facthunter Posted January 28, 2023 Share Posted January 28, 2023 I could be a commutator for your armature but that might generate some Tension that could be terminal to the discourse.. Nev 1 1 Link to comment Share on other sites More sharing options...
pluessy Posted January 28, 2023 Share Posted January 28, 2023 no need, the #35 (0.35mm) jet has been documented by Rotax and mentioned a few times in this thread. 1 2 Link to comment Share on other sites More sharing options...
skippydiesel Posted January 28, 2023 Author Share Posted January 28, 2023 (edited) 2 hours ago, pluessy said: no need, the #35 (0.35mm) jet has been documented by Rotax and mentioned a few times in this thread. Unless Rotax have changed their part, the jet supplied to me on the 25/01/2023, PN 963820, "Pilot Jet 35" actually measures .53mm (ID) definitely not 0.35 mm The Rotax fuel line return restrictor jet is almost certainly a Mikuni type VM 22/120 #35 - Why ? The design/shape, dimensions & number of holes, matches the Rotax part. Further the Mikuni numbers relate to flow (not a specific jet ID). Unfortuatly I have been unable to find the flow data. Are you able to assist? Edited January 28, 2023 by skippydiesel Link to comment Share on other sites More sharing options...
facthunter Posted January 28, 2023 Share Posted January 28, 2023 It's easy to open up one that's a bit too small. Use a sewing needle with a flat ground on one side as a reamer. The flow rate is easy to check over a shorter period than one hour. I'd start with a .012" Hole Nev Link to comment Share on other sites More sharing options...
skippydiesel Posted January 28, 2023 Author Share Posted January 28, 2023 14 minutes ago, facthunter said: It's easy to open up one that's a bit too small. Use a sewing needle with a flat ground on one side as a reamer. The flow rate is easy to check over a shorter period than one hour. I'd start with a .012" Hole Nev True I could just purchase a Mikuni #10 (the lowest flow rate)? and adjust it to my own liking - prefer to get the correct or slightly undersized jet & modify. FYI Mikuni do not publish jet ID dimension's and all their jet numbers relate to flow(also unpublished) at a ? pressure (presumably a standard). As for "check over a shorter period" why when I can fly (real world test) for or over, several hours, then divide the Hobbs time by the contents of the container/tank. Link to comment Share on other sites More sharing options...
IBob Posted January 28, 2023 Share Posted January 28, 2023 This seems to be going round and round. 1. I think you can be confident that what is required is a 0.35mm jet or orifice. 2. As noted above, I measured a spare in the splitter block as supplied with my Savannah kit, and concluded that mine is over 0.35mm but not as big as 0.4mm. This works fine in my aircraft. 3. If you're really stuck, I can send you one from that block (there are two, identical, the other is used to hook up the pressure gauge.) HOWEVER: the orifice is drilled into the end of a threaded spigot, and you would have to identify the thread and have something to screw it into. That, or rework it to fit into whatever you have there. See pic below. 4. A further possibility might be to contact https://www.munichmotorcycles.com.au I recently had a very useful conversation with M61A1 here and he recommended them for carburettor jetting. Link to comment Share on other sites More sharing options...
skippydiesel Posted January 28, 2023 Author Share Posted January 28, 2023 I am hoping a Forum member has experience with (hotting) engines and has played around with carburettor jetting. This helpful person may be able to suggest which Mikuni type VM 22/120 jet(s) might give me the 3-4L/hr I seek - if flow rate too low, could then use the Nev method . Link to comment Share on other sites More sharing options...
IBob Posted January 28, 2023 Share Posted January 28, 2023 (edited) I don't think the people proposing here to stick variously modified pins or needles in the hole have looked at just how small 0.35mm is: I spent many minutes with grades of emery paper cutting a taper onto the tiniest needle I could find in order to try and measure the jets in the above pic. As a comparison: a standard fine dressmaker's pin in 0.6mm in diameter. Edited January 28, 2023 by IBob 1 Link to comment Share on other sites More sharing options...
