Originally Posted by
the Wasp
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.