Carburetor Queries PUH231 WT 643

[Brian18]

Hi All

I have a problem with my G231 PUH carburettor a WALBRO WT-643.
When the fuel screws are fully screwed in - the priming bulb pumps fuel ok and it works normally.
When the fuel screws are at the factory settings from the manual a whistling noise can be heard when priming and the bulb pulls air from somewhere.
The carburettor is not working.
I tried PTFE plumbers tape on the screws to try to stop this whistling noise because I thought it was pulling air through the screws but it made no difference at all.



**Some history to clarify**
I constructed the heli according to the plan but I fitted the carburettor using a sliver of liquid gasket during construction at the mating faces.
I had been having problems setting up the engine after the running in period was complete which progressed to having difficulty getting fuel to the engine once the throttle opened beyond the first third of travel (Approx) and so I stripped the carburettor to check it out - since I suspected the problem was related to a blockage at the high speed needle I found that some of the liquid gasket had migrated behind the diaphragm and so I cleaned and stripped the whole unit and put it all back together again but it doesn't work now.




Any advice would be appreciated.



Rgds



Brian

[Billme]

Something that I have learn since running the Radikal 20 is the carb just never give a problem so long as the fuel is filtered good.. It doesn't have a bulb...Got along just fine without it...
With the 30 i done the same thing, went to a 257 carb.. It has no bulb as well, and it runs even better... atomizes the fuel much better, much easier to tune..

Lesson learn, i stay away from the those bulbs...

The frame can crack, the check valve can leak, they can play havoc with you...So I do without them, when fueling up the first flight, I just put a little fuel on the screen of the airfilter, and the fumes light off the engine on the first pull if you have everything tune good.. One less factor to deal with.....

Since you have this stuff all in your carb, you probably have it in areas where you can't get too... You can try sonic cleaning, but i would just get a new carb..
Good luck
Bill

[fastflyer20]

From your description, it sounds like it is starving for fuel

A few ideas:

Can you explain your plumbing of each line? One line looks like a filler and one a vent. Venting is critical and will react the way you describe if not properly vented. If the big silver one toward the bottom is a vent, try removing it and just attach the line up high to test.

Are the gaskets attaching the carb and manifold correctly oriented to allow for the pulse signal? The pulse hole is what moves the diaphragm to pump fuel.

The primer is not needed, you can replace with a solid plate.

[Brian18]

Thanks Billme

I may need to take your advice but can't seem to source one.
The nearest supplier for the repair kit is in the states.
I've been googling this issue and I can see that you have been busy on the forums with these carbs already.
I also seen an earlier posting on a site pointing to faulty non return valves.
The thing is if I need to pay most of the way towards a replacement carb to import a repair kit then I'll get a complete unit.

--
fastflyer20 Thanks for the reply

Three lines from the tank one copper line directed internally upwards to vent it is the one hanging down and fixed to the landing skid.
One fuel feed line with petrol clunk pick up (Soft type).
One fuel return/filling/emptying line with petrol clunk pick up (Soft type) the filling part goes up then down tied to the vent line.

The fuel feed line has one double Sullivan filter fitted then direct to the carburettor.

The t-piece is a 3 way filter on the return to tank from carburettor and fill/empty line. A stopper is fitted to the open end from the t-piece on the fill/empty part. There is a non return valve / filter nearer to the carburettor (Upstream) and it blocks fuel back filling when filling the tank from the T-piece.

Fuel feeds and pickup lines are all ok without air in the lines or restrictions.
Separately my fuelling system is littered with filters so the fuel is passing through clean; too and from the heli.

The fuel lines are all ok. I was using this setup prior to stripping the carb.

Youre right about the fuel starvation the engine was being starved at the change over into the high speed part of the throttle curve. I stripped it and cleaned it but have the problem with the air in the bulb. When I fully close the slow fuel jet screw and high speed fuel jet screw - the fuel pumps around the lines correctly.


Regards

Brian

[Brian18]

Hi Folks

Can anyone advise me on the most suitable carburettor for my Zenoah engine and a supplier where I can get it.

Originally Posted by Billme

Something that I have learn since running the Radikal 20 is the carb just never give a problem so long as the fuel is filtered good.. It doesn't have a bulb...Got along just fine without it...
With the 30 i done the same thing, went to a 257 carb.. It has no bulb as well, and it runs even better... atomizes the fuel much better, much easier to tune..

Lesson learn, i stay away from the those bulbs...