facthunter Posted January 28, 2023 Share Posted January 28, 2023 Anything modern will be injected and electronic. Can't you check this with just a boost pump pressure and the motor stopped? There would be a full range of AMAL main jets available forever as long as old english bikes exist. They are on flow rate. Obviously that will vary with pressure differential. The "pull" on the fuel depends on the engines mass airflow and Venturi size .Too big a venturi and the jet size becomes larger and insensitive and the carburetter hard to tune, Nev Link to comment Share on other sites More sharing options...
skippydiesel Posted January 28, 2023 Author Share Posted January 28, 2023 Thanks for the very kind offer Bob - my fuel manifold/distributor is a custom job. I need a smaller/lower flow, Mikuni jet to replace the 0.53mm one I have. That your system uses (about) 0.35mm gives me a factual "goal" to aim for - just need to find out which Mikuni type VM 22/120 jet(s) might be in the ball park. Link to comment Share on other sites More sharing options...
skippydiesel Posted January 28, 2023 Author Share Posted January 28, 2023 (edited) 8 minutes ago, facthunter said: Anything modern will be injected and electronic. Can't you check this with just a boost pump pressure and the motor stopped? There would be a full range of AMAL main jets available forever as long as old english bikes exist. They are on flow rate. Obviously that will vary with pressure differential. The "pull" on the fuel depends on the engines mass airflow and Venturi size .Too big a venturi and the jet size becomes larger and insensitive and the carburetter hard to tune, Nev Fuel return line Nev - not a carburetor. I guess the relative performance of each jet could be judged using just the boost pump but being a simple sort of person, I would prefer to subject the jet to the actual environment that I expect it to perform in. As for pressure - all I can tell you is, the existing Rotax jet 35 returns 7+l/hr at the pressure developed by the standard Rotax diaphragm pump. My Dynon tells me, during pre TO checks, that it ranges from 4.5-5.5 psi depending if boosted by auxiliary pump. This pressure drops to below 2 psi during TO/Climb. Whatever jet I replace, the existing one with, will be measured under the same pressure regime. Edited January 28, 2023 by skippydiesel Link to comment Share on other sites More sharing options...
facthunter Posted January 28, 2023 Share Posted January 28, 2023 I'm only talking of flow rates. Some # are size and some are flow. I thought you wanted FLOW. The AMAL jets are flow. and a change would be relative. I worry for you with the current problem insomuch as you may not be safe flying with your current situation. I'm pretty cautious with these things like fuel which even the best engines must have. Link to comment Share on other sites More sharing options...
IBob Posted January 28, 2023 Share Posted January 28, 2023 1 hour ago, skippydiesel said: Thanks for the very kind offer Bob - my fuel manifold/distributor is a custom job. I need a smaller/lower flow, Mikuni jet to replace the 0.53mm one I have. That your system uses (about) 0.35mm gives me a factual "goal" to aim for - just need to find out which Mikuni type VM 22/120 jet(s) might be in the ball park. Right, well according to this chart (which agrees with your #35 being just over 0.5mm) what you are looking for is #15 or #20: https://www.allensperformance.co.uk/carb-kit/jet-size-chart/ 1 Link to comment Share on other sites More sharing options...
skippydiesel Posted January 28, 2023 Author Share Posted January 28, 2023 1 hour ago, IBob said: Right, well according to this chart (which agrees with your #35 being just over 0.5mm) what you are looking for is #15 or #20: https://www.allensperformance.co.uk/carb-kit/jet-size-chart/ Wow! Great work IBob. The #15 looks the goods (closest to IBob's 0.35mm) , assuming that the aperture size alone dictates the flow rate. Will place my order this evening. Link to comment Share on other sites More sharing options...
IBob Posted January 28, 2023 Share Posted January 28, 2023 13 hours ago, skippydiesel said: Wow! Great work IBob. The #15 looks the goods (closest to IBob's 0.35mm) , assuming that the aperture size alone dictates the flow rate. Will place my order this evening. Skippy, I'll be really interested to see what return flow you get, once you have had the opportunity to measure that. I have seen the figure of 2L/hr bandied about a fair bit, but have never been able to discover where that came from. And I suspect the return flow on my Sav is significantly higher than that. Link to comment Share on other sites More sharing options...
skippydiesel Posted February 16, 2023 Author Share Posted February 16, 2023 First flight after fitting new smaller return flow line restrictor jet. New jet measured at approximate 0.075mm orifice, compared with 0.52mm for Rotax supplied jet. Unscrewed old, screwed in new - exact fit. Ground run pressures 5.3 psi , 2500 rpm - basically the same with boost pump on. TO/Climb Out with boost went down to 3 psi (improved from around 1.5 psi). High speed cruse at 5000ft - 3 psi without boost. So improvement all round but not as much as I would have expected. May be those that theorised a restriction (in line boost pump?) in supply may be correct. No figures yet on new jet return line fuel flow. 2 Link to comment Share on other sites More sharing options...
