juance

Hi guys:

I am experiencing a weird problem with a 3W 75 US installed in an Extra 330. Whenever I go from normal position to inverted the engine gets richer. This happens with throttle not full.

Any clues.

Thanks in advance !!!


JC

rc bugman

My Feedback: (30)

Hi,

It this the rear carb version or the side carb version? How do you have the engine mounted? inverted?

Elson

juance

Yes it is side carb, mounted inverted.

JC

kfir2

I have the same problem with a 50i and asked the same question on 5/20/07 see page 14 on this forum. Nobody has given an answer. At a local show when talking to Iain Nicols of IAD Designs he said it was the spring on the diaphragm that works the demand needle that is weak. He suggested streching the spring. Another manufacturer (i cant remmember who but somewhere on this site) suggested lenghtening spring 2mm to overcome the same problem.As my problem suddendly got unbearably worse I am in the process of getting a carb kit as needle may also be worn. Also have a look at geistware.com aircraft proving grounds do it yourself tips about walbro tune up and pop off pressure or aercorsair. Much luck

rc bugman

My Feedback: (30)

It sounds like you need to slightly lean the mid-range by leaning the lower end needle. With the engine mounted inverted, excess gas is spit out the intake and when you roll inverted, all the fuel goes into the engine.

Elson

juance

Kfir2: I will definevely try what you told me, but first I will try what Elson told me about leaning the mid-range.
Thanks to both of you.
I'll let you know how this work.

JC

flynbrian

My Feedback: (1)

There needs to be a vent coming off of the diaphram cover going into the fuse (for a constant pressure).
Just take the cap that covers the diaphragm and solder a hollow tube, then just run a line into the fuse.

Hope this helps
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ram3500-RCU

My Feedback: (221)

My new 3W55 started the same thing. I leaned out the low end a little over 1/8 turn.....better but still did it some........then the high end a heavy 1/16 turn. Fixed, and gained some RPMs as well.

ram3500-RCU

My Feedback: (221)

Update. Just flew my 3W 55 again today and I tweaked the needles again. I was still getting just a little drop off when rolling to inverted (thought I had it all out). I had to close them both just a tad today. The low end is now open 5/8 turn and the high needle is just under 3/4. Excellent transition, smooth steady idle, and tons of power at the high end. I'm convinced this phenomena is carburetor adjustment related now. At least it was for me.