Since you have this stuff all in your carb, you probably have it in areas where you can't get too... You can try sonic cleaning, but i would just get a new carb..
Good luck
Bill

I have a problem where my Carburettor is not working properly and I would like to source a replacement unit. I have tried various things to rectify the problem where the priming bulb pulls air when the needle screws are open and it pumps normally when they are fully tightened. I can't see anything obviously wrong with the carburettor.


The Heli is a Radikal 30 and the engine is a stock Zenoah G231PUH
fitted with a; WT-643 carburettor / Zenoah part# T2077-81000
Is the 257 suitable for the stock 231 motor?

Thanks for any advice.

Brian

[MotorRotor]

Originally Posted by Brian18

[COLOR=black][FONT=Arial]......When the fuel screws are at the factory settings from the manual a whistling noise can be heard when priming and the bulb pulls air from somewhere. .....

Could the air be coming from somewhere else?

I and others I know have many hours logged on our Predators and Radikals using that same carb and no such issues.

[Brian18]

Originally Posted by MotorRotor

Could the air be coming from somewhere else?

I and others I know have many hours logged on our Predators and Radikals using that same carb and no such issues.

I have removed the carb from the engine with the fuel lines attached and blocked the holes with my fingers where I can. I thought the air was pulling either;
at the engine pump pressure vacuum hole,
from the side of the bulb support plate or,
perhaps more likely from the jetts I couldn't access these properly and It is difficult to pin it down, but by removing the carb I have elimenated the insulator and gaskets.

I have noted 3 small holes inside the choke and also a slightly bigger one which I couldn't access properly. I am assuming some of these are the jets and that a non return arrangement is in place which is either damaged by my poking around with a small paperclip or clogged by my liquid gasket. I suspect that if this is right then the carb is probably a right off and so I'll just replace it.
The other likely possibilty was a problem at the gasket near the bulb but I can't see anything out of the ordinary there either, when the needle screws are tight it pumps fine and the return line one way valve is working ok. Gaskets and non return flappers are all looking ok.

The lesson here is probably don't poke with paperclips and don't use liquid gasket around the sealing faces, I still don't understand how it got inside but I think it was in there non the less. Another possibility is that what I am thinking was gasket material may have been 2 stroke oil that has somehow curdled inside causing the jets to allow flow both ways.



Eitherway; I suspect I have damaged the carb or, don't understand the problem well enough to find a proper solution. So- it goes in the too hard box.

I've decided to just replace the whole unit as the repair kit is unlikely to improve matters.



Regards

Brian

[Billme]

Get new gaskets... The stock gaskets are good for maybe two installs....

One thing you can do is take the carb to a local small engine shop.. Most will know the Walbro.. they can do a couple of test, and will probably have a kit that will fit since most of the carbs use the same kit..

You may have to go to a few shops before you get someone that can help you...

The 257, 990, are good choices if you have to replace the 643, but you can always get another 643...

[Brian18]

Thanks Billme

I'm going with the 644, new gaskets and also a replacement insulator.
No point in checking the carb further as I found a file on the web that showed the design.
I'm almost certain that the non return valves in the jets are damaged and passing since that is the logical coclusion for the bulbs effectiveness being determined by the needle positions.

Cheers

Brian

[Brian18]

Originally Posted by Brian18

Thanks Billme

I'm going with the 644, new gaskets and also a replacement insulator.
No point in checking the carb further as I found a file on the web that showed the design.
I'm almost certain that the non return valves in the jets are damaged and passing since that is the logical coclusion for the bulbs effectiveness being determined by the needle positions.

Cheers

Brian

Just got flying yesterday (Hovering) as it was my first chance since the last post above I still need to tune up the engine.

As well as the change to the carb and sealing bits, I've changed over to fully synthetic 2T Castrol oil as well.

Thanks all for your advice and dennisP for your great help.

PS. Motorotor It was not a slight on the carb - I still think that the issue I had was most likely due to the 2 stroke oil clogging up (Curdling) from sitting unused over a month in the carb or the liquid gasket may have got inside somehow and it was worsened by my poking around with a paperclip and damaging the jets.

[MotorRotor]

Originally Posted by Brian18

......PS. Motorotor It was not a slight on the carb - I still think that the issue I had was most likely due to the 2 stroke oil clogging up (Curdling) from sitting unused over a month in the carb or the liquid gasket may have got inside somehow and it was worsened by my poking around with a paperclip and damaging the jets.

Yep, a dirty screen can also make the engine run very erratically. let's hope you now have it all sorted.