I have a problem with my new Irvine 72 which has been run-in properly. The problem is that when I start the engine it sinks initially as the throttle is moved from low to high but after warm up runs good at full throttle. But the throttle response is not good. From Idle to full throttle the engine sinks and tries to quit as someone squeeze the throat and it becomes difficult to inhail...

If its the needle low/high please guid me how can I adjust it. Other than this problem the engine runs very good very powerful. I am using 12X6 apc prop. Starting is also very good. Also I had a crash landing because of this problem as the engine quits during a loop (vertical).

Is the engine spank brand new? If not, was it broken in at all and how? Basically the procedure is to set the high speed needle first. Use a tach if you have to and set it for peak, then back it off a couple of hundred rpm for now. Once that is done, set the low end so that when the throttle is advanced in a normal manner the engine transitions cleanly. There are several other factors to consider such as tank location and height above the needle centerline. Let's get some basic info first_bob

Hello!
If ithe engine "sinks" , hessitates ...then it´s to lean.....open up the low speed needle 1/4 of a turn or more a see the results....

Regards!
Jan K
Sweden

Te engine is new and broken-in per the manufacturer instructions. Okay the high speed needle is easy to adjust but it is difficult to adjust the low speed needle. If is difficult to judge whethetr the low speed end is rich or lean... The transition is not smooth and the engine tries to quit when advanced from idle to full... The tank position is fine.

It sounds like your low speed needle is too rich. Screw it in a 1/16th of a turn at a time until your transition is what you expect. Many engines come with factory low speed settings that are too rich. After you get it where you want it then reset the high end again as the 2 needles are inter-related to each other.

My procedure for trying to find the correct needle setting from scratch is this. I screw the needle all the way in. I then know that it is totaly wrong, I am not playing around trying to guess rich or lean.
I then screw it out a quarter turn at a time until I get close. Fine adjust to suit.

Ed S

Is the low speed needle rich or lean...

There are two posts with opposite suggestion... but please I need some clear and definite answer whether the low speed needle is rich or lean based on my previous explanation.

Start the engine and run it at idle. Pinch the fuel line between your fingers to stop any fuel from going to the carb. If the engine immediately loses revs then it's too lean on the idle mixture screw. Wind the screw out 1/8 turn and try the pinch test again. What you're aiming for is that when you pinch the line the engine should continue running for a short time while very slightly increasing it's revs before starting to die off. A very slight increase in revs means it's just barely on the rich side at idle.

If the idle mix is too rich then the revs will rise fairly considerably for several seconds when the fuel line is pinched. In that case turn the idle mixture screw in 1/8 turn and repeat the test until you only have a slight rise in revs.

The 12x6 is kinda small for the .72, if it is like my older Q72 it will turn a 14x6 about like a .91 would.