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Wren 44 acceleration problem.

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Wren 44 acceleration problem.

Old 04-23-2010, 04:13 AM
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Boomerang1
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Default Wren 44 acceleration problem.

Hi Guys, I'm having a problem with an early, manual start 44 accelerating.

The engine will accelerate to about 120,000 RPM then run rough, flame out & belch smoke.
The problem has been getting progressively worse but I have been increasing the accel. delay
to overcome the problem. Now the delay is so long (50) as to be unacceptable.

If I open the throttle verrrry slowly it will run up to full power at 190,000 rpm & decelerate o.k.
Starting is also faultless.

Any ideas? I have a spare engine with all accesories so I can mix & match to fault find. - John.
Old 04-23-2010, 05:19 AM
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Default RE: Wren 44 acceleration problem.

If it was ok before then it is not a setting on the ECU more likely the pump or blocked needles
Old 04-23-2010, 09:48 AM
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Default RE: Wren 44 acceleration problem.

I have contacted Mike Murphy in England on this...more than likely a partially blocked fuel ring.
Old 04-23-2010, 12:00 PM
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Default RE: Wren 44 acceleration problem.

Ron,
In other posts, you mentioned that too much oil (5%) can cause a blocked fuel ring in this engine. Could this be a possible cause? I ask because I have fuel mixed for my Mk III that I plan to use for my 44. If you find out that this is the reason, can you post it here?

Thanks
Old 04-23-2010, 12:13 PM
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Default RE: Wren 44 acceleration problem.

The higher percentage oil usually results in a condition where the bearings seem to be "sticking " after cooldown.

The early 44 motors have a bit smaller needle and are more prone to blockage.

If the motor is on the bench....run some clean kero thru the fuel line, you may get lucky.

It is not a hard job to upgrade the motor...but it should be done at the factory.
Old 04-23-2010, 07:32 PM
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Default RE: Wren 44 acceleration problem.

Hi Ron, thank you for chasing this up.

I am running 5% oil, the reason being my Super Sport's bearings (and other owner's Supersport bearings) sounded noisy to us & Mike suggested upping the oil to 5% to see if it made a difference. Run time on these engines is low.

I questioned if it would cause problems in my 44 & the reply was it may cause slightly more combustion chamber coking with prolonged use but otherwise no problems.

I take it a blocked fuel ring requires a complete strip down & rebalance? - John.
Old 04-24-2010, 10:25 AM
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Default RE: Wren 44 acceleration problem.

Chamber and fuel ring replacement does not affect balance!
Old 06-05-2010, 11:06 PM
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Default RE: Wren 44 acceleration problem.

Problem solved!

Removing the engine to send it back to Wren for repair I noticed two of the rear screws missing, not the ones that hold the nozzle on but the ones in between that sit nearly flush.

Fitted a couple from my 'spare' engine & it's now running fine.

Now the pieces of the puzzle fall into place. Quite some time ago the engine statred flaming out on acceleration so I increased the acceleration delay to make it accelerate ok. [sm=confused.gif]This may have been when the first screw fell out. It ran, with slower acceration, for a while then after a few succesful flights at Wangaratta jets it all of a sudden had acceleration problems again, when the second screw fell out, I'm assuming letting case pressure escape. [&o]

Can anyone tell me what the factory setting for acceleration delay for the first Wren 44's is? With the screws out it would not accelerate at 50, I had it down as low as 10 today but it stumbled on acceleration, a little less stumble at 15 so it's now at 20 & ruuning smoothly. I can live with that spool up time.

Thanks for your help & put it in your memory bank. - John. [sm=wink_smile.gif]

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