Doctor Whizz

Hi Guys

I have a new ASP S91A two stroke with idle issues I can't resolve. When I say new it is run in having had well over 1/2 gallon through it via a couple of tanks pre-flight and 5 flights, plus all the fiddling around I've been doing [&o] Might still be a bit tight but my experience with other ASP engines is that they need very little running in.

The problem is that it will sit on the ground at a fairly fast idle with no sign of problems and then just suddenly stop. No warning - no coughs or hiccups - just stop dead. The idle in general seems very good and I can slow it down to a decent setting. The pick up from idle is fine (when slow jet at optimum - see below). If I can get it flying the engine will run a tank out while doing all the flips & spins you like.

Here's the configuration and what I've tried.

Mounted inverted; 15 x 6 APC prop, tank on centre line of engine, standard pressure off the muffler, 10% nitro 18% synthic oil fuel. I think I have suffcient cooling.

I've adjusted the slow jet either way until it stops idling at all at either extreme.
I've tried different plugs including and OS 4-stroke plug in case it is cooling suddenly.
I've tried leaving the glow on for same reason - dosen't help.

Any suggestion greatly aprecaited.

w8ye

My Feedback: (16)

It is picking up a air bubble

Doctor Whizz

Good question - answer is I don't know. I will have to take the cowl off and check. Thanks for tip.

I could be something has come adrift with the plumbing as the problem started suddenly after the last flight. One day I will learn to check the simple things 1st [&:]

One thing I forgot to mention is I have fitted a rear needle valve.Thought I'd try and keep my fat fingers away from the spinning knife blade at the front.

Sport_Pilot

I would think it is either an air or vapor bubble.  Is this with remote needle?  Remote needles are bad for creating vapor bubbles as the fuel pressure drops past the needle.

Doctor Whizz

I wondered if it might be having an effect. I don't have any experience with remote needles but it did occur to me that it introduces a 'dead' volume between the needle and spray bar that may be most noticable at low flow during idle.

When it stops raining I'll get out and have a play

Thanks for the input.

RCPAUL

My Feedback: (1)

I don't know if this helps but I had a ST61 that would suddenly quit at low rpm. I finally put an OS F plug in and all is now well. I use the F plug on all my ST engines now.

Doctor Whizz

If the OS F plug is the 4 stroke plug I've already tried that one thanks

jaka

Hi!
Have you mounted the tank according to the tank mounting rule?
How large is the tank?
Have you set the high speed needle fairly rich? 200-300rpm below max rpm?
Have you set the low speed needle by ear? No pinch metod please!
15x6 is fairly large prop, but it would work. You should obtain an rpm around 2000rpm using that prop. Have you tried a 15x4W APC? Not that it would have anything with how the engine behaves though.
How is the engine mounted? Enough air comming in? Any pictures?
Have you checked all bolts?

Do use a Enya 3 or OS 8 glow plug and 5% nitro fuel. Any more nitro is just a waste of money!
Do use a 12-14oz tank and set it up preferably with Uni-flow (two clunks, one for pressure and the other going to the carb).

Doctor Whizz

Looks like the remote needle valve was the problem. Have reverted back to standard configuration as supplied and things are OK.

Thanks for the help guys.