Bill Posted June 29 Posted June 29 Our privately operated J160C (2200) has approx 610hrs over 17 years. Over the last 20hrs the engine has been running rich, as when removed the NGK spark plugs are a dense sooty black (prior to that they'd always been light tan). The only work / mods to the carby have been; in 2008 per JSB 018-1, Idle jet #35, Main jet #245 & Needle #290. In 2022 the diaphragm was replaced. Until about 20 hrs ago we used Avgas but since have changed to Shell Premium 98. The fuel level in the bowl is, as per the book, 13mm below the top of the bowl. Advice / suggestions please. Thanks, Bill
Blueadventures Posted June 29 Posted June 29 I'd start with a carby clean / service and new o rings and adjustments as per Jab manuals. Then see how it performs.
pluessy Posted June 29 Posted June 29 Check your metering needle and seat for wear, they need replacing after a while. Worn needle & seat are causing richer mixture in the part-load range. On aircraft, you will find a worn spot where the piston/needle sit at cruise power. The needle should be a smooth "taper" all the way and the seat a round hole (worn seats are oval).
Kenlsa Posted June 30 Posted June 30 You will find that if you went back to avgas the plug colour would be ok again. Nothing is broken. i have done exactly the same as you when the SB came out. Mine was on a Gen 1 engine. I changed to mogas and found that it was too rich with the 245 main jet ( up from the 220 main) at the 2800 cruise rpm as it seemed “hard” sounding. so I split the difference and went with 235, perfect . I too went wth 13 mm pool depth as I physically checked a number of jabs and found that it was never close to the 10mm touted, with everyone running 12-13 mm. it still runs great on mogas but the plugs are still black. This has not been a problem with potential fouling and I change the plugs at 50 hours. Just for giggles I used a tank of avgas and found the plugs were ok deposit wise. Mogas is slightly denser than avgas and motorcycle racers used to drop one jet size to compensate. I too found this on my high hp z1000 Kwaka . Ken 1
Kenlsa Posted June 30 Posted June 30 FYI we have had Gen 2,3,4 engines in our fleet and with the Gen 4 there was very little deposit wise when we switched to mogas. Our fleet of 5 jabs have run mogas exclusively for the las 3 years and it has been great, with no lead fouling on the valves every 300 hours
kgwilson Posted June 30 Posted June 30 My Gen 3 has run Mogas since new. The plugs are always black after taxying back to the hangar. The insulator inside the plug is a lighter brownish colour. If you shut down after applying plenty of power they are probably a much lighter colour but that is virtually impossible to do so by the time you shut down they will be black. It isn't a problem, it is normal. The time to look at issues is when fuel consumption increases for no apparent reason.. The consumption of my Gen 3 3300A engine varies from 18 lph at about 95-100 knots low level at 2750-2800 rpm to 24 lph at 120 knots (130 knots TAS) at 8000 feet 2850-2900 rpm.
440032 Posted June 30 Posted June 30 Perhaps describe in detail how you have determined its running rich - and at idle, at cruise, full power, all of those? What are the symptoms you see? Just the plug color but no actual running problems?? I run avgas pretty much all the time, but when I did run 95ULP for about 2 years, the exhaust went sooty black real quick, can't say about the plugs, never needed to look. 2-3 years ago I had rich flooding at idle and it was nothing to do with the carb. Checked all that, spoke to a trusted carb expert. Carb float level perfect, and carb was not flooding "on the bench"- only in the plane when it was at idle. Faltering idle that would come and go. Reading through all of the jabiru manuals there were clues. Overhaul manual - "carb flooding - electric fuel pump giving too much pressure". I don't use the electric pump at all, so it could not be that. The mechanical pump though????? Overhaul manual describes fuel pump pushrod has a 0.10mm length tolerance. Why would the length change? It can't. "Effective length" can though: I determined this was the problem with the mech pump by bypassing it, just ran it on gravity feed. No rich, no flooding. Mech pump setup is (for mine at least) PUMP - GASKET - NYLON SPACER - GASKET - ENGINE. My gaskets had crushed down from about 0.70mm thickness each, to 0.36mm T each. I had lost 0.72mm of thickness total. Remember the 0.10 pushrod tolerance? It's set at that to give the correct fuel pressure I presume. I was way past that. It's just a stock quality automotive pump, nothing special. My fuel pump was effectively 0.72mmm CLOSER to the engine that it should have been, the pump was over pumping - too much pressure (for idle at least) (The pump lever has way more available travel than the pushrod can supply.) Made new gaskets from 0.70mm quality gasket card - PROBLEM SOLVED INSTANTLY - nothing to do with the carb. Why did the gaskets crush? Too much bolt checking? Shit gasket card? Both?
Bill Posted June 30 Author Posted June 30 Thanks 0032 (& everyone else who responded). Firstly we've determined it's running rich because of the sooty plugs (& also a sooty exhaust). The fuel consumption hasn't changed - historically 14.7 lph. The engine is operating normally - no problems at idle, cruise or WOT. Most of our flying is cross country of >1 hrs at 2850 - 2900 rpm, giving a TAS of 103Kts. Re your mechanical fuel pump - you determined it was flooding at idle because revs were not constant / surging?
440032 Posted June 30 Posted June 30 Engine was faltering at idle, trying to cut out. All this was there one day, and not the next. Took a while to solve. I had a mate look and he could see some black smoke when it was doing it. Same faltering at idle on base and final but a little throttle kept it going, I never had any fear it would stop, it was just annoying and I knew it was not right and had been perfect for the first 500 hrs and 17 years. In all that time I have never fiddled with the carby. If it aint broke, don't fix it. Mine is about same 15LPH fuel average. My plugs are always good color on avgas - I never looked when using mogas. Exhaust is grey with avgas, sooty black on mogas. Runs exactly the same.
Red Posted July 1 Posted July 1 Just a reminder to confirm the compatability of your fuel system when using Mogas containing Ethanol, I believe some Jabirus have Fibreglass tanks
Bill Posted July 1 Author Posted July 1 Premium unleaded Mogas (Shell Vortex 98 in our case) does not contain ethanol. 1
440032 Posted July 1 Posted July 1 A mate recently had 98 fuel dissolve his aviation grade thread sealant on his Sonex fuel fittings - fittings that survived for years using avgas and 95. the moment he used 98, all over red rover. God awful sticky shitty mess. (I don't have a Jabiru (plane) nor a glass tank, but great advice from RED.)
Red Posted July 1 Posted July 1 3 hours ago, Bill said: Premium unleaded Mogas (Shell Vortex 98 in our case) does not contain ethanol. That's good, over here the last availabe Ethanol free fuel (Esso Super unleaded) started adding ethanol last september, hopefully you guys get to have the good stuff for a while yet.
kgwilson Posted July 1 Posted July 1 Ethanol doesn't affect glass reinforced vinylester fuel tanks which is the only resin to use. This can not be said of glass reinforced polyester tanks. These are not recommended for any fuel type. 1
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