IBob Posted February 16, 2023 Share Posted February 16, 2023 That sounds a lot better, Skippy. (I'm guessing you meant 0.275mm, not 0.025mm.) Look forward to hearing what your return rate is! 1 Link to comment Share on other sites More sharing options...
skippydiesel Posted February 16, 2023 Author Share Posted February 16, 2023 58 minutes ago, IBob said: That sounds a lot better, Skippy. (I'm guessing you meant 0.275mm, not 0.025mm.) Look forward to hearing what your return rate is! Nope! the best I could do was get a loose fitting (.075) oxy cleaner in to the jet (next size up wouldn't go in) so actual size bigger than quoted that's why "approximate" used. As for return rate - should have drained header tank before flying the smaller restrictor BUT didn't. I do know the hrs flown on the larger jet so will be able to make a rough estimate of smaller jet flow. Will drain header before next flight, so future measure will be all small jet. 1 Link to comment Share on other sites More sharing options...
IBob Posted February 16, 2023 Share Posted February 16, 2023 There's something here I'm not understanding Skippy: 0.075mm is about the diameter of a medium thick human hair. And if you have gone from 0.52mm to 0.075mm, the cross sectional area of the port has been reduced by a factor of 48. I thought you were going for a #15 jet, which is 0.335mm? Maybe take the micrometer/vernier callipers to the oxy cleaner? 4 1 Link to comment Share on other sites More sharing options...
facthunter Posted February 16, 2023 Share Posted February 16, 2023 I "think" in Thous. .013". You'd need a very precise chuck to hold a drill that size . I came across a set of hair fine drills the other day. I have no idea why I have them but I lost 2 just opening the Container they are in. IF you can solder the original orifice it's easy to drill that to the size you need with one of the drills if you have a chuck. Nev 1 Link to comment Share on other sites More sharing options...
IBob Posted February 16, 2023 Share Posted February 16, 2023 (edited) 40 minutes ago, facthunter said: I "think" in Thous. .013". You'd need a very precise chuck to hold a drill that size . I came across a set of hair fine drills the other day. I have no idea why I have them but I lost 2 just opening the Container they are in. IF you can solder the original orifice it's easy to drill that to the size you need with one of the drills if you have a chuck. Nev .075mm is approx 3thou. .335mm is 13thou. Edited February 16, 2023 by IBob Link to comment Share on other sites More sharing options...
Blueadventures Posted February 16, 2023 Share Posted February 16, 2023 1 hour ago, IBob said: .075mm is approx 3thou. .335mm is 13thou. An 0.3mm hole is also a gas jet size. When held between both thumbs and their next finger and hold up to the sun light you will see through it. I also have a few drill bits of that size for maintenance cleaning. The Oxy welding tip cleaner wire files are to big. 1 Link to comment Share on other sites More sharing options...
skippydiesel Posted February 16, 2023 Author Share Posted February 16, 2023 (edited) I guess I had better go back & remeasure (likely re read my micrometre/failure of operator). Part of the problem is that I don't have a cleaner "wire" that is the same size, as the orifice, either too small or to large Edited February 16, 2023 by skippydiesel Link to comment Share on other sites More sharing options...
facthunter Posted February 16, 2023 Share Posted February 16, 2023 You can look through it if you hold it up to the light. Nev Link to comment Share on other sites More sharing options...
skippydiesel Posted March 10, 2023 Author Share Posted March 10, 2023 (edited) Update: The new return restrictor valve (Mikuni 15) is returning about 3.75L/hr Edited March 10, 2023 by skippydiesel 1 Link to comment Share on other sites More sharing options...
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