Microlighters

HI all,

I have just serviced my Carbs (Every 150 hour service) and it is p!ss easy. I called Niren at Aviation Engines and he shipped me the following kit.
Jet Needles, and Needle Jets
All the various rubber rings
4 rubber grommets for where the cables come in to the carbs
the two rubber caps for to close the vacuum vent on the side of the carbs
the Choke pistons with gasket
The Sieve Sleeves

Total cost including overnight shipping R670.

I then followed this guideline to service the carbs,

http://www.gregperkins.co.za/flying/dow ... uretor.doc

Took me 30 minutes each and AUKie is running beautifully

Thank you Morph

Here is another reference for rebuilding your carb.
http://www.800-airwolf.com/pdffiles/ART ... t%2052.PDF

Morph, did you notice a difference in performance, etc etc after yopu serviced the carbs, or did you just do it as piece of mind??
i find that sometimes, when motor is hot, when she's idling, and I put my feets down on the power, it takes a moment or 2 for the motor to realise that HELLO, I NEED POWER. For this reason, I always have about 1/3 power on finals, and drop the power when I am totally committed to landing., Wonder if doing the carbs might make the performance a little better.

kb wrote:...i find that sometimes, when motor is hot, when she's idling, and I put my feets down on the power, it takes a moment or 2 for the motor to realise that HELLO, I NEED POWER...

kb, this usually indicates a TOO LEAN mixture.

If you have a cable-actuated choke (here we go again...it's an "enricher") then you can apply the choke immediately as you hit the gas. If the response from the motor is better then you have a LEAN setup. (See, that's why it's called an enricher, and not a choke :D )

If you've verified that it is a lean mixture, then change the clip position on the needle DOWN one notch. This raises the needle and makes it a bit richer. But, remember, it makes it richer throughout the range from idle to 3/4 throttle. Alternatively, you can change the needle and needle jet to BIGGER NUMBERS. Bigger number sizes make the range richer and smaller numbers make the range leaner.

If it is established that it is a lean mixture, I would also turn the air mixture screw in by about 1/4 turn, which makes the idle range just a little bit richer as well.

You could also have an air leak somewhere, in any number of grommets, rubbers and gaskets but that's another lesson. Try the above for now.... :D

Duck Rogers

kb wrote:Morph, did you notice a difference in performance, etc etc after yopu serviced the carbs, or did you just do it as piece of mind??

Sorry kb, I haven't flight tested it yet. I needed to service the carbs because the grommets where cracking and it was idling funny and running rich. I also bought the plane 2nd hand and the log book says it is over 150 hours since the last carb service.

Duck,

one thing I did notice was when I removed the needle jet there was a white gundgy substance on the threads between the jet stock and the needle jet. I only saw this on one of the carbs and only there. I have no idea of what it is or how long it has been there. Any ideas.

Also I noticed the needle jet clip was in the top position instead of the 2nd position. Since I have replaced all the jets and needles with new standard kit , I have put the clip as per the manual on the second position. The plane was running a little rich before the service but it the clip was in the top position it should have been running lean

The plane did have the wrong main jet sizes when I bought it and I replaced those then. It is possible that it also had the wrong needle jet and jet needle sizes as well.

I'll watch the EGT's now to check for high/low temps and I'll check the plugs as well after every flight to get an idea of how it is running.

Morpheus, as you know, the Bing carb is a 3-stage carb.

Stage 1) The idle jet ONLY controls the idling
Stage 2) The needle and needle jet ONLY controls from immediately after idle to approx 3/4 throttle
Stage 3) The main jet ONLY controls from about 3/4 throttle to full open

The plane was running a little rich before the service but if the clip was in the top position it should have been running lean

Quite right. Couldn't have been rich in the mid-range unless it had a real wrong or stuffed-up or incompatible needle and needle jet or worn out needle or........

Check your EGT's very carefully. Every Rotax with a Bing carb has a hotspot in the mid-range somewhere within a couple of 100 rpm's apart. Don't panic when you see that. Just try and avoid that rpm range.

As you rightly said.... check the plugs. The plugs don't lie. They live there in the hot place where the heat is :D and will tell you EXACTLY what is going on in that engine.

To get back to the jetting... do you know what serial number your motor is? There are jets for 503's up to #3785371 and different ones for #3785372 upwards.:shock:

Edited: I am not too sure about the white gundgy stuff. I remember someone at the club talking about it recently, but didn't pay too much attention to the conversation I will ask this weekend and report back :D

Duck Rogers

Hi Duckie,

Obviously you've done this before :D

I brought my Challenger (503) down from Jhb to Ct a few weeks ago ie. massive altitude drop. Do I need to re-jet and reset/adjust?

GR8-Dad your main jets need to be replaced with 158's for Sea-Level flying. The rest should not be changed. Tommy Coupe might have stock here or phone Aviation Engines. They are not expensive, I think I paid R120 for the set

http://www.gregperkins.co.za/flying/dow ... retors.doc

Duck, My serial number is 4296834 so I have the new specs. The jets etc I put in are for this version of motor.

OK, I fly mainly at 5000RPM so if it was running rich there then it must have been the needle jet and jet needle, wrong size or worn. Is it not also possible that the enricher, being worn was enrichening the mixture because the gasket was not sealing properly.

I flew this morning, at 5000rpm the EGT's are in the 540deg C region and the CHT's are 140.

I'll check the plugs out later today.

Morpheus wrote:...Is it not also possible that the enricher, being worn was enrichening the mixture because the gasket was not sealing properly....

It is possible but probably unlikely because the enricher also has a rubber type gasket that is pressed down quite hard by the spring that holds the contraption together, so it normally doesn't leak. But, nothing's impossible

Duck Rogers

GR8-DAD wrote:I brought my Challenger (503) down from Jhb to Ct a few weeks ago ie. massive altitude drop. Do I need to re-jet and reset/adjust?

Just the main jet, like Morpheus said and also just make sure you have a size 45 idle jet in, otherwise it could be rich and rough on idling if it has a bigger one. You probably have a 45 because that's the standard but check anyway, you never know what a previous owner did, if you are not the first owner.

Duck Rogers

Well, I did an hour yesterday and rushed back later to check out the plugs and they are burning quite nicely thank you

I spent the afternoon replacing all the fuel lines, I had the red translucent stuff on, no idea for how long and one of the other guys at Morning Star had a problem with his splitting and spilling fuel all over the interior of the Bushbaby. It was clamped in position with cable ties. When I took the cable ties off the pipe ends were very soft and the pipes literally fell off the carbs

I replaced it all with high pressure Fuel Injection fuel hose, not see-through, but then I never check for bubbles anyway. I chose the 6mm one so you need a firm pressure to get the hose on and off. I used proper cable clamps to hold them on. I feel much better now.

Morpheus wrote:When I took the cable ties off the pipe ends were very soft and the pipes literally fell off the carbs

By doing something about something that you felt uncomfortable with....just saved you a future brown underpants moment :D

A lesson to be learned by everyone reading this......if you feel uncomfortable with something, then do something about it! Even if it turns out to be trivial or didn't need doing, you'll feel happier and more at ease :D and most likely your intuition would have been correct in the first place.

Duck Rogers