question about bdc carb series

[david a luciani]

Hi Guys,

Especially Steve O'Hara (hint,hint)

if you guys could,i'd like the general breakdown of the bdc carbs.
by that i mean a list of the various numbers and whether they were single or double pumpers.
i know that bdc 14's are singles and i thought that bdc16's were doubles.
that's the extent of my knowledge.

the reason i'm asking is that i am going thru my pile of mcculloch carbs and rebuilding a few.

i hadn't checked their numbers but i noticed that the fuel inlet was considerably bigger on two so i looked at the numbers and they were bdc16 and bdc22.
so it seems i have several that are stamped bdc16 or 22 that are set up with single pumpers.
is this normal or a distant mod that was done for unknown reasons?
thanx dave

[Jeff Campbell]

Right from 1979 IKF tech manual, since this is dated after the last Mac engines were made, this should be a complete list of BDC carbs that were approved for use at the end of the McCulloch era.

100cc single pumper carbs: BDC-14, BDC-14A1, BDC-22A, BDC-22A1, BDC-23

125cc double pumper Alky carbs: BDC-16 and BDC-24


I have BDC-24 carbs with mfg dates on them of 10-74 and 04-76. The BDC-24 carbs with 04-76 dates were the ones that came stock on the last MC101B motors made.

the BDC-22's and/or 23's may have been carbs that came on the MC91 m/c motors? (I am just guessing here).

Jeff

[steveohara]

David,

Jeff's info looks correct to me but I have to admit I have never seen either of the "A1" versions.

In general, the there are two carbs, the BDC 14 gas carb and the BDC 16 double pumper alky carb.... the rest of the model #s represent very minor variations usually dealing with the type of throttle shaft and the inclusion of a choke lever and butterfly.
Otherwise, the important dimensions that determine the way the carbs work are all identical.
As you described, 30+ years of bouncing around has produced all kinds of combinations of parts from the different models so you never know what you have unless you match the parts to the original tech specs as you can find on this site.
Steve O'Hara

[Rick Chapman]

Dave,
Because I prefer the single pumper carb on my 100cc engines, I will take a double pumper carb and replace the double pumper plates with the single pumper plates.
There are still plenty of new complete rebuild kits available for the 101AA type double pumper carbs available. Ben Ray Griffith, Griffith Specialties, has them (540.269.4111)
I do this because I am unable to locate any of the Hi-Speed Products Zip Kits.
Than I make my personal modifiations to the carb so it will flow alky correctly and these carbs then work perfectly.
Rick

[Bill Johnson]

A lot of the BDC 14 and 22 carbs had their Needle and seat replaced with a bigger one back in the day to run Alky like the BDC16. I am not sure who made the kit but it may have been Chuck West. Little did we know back then that it was really the pump that couldnt keep up and not the flow of the needle and seat. Heagar had the Mystery Clutch and I think the BDC carbs classify as the Mystery Carbs back then. They are really better than a Tilly if you take the time to fine tune them but that takes a lot of trial and error these days and expensive rebuilt kits.

[Ken Ploog]

I have recently found a carburetor marked BDC16 in the mass of parts I acquired. I've read here that it used for 100cc McCullough engines on alcohol...My question is can this carb be used for gas on a slightly larger engine ?....A modified Predator 212 to be exact.

What are the fuel and air requirements for a carb this size?
Are there jets I would need to change to switch it over to racing gas?

[Rob Voska]

If you are going that route I would go with a HR series Tillotson. Much easier to get parts for.