OS 55 AX losing power - Page 2 - RCCanada - Canada Radio Controlled Hobby Forum
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Old 07-24-2019, 09:33 PM   #11
aspeed
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Re: OS 55 AX losing power


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With it running at least half throttle put your finger over the exhaust outlet to richen it and or flush crap through the needle assembly, or at least see if going richer will cure it. Wear a glove.
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Old 07-25-2019, 08:16 AM   #12
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Re: OS 55 AX losing power

From your description and checks I would still think you are suffering from a fuel restriction that shows up only at full demand.

Here are what I would go through if had it here:

Remove the filter and go direct. Reason is to remove as many connections and/or restriction points as possible.

Remove the tank and pull the insides. Check for the obvious, but also anything blocking the clunk input. If you have one of the filter style, discard it for a normal brass style. The external filter will suffice and you want to make any items like that external and easily serviced. If a brass clunk check the diagonal slots cut into the end each side of the inlet. If blocked and the clunk rests against the tank wall it can restrict flow.

Check and remove any sharp ends on the brass tubes. When cutting to length the ends can become extremely sharp and some brass fold over to block the tubes. The sharp external edges can cut the inside the of the silicone tubing and form a flap, a sort of check valve inside the line that may block full flow. It may also only occur when flow is enough to make it fold inward so will not show at lower rates.

Take a piece of tubing and blow into the carb inlet fitting. As the throttle is opened you should hear considerable increase in flow. If not you may have a physical restriction in the inlet or fuel bar, again, only to show up at max flow requirement. One thing you can do is to remove the HS needle and try and flush anything out onto paper towel or rag.

Worst case, if none of this works go back to basics such as checking and resetting your needles, tank padding and prop balance. The second can cause agitation and aeration of the fuel, aggravated by an out of balance prop or loose engine mounting. Did not mention if you see any bubbles in the carb feed line so something else to look at.

Oh, yes, what prop are you running?

I would offer to go through it and run it up on the test stand to see if I can find your problem, but with the distance that would be time consuming and costly for you, especially in the middle of the flying season.
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Old 07-25-2019, 03:38 PM   #13
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Re: OS 55 AX losing power

Not sure if mentioned..... remove the spraybar And high speed needle and poke arround with a fine toothpick to see if any dirt in the spray bar. Had a friend with a similar issue and found dirt in the spray bar tube the size of a match head. Removed that, flushed it with fuel and problem solved. Flushing before using the toothpick to loosen the dirt, did not help .
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Old 07-25-2019, 06:01 PM   #14
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Re: OS 55 AX losing power

Again thanks all for the feedback.
Thanks Cougar for the offer but indeed we are a bit far away.
Besides, I like a good challenge.

I did a blow test in my 2 AX55 equiped aircraft and really I dont feel the sick one to be more restrictive.
I did at one point removed the needle valve so am wondering now if something did get out and maybe it is back to normal. Will try to restart the engine this weekend and see if something changes.

Must say that this tank is not a recent install (about 3 years) and has been good since day one. Only the engine was changed this year.

Prop is APC 11x7
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Old 07-26-2019, 08:40 PM   #15
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Re: OS 55 AX losing power

Finally, the engine is back on track!

While preparing the engine for a test run, I noticed that the pressure line coming from the muffler was looking somewhat funny, like there was a cut in it.
Can't say for sure I saw a cut but after replacing that portion of the tubing with a good one, engine ran fine at full throttle without an issue.

So problem fixed.

Thanks for all the help.
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Old 07-27-2019, 06:04 AM   #16
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Re: OS 55 AX losing power

There ya go. Sometimes it's the simple things.
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