ASP .52 throttling problem

[vijaysagart]

I have a 52 ASP engine which is giving me a lot of problems, especially when i transition from idle to top speed. The engine starts easily, but when i throttle to full, bubbles come in the line between the primary needle valve and the carb. Sometimes, the engine sputters and then picks up, then no bubbles come. I tried everything possible, replaced all the fuel lines with fresh silicon tube, but the bubbles in that part still come. Then I slipped a sleeve of silicon needle over the high speed needle valve, thinking that the bubbles are getting in from there. But they still come. No bubbles at idle speed, no bubbles at high speed, but bubbles are present when I throttle from idle to full. those bubbles make the engine lean, it sputters around, sometimes it picks up, sometimes it just dies. Then I read that maybe the tank is vibrating and creating bubbles, but the bubbles are not in the main line from the tank till the high speed needle. Am at my wits end now. Can some experienced guru shed some light on this issue please. Will  be most grateful.

[flyingboxcar]

Do you have another ASP 52? Or an OS 55? Try replacing the needle assembly from another 52 and check. Similarly if you have an OS 55 the carb should fit in the 52. If you don't have one, borrow one locally
That will tell you if the problem is with the needle assembly or the installation of tank and the lines

[sanjayrai55]

Check your tank also. Possibility of loose or worn bung, or of some problem in the internal lines eg the Aluminium (or brass) tube may have a pinhole. Is your clunk fitted correctly? Have you packed the tank in foam rubber? Else vibration from the engine may cause frothing in the fuel

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[sanjayrai55]

Also a possibility of a pinhole in the primary carb assembly

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[saikat]

best is try with another similar main needle assy

does it happen when you transition very gradually ?

if not available then try

richen low speed needle
richen high speed needle.

use positive pressure on the tank vent line

[vijaysagart]

Thank you all for your replies. I think i will try out with a OS 46 needle. It is fitting nicely. lets see what happens. will post my observations soon.

[vijaysagart]

Hi all. thank you for your replies. The ASP 52 problem has been solved, mostly due to your inputs. I replaced the ASP needle valve with a Needle valve from an old beat up OS engine. I changed the glow plug to a idle spray bar variety. No more bubbles. And superb transition from idle to full out, does not even skip a beat even after idling for 3-4 minutes. The engine itself is a beauty, what power. thanks folks. Happy flying.

[flyingboxcar]

Good to hear that and good on your part to update on resolution. Most people do not update. The update helps others who may come looking for similar information.

[sanjayrai55]