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Walbro WA carburettor

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Old 12-04-2018, 10:59 PM
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Jim.Thompson
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Default Walbro WA carburettor

I have a 40 cc Kioritz 40 cc which I am converting to aero application. The plan is to use it in a tug plane.
It has a fuel bowl slide motor cycle style carburettor.
Questions:
1. Will this style of carb be suitable for non-aerobatic type flying? As in aero towing?
2. If not, I will have to try and find a WA series carb. It will also require an adapter as the cylinder retaining bolts are 38 mm between centres.
3. I have had no success in searching for this model carb. Can someone point me in the right direction please?

Some details here: https://www.rcgroups.com/forums/show...Mystery-engine

I am in Australia, but might have to pay some international shipping costs.

Jim.
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Old 12-04-2018, 11:05 PM
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Hi Jim

40cc seems a bit small for aero-towing.

Our tugs have 120cc and the like.

Cheers
Max
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Old 12-04-2018, 11:06 PM
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Old 12-05-2018, 04:04 PM
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I am looking for a chart that was formerly online with all Walbro carburettor specifications etc. I cannot find it now.
If anyone has a link to such a chart, please post here.
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Old 12-05-2018, 04:33 PM
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If you're looking for a new carb for that engine, I'd recommend one of the many WT series Walbro carbs used on similar sized current day RC engines rather than a WA series. The WA series are usually basic carbs with few features and many are not suited for RC use though Zenoah and Quadra did use some WA series carbs years ago. I wouldn't worry about the bolt spacing on the carb as many piston ported engines use a heat spacer between the carb and the engine. The spacer gets mounted to the engine and the carb mounts to the spacer. In some cases the engine will allow for through bolting for the WT series 31mm bolt spacing. Most RC designed engines allow for through bolting but many piston ported chain saw and utility engines do not.

Many Walbro carbs from the new crop of Chinese 20 - 40 cc engines should work and there are many to choose from. Companies such as Mile High RC and Valley View RC offer replacement carbs and show them on their web sites. A very popular and widely used chain saw conversion carb was the WT-76 series and these can still be found new from various vendors. I can give you additional carb numbers if so desired. You will have to know whether the pump pulse port will be internal or external. Most carbs will be internal but it is easy to convert them to external and some are supplied that way.

I see you are in Australia ..... you should have problem finding what you need there. You can still use the American sites for reference.
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Old 12-05-2018, 05:48 PM
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Originally Posted by Truckracer View Post
If you're looking for a new carb for that engine, I'd recommend one of the many WT series Walbro carbs used on similar sized current day RC engines rather than a WA series. ........................................
Thanks for the reply with the good information. I have several WT series carbs in stock.
The spacer gets mounted to the engine and the carb mounts to the spacer. In some cases the engine will allow for through bolting for the WT series 31mm bolt spacing. Most RC designed engines allow for through bolting but many piston ported chain saw and utility engines do not.
.................................................. ....
I have just been going through my drawer full of engine bits. I have carb mount adapter/spacer that can be modified slightly to adapt the two 6 mm studs @ 38 centres down to two 5 mm studs (at 90 deg to the former) to take the WT series carb.
I hope to use some 6 mm "Formica brand" insulating panel that I have for the base that will take the 38mmx 6 mm head stud. This might be too thin, if it is, I can double up. This insulating board is designed for electric power boards.
At this stage, all the above is looking achievable.

The picture is of another one owned by Mike who posted this picture in the other thread. Linked to above.

Thanks again,

Jim.

Last edited by Jim.Thompson; 12-05-2018 at 06:05 PM.
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Old 12-06-2018, 11:43 AM
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Jim Thompson, listen, go to Google, then on the upper right or upper left click on "images", then type in "40cc walbro carbs",,

you will see some carbs in the "size" you need and they will have a standard "straight threw" intake venturi , others in the same size will have a larger intake venturi, in other words the front of the carb is larger than the back of the carb where it mates to the engine,, these larger intake venturi carbs are for higher RPM engines,.. example, my MVVS 35cc Gasser has a larger intake venturi than many 40 cc engines I have seen..

