when to de-coke?

[G-OMER]

stuffed the camera down the airbox and through the cobra neck today to check the silicon had not migrated over any of the holes around the carb inlet and tilted the carb top to the rich side, all good, just hoping the weather clears up for some test flights tomorrow. also switched to BP ultimate 98 ron fuel as supposed to clear carbon out of the cylinder according to the web site, will take a few hundered ltrs to clean mine up Lol

 

 

[Bruce Tuncks]

The white deposits from avgas running are lead bromide, according to wikipedia. The bromide is supposed to make the lead volatile and exit the exhaust. Obviously not all of it does.

 

Bruce

 

 

[G-OMER]

test flight went ok, did a 2 hr sortie, i did notice my cht was up to 350 mark on warm up and taxi, but this dropped down to about 240 after a couple of mins airborne, only other thing i noticed in flight was a small vibration on my top of dash mounted gps at about 2.4k rpm, this was not there at anyother rpm. will carry out another cylinder camera inspection on my 50 hr in 6 hrs time.

 

any one know the right torque for the prop bolts on a 2200a with a gt prop

 

 

[G-OMER]

I did a 100 hr service today on my jab, I can now confirm after about 4 hrs since fitting the cobra head my plug colours are all matching, so it worked. cylinders 2 and 4 are richer, 1 and 3 are leaner, all plugs the same colour, will post pics as a comparrison. only thing I found that I was not sure about was no 2 head after taking off the valve cover the oil residue in the cover was brownish, could be condensation build up as the jab has not been ran for 3 weeks (in the UK)the ali around the valve spring on the head showed a light brown staining, so poss blow back from the valve guide, all the other heads were fine. now to do a leakdown tomorrow

 

Regards

 

Gary

 

 

[jetjr]

I did a 100 hr service today on my jab, I can now confirm after about 4 hrs since fitting the cobra head my plug colours are all matching, so it worked. cylinders 2 and 4 are richer, 1 and 3 are leaner, all plugs the same colour, will post pics as a comparrison. only thing I found that I was not sure about was no 2 head after taking off the valve cover the oil residue in the cover was brownish, could be condensation build up as the jab has not been ran for 3 weeks (in the UK)the ali around the valve spring on the head showed a light brown staining

Im of the belief this staining is most likely valve guide leakage and IS very important. This head should be stripped and guides checked deposits from burnt oil etc can grab valve and lead to serious problem

 

This inspection for these stains is right up there with egt and leak downs in my book on Jabiru engines

 

 

[old man emu]

G-OMER,

 

How the hell did you do 100 hours in December? All I've seen since I've been in Lincolnshire is rain, overcast and wind. Are flying around IFR?

 

OME

 

 

[G-OMER]

? 4 hrs

 

 

[old man emu]

Mis-read Post No 29. I understand that you did some work on your engine a few hours before the 100 hourly, then did the 100 hourly and saw the results of your work. Right?

 

Now I know why you've done 4 hours in December.

 

OME

 

 

[G-OMER]

yep, correct

 

 

[G-OMER]

leak downs were

 

1 80/65

 

2 80/72

 

3 80/75

 

4 80/72

 

could only get 20 min flight after the service the next day from a 3 week lay up

 

 

[old man emu]

I don't like No 1 cylinder.

 

OME

 

 

[G-OMER]

me neither, is there a trend forming?

 

 

[old man emu]

Don't know about a trend. My fist guess would be operator error. Try doing the leak down tests starting at No 4 and working back to No 1. If you get similar results for No 1 as you already have, something might be happening. You should hope that the problem is a bit of soot lodged at the valve seat.

 

Always go for the simplest cause first. Don't get ulcers worrying about a major problem yet.

 

Have you put skis on your plane yet? I was down in Cornwall in the sun for the weekend. Didn't hit the snow until we got back in the Cotswolds!

 

OME

 

 

[G-OMER]

no 1 has been

 

 

[old man emu]

G-OMER,

 

Don't go in strike!

 

OME

 

 

[G-OMER]

no 1 has been like that for the last 3 leak downs regardless of what pot you piss in first

 

 

[old man emu]

Step 2. Pull the head off No 1 and check that the valves are properly lapped into the seats.

 

OME

 

 

[G-OMER]

thats the next move, had a top end overall course in december with Roger Lewis

 

 

[old man emu]

don't forget when you go to put the cylinder back on to make sure that the gaps in the piston rings are not lined up. Off set each ring gap from the others.

 

OME

 

 

[G-OMER]

yes. yahoo jabiru forum, another bloke with a 80/65 on number 1. thats 5 popped up in the same amount of weeks. trending....

 

Gary

 

 

[G-OMER]

Ok, I assisted my friend with his low leak down on pot 1, his turned out to be rings lined up, so re align and new valves seen the pressure come to 75/80

 

A couple of weeks later I did mine, rings not in line but second ring stuck in piston and heavy scoring 90 deg from the stuck ring.

 

Replacement barrel fitted, new rings and replacement head, test run and 80/80 pressure seen.

 

Test flight today seen pot 1 temps climb out 350, cruise 288 at 90 knots 2600 rpm. Pot 4 showed 300 climb out and 240 at 2600 90 knots

 

I varied the temps by backing off etc

 

 

[Keenaviator]

fuel is 8 to 10 ltrs per hr. #2 #4 are lean as plugs white, the other two are black rich, its not jetting its the distribution through the plenum box I think, more is going to 1 side than the other. i have searched the net and I think a cobra head with the cross in it or a plate baffle should improve the distribution to these pots going by others and various things I have read, this is my next move. any one had experience using these?

 

[eightyknots]

You pour De-Coke into each cyclinder and leave overnight, you will then have nice shiny cyclinders. .ONLY JOKING...ONLY JOKING...ONLY JOKING.

Perhaps Coke (Coca Cola) would work better?

 

 

[Thirsty]

You can tilt the carb slightly to one side or the other to even out your mixtures left to right. Can't remember which way riches but a search here should find the relevant info.