Guest Qwerty Posted June 23, 2009 Posted June 23, 2009 My jab starts instantly but won't run. If I move either throtle or choke it dies. It just stops. It usually stops 3 or 4 times anyway. After it has been running for about 90 - 120 seconds with full choke and no throtle and if I can push the choke off quickly enough it will run perfectly. It runs fine when warm. An additional earth has been installed fron the standard eng mount earth to the cap of the starter motor. The float level has been checked. Hot idle is 850 - 900 rmp. The aircleaner is OK. There is a FRP connector from the scts hose into the carby. The carby vent hose is properly installed. New plugs gapped to 0.020" have been installed. New 15W50 oil (and filter). Both mag. gaps set at 0.010". Rotor caps and buttons are OK. The choke circuit has been checked OK. So wots wrong with it? Any ideas?
Tomo Posted June 23, 2009 Posted June 23, 2009 Start it with choke held out tight, leave it like that for a bit (10seconds or more, depending on how cold it is), rev it to about 1500rpm with choke still out, then push the choke in slowly with engine still at 1500revs. Then slowly bring the revs back... That's what I had to do this morning, if you push the choke in without first bringing the revs up, it just stops on you... I'm not sure if you're already doing that, but that's what I've found to be best when the engine is cold, mind you though, I've only ever started a Jab a few times now... so I'm still pretty green in this area.!:big_grin:
Guest ozzie Posted June 23, 2009 Posted June 23, 2009 What is the oil pressure showing just as it starts to run. maybe it is having a hard time pumping the cold oil until it can pick up a few revs.
Guest Qwerty Posted June 23, 2009 Posted June 23, 2009 Tomo, If I even think of moving the throtle....it dies. Ozzie, oil press is high but in the green.
Guest Ken deVos Posted June 23, 2009 Posted June 23, 2009 Is it a 4, or 6-cylinder motor? Also, what is the ambient air temperature when this problem occurs?
Guest Qwerty Posted June 23, 2009 Posted June 23, 2009 Its a 6. Any ambient temp at first start. So far, it will do it with ambient up to about 12 or 14 C.
Yenn Posted June 23, 2009 Posted June 23, 2009 Ime not used to that cold but you should be able to increase revs with the throttle, even with full choke. Will it run with full choke without being obviously too rich? Run it with choke for a minute or so and then try to increase revs with the throttle. if it stalls then I would think there is a problem in the carbie somewhere. Maybe you should talk to jabiru, they may have the answer at hand.
Tomo Posted June 23, 2009 Posted June 23, 2009 Tomo, If I even think of moving the throtle....it dies. Mmmm, strange to say the least! Is that with the fuel pump on or off? And it dies when the throttle is moved even with the choke still out?!
Guest brentc Posted June 23, 2009 Posted June 23, 2009 On the face of it, I'm thinking that it can only be fuel / carby / choke related and not electrical. Has it always had this behaviour, or even a little sign of it? I'm thinking that it could be something gummed up in the carby like the idle jet. If it were my aircraft I would try the following: - Drop off the bowl and whilst carefully supporting the floats blow compressed air carefully up into the carby from the bottom up - Undo the main jet and blow it out and make sure it's clean etc (blow with compressed air too) - Ensure that your choke is going on fully and is working completely independently of the throttle - If that doesn't work I'd consider removing and dismantling the carby for closer inspection hoping to find some kind of blockage, such as the breather to the outside environment. Thinking back I have experienced similar symptoms when I was running the lean-burn kit but this went away when I changed to richer and also ensured that my choke was pulling on fully. If I was to start mine now with choke on and add throttle in the first few seconds I would probably get the same results as you have described as the choke and throttle aren't really meant to be used at the same time. I guess you're also thinking that it could be electrical but I'm struggling to see what could be faulty and causing this. I await your results no matter what the problem is. Of course you realise that this is payback to you because you destroyed a perfectly good Jabiru by putting a tail wheel on it.
Guest Qwerty Posted June 23, 2009 Posted June 23, 2009 I'm told that its not running too rich with full choke. As I said if I even think of applying throttle or easing off choke in less that about 2 min...it dies. I've already spoken to Don, he gave me the list of stuff to do in the original post. Fuel pump on or off makes no difference. Ive only just bought the a/c so I'm not sure of the history, good point though, I'll call the previous owner. All the blowing and cleaning of the carby has been done. I don't think that it is electrical, the bugger starts very well...it just wont run. Sorry Brentc but its only those who can't fly tail wheels that bag them. They are so much better that tricycles in so many ways, not the least of which is not carting around all that drag haning off the front of the a/c like some hideous wart. Is there any way that a slight leak in the diaphram in tha carby will give the problem described. BTW I'm not a mechanic, I'm just guessing.
