Microlighters

Hi all you clever peolple.

I fly a Kolb Mark 3 classic that is fitted with a Rotax 618.

The engine is fitted with the intake manifold and has size 135 jets in both carburators. EGT and CHT runs normal.

Now. I get a consumption of 25l/hour!!!!!!!! IS THIS NORMAL????????

I tried to fly at diffirent throttle settings, but it does not make any diffirence.

Please help? This makes flying too expensive!

Regards
Don Barrie
(Standerton)

flywild wrote:Hi all you clever peolple.

I fly a Kolb Mark 3 classic that is fitted with a Rotax 618.

The engine is fitted with the intake manifold and has size 135 jets in both carburators. EGT and CHT runs normal.

Now. I get a consumption of 25l/hour!!!!!!!! IS THIS NORMAL????????

I tried to fly at diffirent throttle settings, but it does not make any diffirence.

Please help? This makes flying too expensive!

Regards
Don Barrie
(Standerton)

Hi Don,

Sounds a bit high, I have a Rans S12 also fitted with a 618 with intake muffler and my fuel consumptions is quite a bit lower.

A lot depends on the RPM, my prop, a 3 blade NC on a 3.47 gearbox, is set quite coarse, on the ground my max RPM is about 5900 and in the air max 6300. Depending on load, and haste, I cruise at between 5200 rpm and 5900 rpm burning from 13 to 18 lph.

I cannot remember the jets I have in but they are the recommended ones for sea level (I am in GP) so the engine runs a bit rich but that is ok with me as I do not want to change jets when I fly down to the coast. My EGT's are quite low at around 580 max. I do know you are suppose to run 2 different size jets on this engine and the intake muffler causes a change in jets as well.

What RPM do you fly at?

Fly safe,
Rudi

The jets you are supposed to run is a 165 and 170.

Stephan van Tonder wrote:The jets you are supposed to run is a 165 and 170.

With or without the intake silencer?

that is without..

Stephan van Tonder wrote:that is without..

Ok, thanks, I think mine with the silencer uses smaller jets, around 135/138 if I remember correctly. I believe the intake silencer does rob you of some power....

I doubt that they would be that much different. This is probably the sizes our friends at Aviation engines recommend for the 'reef' and why people lose engines due to lean running. The 618 in particular really doesn't seem to like running lean. The difference between 130 and 165 is massive in the terms of jets and if you have jets that small you are probably busy killing that motor. I suggest you have a look at what really is in there.

Stephan van Tonder wrote:I doubt that they would be that much different. This is probably the sizes our friends at Aviation engines recommend for the 'reef' and why people lose engines due to lean running. The 618 in particular really doesn't seem to like running lean. The difference between 130 and 165 is massive in the terms of jets and if you have jets that small you are probably busy killing that motor. I suggest you have a look at what really is in there.

Yes, will have a look, planning on servicing the engine this weekend. I looked up the sizes, for sea level, in the manual when I originally bought the plane. My 618 is running quite rich according to the EGT's, up here on Reef anyway, at the coast it seems about right. The motor now has around 500 hours with this setup.

Ok, just had a look in the 618 manual, for sea level without an intake silencer the main jets should be 160/170 and with intake silencer 135/145. The 135 on the PTO side and the 145 on the MAG side.

Shees I would drop that intake silencer

Stephan van Tonder wrote:Shees I would drop that intake silencer

Yes, I was thinking the same......

Rudix wrote:Ok, just had a look in the 618 manual, for sea level without an intake silencer the main jets should be 160/170 and with intake silencer 135/145. The 135 on the PTO side and the 145 on the MAG side.

618 klink baie soos my pêlle. Raak raserig as hulle aan die suip gaan.

Very curious about the difference in consumption with and without the silencer. As Stephan says:

Stephan van Tonder wrote:The difference between 130 and 165 is massive in the terms of jets

The silencer must really throttle the inlet air - (read power.)

I confirmed the jetting. They are 135 and 145. The highest EGT is 590 when thottled back to about 75% power. Cruise at 6250rpm.

The plane still maintains at 6000rpm, but I found no diffirence in the feul consuption.

Any mare suggestions?????

Regards
Don

flywild wrote:I confirmed the jetting. They are 135 and 145. The highest EGT is 590 when thottled back to about 75% power. Cruise at 6250rpm.

The plane still maintains at 6000rpm, but I found no diffirence in the feul consuption.

Any mare suggestions?????

Regards
Don

Your jets and EGT's are the same as mine but your revs are very high!

The only time I see 6000 is on take-off, then 5700-5800 during climb and cruise 5200-5600 depending on haste. My plane (Rans S12) will maintain alt down to about 5000 rpm, even lower if I trim the nose way up. If I cruise at 6250 rpm my plane flies at close to VNE

I think you need a bit more pitch on your prop.

Your engine will also survive much longer if you can get the rpm a bit down. As rudi says - pitch it more a bit and see if things improve.