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Walbro WT643 L/H Needle Adjustment

falcohob

Heliman

UAE

Hi,

I have been working on my Zenoah G26PUH from a long time and facing the problem in finding the correct high and low needle positions.

I bought this engine in slightly used with JR Voyager 260, when I tried to start it first time I set the both needles at 1-1/4 turns. After priming the carb engine start for just 2 to 3 seconds and die, sounds like just burn the fuel in the card which got in the result of priming and die.

In start my first attention towards the fuel pump and insulator block and found it working fine. Then I decide to change the needle settings. In start engine fired up with more than 2 turn of low needle but its still feel lean, then I open the high needle 1/4 turn. Now the engine refuse to start totally while the low needle was more than 2 turn. Then I close high needle 1/2 turn then engine start and was much rich, I close the low needle about 1 turn. In this setting it looks fine but I canít open the high needle because engine will be lean.

Now I am afraid of engine leaning issue during flight because I canít open high needle to make the engine rich, instead it become lean. I thought the atmospheric air might bleeding from high speed check valve and dismantle to check it but I found it has capillary type high speed jet where the atmospheric air can easily bleed in the metering diaphragm.

12-06-2011 Over year old.
Carey Shurley

Elite Veteran

Orlando, FL - USA

a good place to start is usually 1-3/8 L and 1-1/2 H

if its lean at those setting, its more than likely leaking air somewhere

If you're not flying a gasoline helicopter
You're paying 10 times too much for fuel!!

12-06-2011 Over year old.
falcohob

Heliman

UAE

I started with 1-1/4 both needles but engine wanted to make the high needle close 1/4 turn to start on idle. As I start closeing the high needle engine getting richer and richer accordingly. As I described previously, I am assuming the high speed jet is bleeding atmospheric air thats why the engine doesnít start. To make it confirm I fully close the high needle to stop the bleeding air from high speed jet toward the metering diaphram and start the engine, and its start but very rich and flooded then I close low needle for reliable idle.

Is it normal? Because my carb has capillary type high speed jet not check valve type.

12-07-2011 Over year old.
Carey Shurley

Elite Veteran

Orlando, FL - USA

common things to look at are the regulator side of the carb, I documented what you'll find when you open it up HERE

If you're not flying a gasoline helicopter
You're paying 10 times too much for fuel!!

12-07-2011 Over year old.
falcohob

Heliman

UAE

Thanks Carey, I saw the document and it is very helpful to understand the whole function of WT Carb.
But still after reading this information I couldnít sort-out the issue if its air leakage for any side.
I have checked the carb its looks okay, the possible leakage in my opinion could be from fuel pump side where the crank case pressure in the fuel pump could bleed to the fuel side at the high RPM and mixing with fuel and travel towards the needle chamber. That cans reduce the fuel supply.

I have checked the regulator side is ok and no sign of leakage observe.

May metering needle lever low setting can affect the fuel supply at wide open throttle and when close the high needle valve fully, may that fuel supply for idle circuit is enough?

12-08-2011 Over year old.
Rojoalfa

Senior Heliman

Punta de Mata, Monagas-Venezuela

Spring and ball...where are they?... I miss something...

/
/

Nice job... congratulations... a very precise explanation on WT carb.

Just one question...

Carey, On pic exploded.jpg , you shows a little spring and a ball, near primer body and bulb but I miss something...

Where are they?... they just desappeared!!

/

Saludos cordiales,

12-08-2011 Over year old.
HOMEPAGE  
Rojoalfa

Senior Heliman

Punta de Mata, Monagas-Venezuela


Spring and ball...where are they?... I miss something...

/
/

Nice job... congratulations... a very precise explanation on WT carb.

Just one question...

Carey, On pic exploded.jpg , you shows a little spring and a ball, near primer body and bulb but I miss something...

Where are they?... they just desappeared!!

/
/
/

I got it!... they are the stepper for choke valv... a detent...

/

Saludos cordiales,

12-08-2011 Over year old.
HOMEPAGE  
Rojoalfa

Senior Heliman

Punta de Mata, Monagas-Venezuela

Talking about Inlet neddle...

/
/

Carey, base on your experience, how can I determine if inlet neddle needs to be replace?


I observed this two things on my zenoah 23PUHīs walbro 643:

1.- With throttle fully closed, motor is still running...
It is difficult to shut down this "tazmanian devil".

2.- The Rubber seat tip apparently in good shape... but when you pass a piece of paper, it get "paint" with black... yeah! I khow that this practice is a destructive one...
Using a magnifying glass, I donīt know what to look for!


/

Saludos cordiales,

12-26-2011 Over year old.
HOMEPAGE  
Carey Shurley

Elite Veteran

Orlando, FL - USA

if it still has a rubber tip on it, more than likely it is okay. If this is leaking, the engine will be overly rich

if it runs with the throttle fully closed, you most likely have an air leak either in the isolator are or somewhere on the case

If you're not flying a gasoline helicopter
You're paying 10 times too much for fuel!!

12-27-2011 Over year old.
ttaylor63

Senior Heliman

Floresville,Tx

I have a small engine repair shop close to me. I just take my carb to them and they have a pressure gauge they attach and check to see if the needle and seat is holding.

12-27-2011 Over year old.
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Walbro WT643 L/H Needle Adjustment

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