Guest drizzt1978 Posted June 23, 2009 Posted June 23, 2009 This might be very unrelated BUT... I built a 280zx engine and shaved the head to get more compression and did some work on the inlet. ...Do you think it would start in winter?? Was a u know what to start in cold weather..... I also had a Sr20det that i built...tough son of a..... Any way it started running real bad when it was cold...that was a blown head gasket....so you could look at compression leaks if you want... This causes water on the cylinders due to condensation, also , have you changed the fuel filter, and worst case the fuel.....??
facthunter Posted June 23, 2009 Posted June 23, 2009 clearance. Check compression (cold) and valve clearance. IF the inlets are being held off the seats it will run like a dog till the motor heats up. (long shot but worth checking). Nev.
Guest Qwerty Posted June 23, 2009 Posted June 23, 2009 Negative hydraulic lifters. Valve clearances 0.010" cold.
bushpilot Posted June 23, 2009 Posted June 23, 2009 Silly suggestion I'm sure, but here goes: Could it relate to the nose-high attitude? Pulling fuel up the hill, or carby floats sticking, or whatever...
Captain Posted June 23, 2009 Posted June 23, 2009 Based on your description, it has to be something in the fuel circuit and I'd guess at a sometimes blocked idle circuit or idle jet in the carby ... maybe a loose obstruction in there somewhere. Have you checked those specific passage-ways? Maybe look for something tiny, as it won't take much if a bit of loose flaky stuff gets in there.
nong Posted June 23, 2009 Posted June 23, 2009 Hullo qwerty. I have put up with a fair bit of similar trouble on both 4 and 6 cyl. Jabs. One observation is that the choke system, even when functioning correctly, in many cases struggles to enrichen the mixture sufficiently. Sorry, I have no cure. This might be a worthwhile development project for Jab, to keep us 'southerners' happy. Make sure you are using at least the number 45 pilot jet. There might be a case for going bigger than that in southern Australia but I haven't yet explored that option. You could do worse than to pull out all the jets plus the needle, and with them in front of you, call Jab and say "HELP!", "this combo doesn't work". My hydraulic 2200 functioned perfectly until Jab sent a needle that was a mandatory fit ( flying school use ). That was where the trouble started. The fix was to replace the pilot, needle and even the main jet with versions having a greater flow rate. If problems persist, it's time to bring out the big guns! I'm talking about PRE-HEAT. Jam a 2000 watt hair dryer ( Remington Salon ! ) up the guts and stuff a coupla rags in the cooling air inlets. Ten minutes of that and the whole induction system and even the cylinders will be toasty warm.
Guest drizzt1978 Posted June 23, 2009 Posted June 23, 2009 Hey qwerty in the the thread about why people hate jabs, they are talking about opening the carby heat to start a cold engine....give it a read and a go?? trying to help out over here!! good luck
Guest brentc Posted June 23, 2009 Posted June 23, 2009 I was told by one of our pilots who is at Lake Eyre / Marree at the moment that most of the Jabs that are visiting there at the moment won't start in the mornings. There's been a string of private 170's and 230's visting there apparently.
Gibbo Posted June 24, 2009 Posted June 24, 2009 I've had the same problem with several Jabs on very cold mornings in Central Aus. Trick I found was to 'just' crack the choke slightly as you turn the motor over on the starter motor. Don't touch the trottle for at least a minute and everything should be ok. Part of the problem, I'm told is the alloy block will actually shrink in the cold weather thus the heating option works. Gibbo
Modest Pilot Posted June 26, 2009 Posted June 26, 2009 The coke is actually not a choke at all it's a start circuit. Only works if the throttle is completely closed. On my J230D I close the choke quickly while cracking the throttle open at the same time on cold starts. Check the carbies float cutoff level is correct and make sure that no fuel sloshing compound has got passed the fuel filter. ( it did on mine and the fuel filter was dead clean when I cut it open and inspected it) It's white on the new Jabs and the very devil to remove, you will need to grit blast the fuel bowl to remove it. This stuff doesn't seem to get in the jets but can build up enough to block the entry to the start curcuit.
Guest Cloudsuck Posted June 27, 2009 Posted June 27, 2009 G'day qwerty, I didn't realise it was you and that you were talking about my old plane. Mate, Leave the choke all the way out for a couple of minutes, then BRISKLY push it in and as you do, catch it with a bit of throtle over the dead spot. If you try to ease the choke in it will snuff. I gave a demo of this to the other guy and I thought he would have passed it on to you. I guess he just took his money and headed for the hills. This technique works 100% of the time. Easing it in = Snuff.
bushpilot Posted June 27, 2009 Posted June 27, 2009 So C/S, I might try the technique on mine - but when do you apply the throttle - as you are 'briskly' pushing in the choke?
Guest Cloudsuck Posted June 27, 2009 Posted June 27, 2009 So C/S, I might try the technique on mine - but when do you apply the throttle - as you are 'briskly' pushing in the choke? Yep, thats right, as you push it in. I guess they are all individuals and depends on your setup but as someone said above, the choke and the throttle are not designed to be operated at the same time. Even after the engine has been running for a minute or so, It is still cold and needs to be enriched so if you close the choke, you need to open the throttle and get the intermediate circuits in the carb working and not just the idle circuit.
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