dave's flow rate delta and your own, as I think that the jet area on each of your setups is pretty close.

I agree here as well, the difference is quite big.

Regards,
dsc.