take your time looking, because you can find Walbro carbs for very good prices, I have seen sites selling Walbro carbs for $60 (American) and others site selling the same carb for $32,, be careful because some places sell rebuilt carbs..

also NOTE, that some carbs (like the older carb on the Zenoah g38 ) has a bleed hole on the high needle that will not allow you to lean out the engine to the point you may need..

google images here,,
https://www.google.com/search?q=40cc+walbro+carbs&rlz=1C1CHBF_enUS757US757&source=lnms&tbm=isch&sa=X&ved=0ahUKEwiLrLfY8YvfAhWIdd8KHfMkAXwQ_AUIDygC&biw=1536&bih=754&dpr=1.25

Jim

Last edited by the Wasp; 12-06-2018 at 12:12 PM.
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Old 12-06-2018, 12:58 PM
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Thanks very much Jim.
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Old 12-06-2018, 01:33 PM
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On the photo you posted, there is a glaring error. The crankcase pressure line is connected to the fuel inlet on the carb and the pressure port on the carb cover plate is not connected to anything.
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Old 12-06-2018, 02:25 PM
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Originally Posted by Truckracer View Post
On the photo you posted, there is a glaring error. The crankcase pressure line is connected to the fuel inlet on the carb and the pressure port on the carb cover plate is not connected to anything.
Hey, so it is. Well spotted.
That is not my engine. That is one owned by Mike who posted the picture to assist in identifying mine here:

https://www.rcgroups.com/forums/show...9&postcount=16

Thanks,

Jim.
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Old 12-06-2018, 02:58 PM
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Originally Posted by the Wasp View Post
Jim Thompson, listen, go to Google, then on the upper right or upper left click on "images", then type in "40cc walbro carbs",,

you will see some carbs in the "size" you need and they will have a standard "straight threw" intake venturi , others in the same size will have a larger intake venturi, in other words the front of the carb is larger than the back of the carb where it mates to the engine,, these larger intake venturi carbs are for higher RPM engines,.. example, my MVVS 35cc Gasser has a larger intake venturi than many 40 cc engines I have seen..

take your time looking, because you can find Walbro carbs for very good prices, I have seen sites selling Walbro carbs for $60 (American) and others site selling the same carb for $32,, be careful because some places sell rebuilt carbs..

also NOTE, that some carbs (like the older carb on the Zenoah g38 ) has a bleed hole on the high needle that will not allow you to lean out the engine to the point you may need..

google images here,,
https://www.google.com/search?q=40cc+walbro+carbs&rlz=1C1CHBF_enUS757US757&source=lnms&tbm=isch&sa=X&ved=0ahUKEwiLrLfY8YvfAhWIdd8KHfMkAXwQ_AUIDygC&biw=1536&bih=754&dpr=1.25

Jim
Yes there are many carbs that will work on an RC engine but I would never just buy a particular model number that had not been tested on an RC engine. Some of these carbs lack sufficient metering passages to throttle and transition well in our type of service. Some are perfectly good for lawn equipment but they may work horribly for our applications.

All WT series carbs have the same bolt spacing though yes, their venturi and throttle bore can vary. There are two very common throttle plate / throttle bore sizes (there are more) and these are 14mm and 15.5mm. Common venturi sizes are 24/64" for smaller engines like a 20 and 34/64" for larger engines 30 cc or so and larger. The WT-76 I recommended has the 34/64" venturi and 15.5mm throttle making it a very common carb size. Yes there are other in between sizes but these are quite common on today's engines. The WT-76 was stock equipment on many many engines from probably 26 to 56cc or so mostly in chain saw service and found their way to RC in conversion engines that were so popular in years past. Some of the newer WT carbs used on RC engines have additional low speed mixture drillings and in my opinion throttle better than the WT-76 though the 76 is a darn good all around carb and extremely common. A few years back I installed a Walbro carb from a DLE55 on my older Taurus 52 that previously had the WT-76 and the DLE carb ran and throttles noticeably better than the 76 .... and the 76 wasn't bad!

Lots of choices but I for one don't plan on reinventing the wheel when it comes to carb selection and prefer to use numbers that have been proven to work in RC service.
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Old 12-06-2018, 04:05 PM
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All good and duly noted. Many thanks Truckracer.
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