Irvine 39 abc setup help

[snukiedog]

Hi , I have recently installed an irvine 39 abc in my heli , fingers crossed I have completed the running in correcly(1.5 lts of fuel(15%nitro 18%synth oil))I followed the manual for throtle and times. My problem now is the fine tuning, at the moment I have the main 2 turns from closed, when I start to lean in alittle more I can notice the change in sound at high throtle but when I drop the gas nothing happens for half a second and the revs increase with a distinct lack of smoke(up until this point there is plenty of smoke) and after a second or 2 the revs begin to come down, would I be correct in thinking that this is a sign of too lean? forgot to say that the engine is in the heli strapped to a bench with no rotor head or tail rotor assembly; if anybody could pass me any tips or infomation they would be much appreciated!!!
many thanks Snukiedog

[hawkman]

Hi there,

There are two settings, usually, for the carb....the main needle is the larger one...which it sounds like you already know. The other setting is the 'low end' or the idle needle...this is sometimes located within the throttle barrel...look for a small screw...but dont adjust it yet.

Ok...run the engine and get it to a nice idle..now pinch the fuel line about 3 to 4 cms back from the carb...and listen to the engine idle...if the revs increase straight away you are too lean....if the engine idles for 2 to 3 seconds before rising in revs and then stopping then you are ok. If it goes for 3 to 4 seconds and longer its too rich.

Too rich? screw the idle or low end needle IN...use very small adjustments...a quarter turn will make a difference.

Too lean? then screw the low end OUT a touch.

Repeat the pinch test and adjust as needed.

The low end or idle will affect the engine revs from idle to about mid range...the main needle will have an affect of course but 2 turns out from closed sounds about right for this.

Too lean an engine usually means the engine can be very revvy but will get hot.

Fly about for a while and then land...be careful of the rotors of course..but go to idle and use a finger to touch the backplate of the engine...if its warm thats ok...but if its hot then you could be too lean or the pitch range/throttle range needs revising...too much pitch and low revs can overload an engine...the mixture going through the crankcase helps to cool the engine and its bearings.

The engine sounds powerful enough, I have one in my loft with an old Concept which will never fly again. Just got myself an OS 37 for my Sceadu.

Rob

[snukiedog]

Hi , thanks for the response, put the head and the tail back on today fired it up and tried the pinch test at about 1/4 throtle , it ran normal for about 3 secs and then started to pick up revs, I think it's still running rich ,as when it is in idle and I give a sharp jab on the throtle it sort of gurgles and then dies also there are copious amounts of smoke ( how can I tell if it is 4 stroking as I know this is not good for an ABC engine, I don't think it is ,as I now have the needle at 1 3/4 open, but I would just like to know what the signs are)? Any way thanks again for the replies, will do some more tests and let you know. forgot to say after about 1/2 a tank I could touch the back plate and keep my finger there ,(warm but not hot).
Snukiedog.

[hawkman]

Adjust the low end then, just screw it in a touch and see how it goes. The low end screw is quite exposed isnt it?....some carbs have them recessed inside the throttle barrel.

4 stroking is when the engine idles and sort of misses a beat every couple of seconds.

It sounds like you need to screw the low end in just a touch...otherwise you are there.

If you hover and punch the collective up if the engine bogs down then the main needle might be too rich....but dont get too involved. Its ok to run a bit rich...too lean will cause damage .

You must be about right with being able to touch the backplate, its a good indicator of whats going on.

If you notice a difference in performance after a half tank thats ok...and during the day the humidity might change and affect performance too...in either case you might need to land and adjust the MAIN needle...a click or two open or closed...not sure which as I havent run a nitro for a while...though will be doing so soon

Always use a filter on the fuel line, its not a bad idea to use a filter on the pressure line from the muffler to the tank...it keeps some of the rubbish out.

Dont get carried away with fuel tank acessories etc, keep the system simple...less to go wrong then.

Use good fuel tubing inside the tank for the clunk...and check it from time to time...make sure the clunk has a good gap between it and the tank end...too close can cause problems when you least want them.

Rob