it is the normal MC-4 which is much thinner than the original MC-1 that the Avid kit provided. http://www.matcomfg.com/MASTERCYLINDER-idv-3404-5.html Note this cylinder can be shortened by screwing the clevis end down to then meet the same length as the old cylinder, but when screwed down, the threads stick up into the clevis, so I had to grind them down to shorten the rod about 1/2", Then they fit perfectly, s shown in the photo. The thinner cylinders need an external reservoir.
I bought the MC-4 regular length, and rather than send them back for about 1/2" too long, I had to rotate the clevis all the way down to fit the existing brake holes. This made the threaded rod stick up into the clevis where it interfered, so I ground off about 4 of the threads on my grindstone (wrapped in wet cloth to prevent heating all those nice delicate brake seals!) and it fit nicely on my stock MK IV pedals. Here is a photo (yes, I had to tighten the set nut after I took the picture!)
I have over 2 hours on the 670 now, and all looks great. I owe a long tome with performance info, but so far runs great, strong, smooth. No leaks or funny stuff, and Rotax Rick's build looks like a good quality job. Mike Hair's exhaust seems great, it fit well, and runs quietly. In cruise, the 670 seems to be able to be throttled back to low fuel flow, so the RAVE valves seem to work, because when at part throttle, the fuel flow seems to be able to get down to descent levels. I can throttle back to less than 5 GPH, and get about 85 mph. Frankly, I have spent most of my time getting the prop set, and the jets. I am flying from Parowan, UT at 6000 feet and about 30 deg C so the air is pretty thin and the mixture had to be jetted way back. I am running 165 jets, and also leaning a little in cruise with the Hacman. The engine starts and runs great, and here is some really rough performance points at 1000 lbs GW and 7000 feet, 28 deg C, 9800 ft DA. I have a fuel flow gauge to help see what the fuel burn is: 5900 rpm, 5.1 GPH, 76 mph IAS, 88 MPH TAS, 1080 EGT. Then 6200 rpm, 7.1 GPH, 82 mph IAS, 95 mph TAS, 1080 EGT. I will be back home next week, and intend to take a few long performance flights to see steady fuel flow, egt, rpm and flight performance and will publish it all. So far the only negative is that my water temps are up, probably because I had to open the cowl bottom and that disturbed the air flow thru the nostril radiators. I added a belly radiator to help, so the radiator is slowing me a little. I have to block the nostrils and also drop the belly rad in the days to come, so more to report . For the rest of the build, the Highwing LLC gear is a dream (see photo), the landings are solid and track straight ahead, no tendency to wander in yaw. The tail wheel hits slightly first in a genuine three pointer, and the aircraft just has no lift left when I bother to hold the stick way back. It feels really solid and not at all as squirrly as it used to. My new brakes are terrific, I installed the MC-4 skinny cylinders (see photo) that allowed me to drill the new pivot much closer to the pedal so I more than doubled my brake force. I can hold the 670 against the brakes now on the ground to about 6000 rpm!
I have over 2 hours on the 670 now, and all looks great. I owe a long tome with performance info, but so far runs great, strong, smooth and most important, it can be throttled back to low fuel flow, so the RAVE valves seem to work. I can throttle back to less than 5 GPH, and get about 85 mph. I will be back home next week, and intend to take a few long performance flights to see fuel flow, egt, rpm and flight performance and will publish it all. So far the only negative is that my water temps are up, probably because I had to open the cowl bottom and that disturbed the air flow. I added a belly radiator to help. Good luck with your experimental Phase I flying! BTW, if your brakes suck with those fat brake cylinders, Joey and I found a great solution.
I bought two 1/8 NPT brass barbed nipples, and cut a few of the barbs off to shorten them, drilled a 3/8" hole in the top and bottom of the tank, and used permatex fuel tank epoxy to butter the threads and then screwed the nipples in. When set, I added the 1/4" tubing and some clamps, and had a nice gas gauge. And yes, I chewed through the fabric with my teeth, or at least it looks that way! I also show Bear Perkins kit that does the trick, too.
I ran all these numbers when I analyzed the Highwing LLC gear (made by Lowell Fitt for me in December) that I installed. The yellow spring that he provided me is a Danly IEM yellow spring that has 1450 Lb per inch, and compresses fully at 1.78" or 2600 lbs of force. (http://www.danly.com/cgi-bin/itemdisp.pl?item=18528). I don't know what the original red spring shown in the pics is, but the color says it is softer than the yellow, if it is a Danly. Assuming the two gear (Airdale and Highwing LLC) have the same general geometry, the big black spring that Fly-n-Low is using appears to have about 6" of working length till it compresses fully, and if the spring rate is 325 Lb per inch, it will flatten at 1950 lbs. That spring is weaker than the flat yellow one, and will flatten sooner and turn into a hard bar sooner. The original yellow spring flattens at 2600 lbs which equates to a 4 g landing, the black spring (if it is 325 lb/inch) will flatten at less than 3 g's . FYI, a 3 g landing is 8 ft/sec drop, a 4G landing is about 12 ft/sec. If the black spring is 375 lb/in, then it flattens at 2250 lbs, which is 3.5 g, still weaker than the yellow spring Highwing gave me.
At the Top, Mark. Here is a quick drawing, I'll get some photos later. My plane is an Avid, MKIV, so the original pedals are by design low mechanical advantage. Your Kitfox is already sweet in that department, from your photos. Note in the photo of my "new" brakes how much closer the pivot point has moved to the pedal, I have about 2.5 times more leverage and therefore more braking power for the same press of my toe brakes.
I finally gave up on my old Matco fat brake cylinders, and rebuilt my system. I installed the newer, slimmer Matco MC-4 cylinders with an external reservoir, and drilled the brake bellcrank on the pedals much closer to the pedal with a second 3/16" hole about 1" from the brake pedal hinge. as opposed to over 2" in the original config. This now gives me about 2 to 2.5 times the previous mechanical advantage. It took a while to bleed the brakes, I finally used the classic method with clear tube into a bottle and pressing the pedals hard. Now the brakes are excellent, I can hold the aircraft from rolling at 5800 rpm with a 670 engine! To clarify - the old cylinders are too fat to fit closer to the pedal, so the best mechanical advantage is only about 1:1, thus the pressure your feet build is limited. The new slim reservoir cylinder easily sits 1" closer, so with only one hole drilled, I doubled the brake power. I used the Matco reservoir kit, it had all the parts and the compression fittings were easy. The whole refit cost me $270 and 2 hours and now I have excellent brakes.
I just upgraded to Rotax 670 and added a belly radiator. I used an older kitfox one that Edmo sent me, they also sell them on ebay. I ran two U-bolts thru the floor that circled the two diagonal steel members that go from the center of the pedal area out and back to the outer frame. You can see one of them peeking out in the photo. I used a 1.5" x 3" aluminum box, as a mount, cut away to lighten it but also to get access to the bolts. The hose is 1' ID high temp silicone form Amazon, really flexible. It needs to be 2" lower, doing that this week.