Going lean towards end of flight....

[jimmyhorns]

Hi all... slightly odd situation now, or maybe not that odd time will tell.

My Irvine 39ABC is now well and truely run in on my hawk 30, its had about 4 gallons through it now...

So today I thought it was about time I leaned it out a bit, so I set to that task today, especially now that I have a temp sensor on the head.

The advice about feeling the backplate doesnt work on this engine, its always hot at the end of a flight, even when the engine is run sloppy rich..

Anyways, the biggest problem I have is that as the fuel level goes down (or the engine is running for longer) the mixture gets progressively more lean.

There are only about 4 clicks between crappy performance and probably too lean (noticeably less smoke), and the flying temps range from 80 degrees C for sloppy rich to 146 degrees C for too lean.. from what I understand this engine likes to 'run hot' but I could be wrong..

The fuelling is ::

Standard tank/standard clunk --> align 3way fuel filler/filter for 600 --> carb (no header tank)


Im using Optifuel 20%nitro at present


So... once again... answers on a postcard please, thanks in advance.

James

[Gate88]

The clunk line is probably holed or split so as the fuel level drops below that level it starts to draw less fuel.

[jimmyhorns]

Its only seen about 30 flights on that clunk/tube, but will take a look at it for sure.

[Gate88]

Its only seen about 30 flights on that clunk/tube, but will take a look at it for sure.

Its not always the number of flights, it could have been a dodgy bit of tubing, it could be down to not venting the tank before storing, there's a whole bunch of things that affect it, but nearly every time Ive heard of similar symptoms its been the clunk line at fault.

Its a two minute job to replace so even if you cant see a hole you might as well replace it and see if that cures it.

[jimmyhorns]

Yes ive been doing a bit of reading up....

what do you think about fuel magnets?...

[Gate88]

Yes ive been doing a bit of reading up....

what do you think about fuel magnets?...

Theyre ok I, dont use one myself, you're probably better off just fitting a header tank, it all depends on how hard you throw it about really.

[jimmyhorns]

Not super hard.... well not intentionally

Looks like a header tank it is then......

So venting the tank is absolutely necessary then?.. Ive never had issues on my fixed wing, but ive read lots of people suggesting either leaving the tank full at the end of a days flying, or at least filling it and emptying it to make sure clean air is in the tank?...

[Gate88]

Venting is not essential, some people say it can prolong the life of your fuel lines but it's better just to replace them every now and again then you know you're not going to have problems in flight.
And yes you vent by filling and emptying at the end of a session or by just leaving the tank full of fuel, that works ok so long as it doesn't leak on the front room carpet!

[jimmyhorns]

Ah, perhaps I could interest you in my novel 'no drip' solution then?....:

http://www.rcheliaddict.co.uk/main-d...tml#post874531

[Gate88]

Great! Except for when it's pi$$ing out of your pressure line or tank grommets!