BSA B50 replacement carb

Kneepuck · Dec 29, 2013

Hi all.
I have a 71 B50 that has a cylinder head modified to accept a japanese carb. The throat is 30mm i.d. The flange bolt holes are 2 7/8 in. center to center. Has anyone a recommendation for a carb? Amals dont work without ovaling out the bolt holes. A flat slide would be okay, or anything really.

Thanks in advance

Kneepuck · Dec 29, 2013

BTW, this bike is getting a makeover. The carb that was on it is trashed. It is also getting a Boyer electronic ignition, a Boyer battery eliminator , and a replacement 150 watt stator for the lucas. New rings, stock pistons and some paint will see it through. I hope.

thanks again

motoracer8 · Dec 29, 2013

I have a B50 with a 32 mm Delorto on it, it works fine. I use a adaptor that uses the std flange size.

Kneepuck · Dec 29, 2013

using an adaptor would open up the possibilitys, for sure, except there isn't much clearance for the frame. I reckon I'll get out the calipers again and check that. Thanks

Time Warp · Dec 30, 2013

The JRC (Keihin) 30 mm flat slide carburetor has a fairly good reputation and is reasonably priced.
That mount spacing seems wide though. (Most JRC kits have Amal spacing when using the flange mount)

http://www.jrceng.com/gallery/JRC-PWK-c ... -in-action

http://victorylibrary.com/brit/jrc-c.htm

Allens have manifolds.

http://www.allensperformance.com/produc ... folds.html

Kneepuck · Dec 30, 2013

After checking the measurements again, i found that I had measured wrong and the throat is 32mm. I like the idea of the flange, as the head no longer has studs to mount the carb, just threaded holes. A carb with a flange built on would be tough to mount without replacing the studs, and there is room, albeit not much, for the carb to fit. I will be thrilled if this works, because I have 2 of these bikes. I envision getting some friends to help, and riding both of the b50's, the Triumph 650 and the Matchless to the local weekend bike hangout and watching all the Harley riders scratch thier heads in confusion. What fun!
Thanks for the help

Kneepuck · Jan 16, 2014

As a follow up, I did order two Mikuni 32mm carbs, as well as the adaptor flanges , for both. The first is on, and running great! I never heard either of these bikes idle so well, or start so easy. ( First kick, believe it or not ).

Amazed does not even begin to describe the way that made me feel.

Triton Thrasher · Jan 17, 2014

Kneepuck said:
.....B50..... Boyer electronic ignition....... a Boyer battery eliminator......

Oh my ankle!

Kneepuck · Jan 17, 2014

Ha ha, I know what you mean. I used to have to get 5 or 6 of my dumbest friends to come over and help kick the things. But, I find that, even with the battery eliminator, if I still use a battery, it starts right away. Plenty of spark.

Kneepuck · Jan 29, 2014

Here is a couple pics of one of the B50's. It is in rough shape, missing carb, wrong coil, missing points plate and advance, etc. But the engine turns over freely and has good, surprisingly good, compression. The rest can be dealt with. I'm encouraged because the other one came out so well.

Kneepuck · Feb 10, 2014

Hi all,

I have hit a rather major snag in the resurrection of the '73 B50. While replacing the stator, I discovered that the primary chain tensioner was broken. Upon closer inspection, I also saw that, because of the broken tensioner, the primary chain was able to slap the base of the top stator mounting tower. It is cracked off right flush with the case.
I dont know about the feasability of welding this, as it is, I believe, cast aluminum and would be beyond my welding skill. I hate to replace the case, because then I dont have matching numbers. Also, I have been unable to source a new case. Anyone have any suggestions?

Thanks in advance.

Kneepuck

baz · Feb 13, 2014

Kneepuck said:
Hi all,

I have hit a rather major snag in the resurrection of the '73 B50. While replacing the stator, I discovered that the primary chain tensioner was broken. Upon closer inspection, I also saw that, because of the broken tensioner, the primary chain was able to slap the base of the top stator mounting tower. It is cracked off right flush with the case.
I dont know about the feasability of welding this, as it is, I believe, cast aluminum and would be beyond my welding skill. I hate to replace the case, because then I dont have matching numbers. Also, I have been unable to source a new case. Anyone have any suggestions?

Thanks in advance.

Kneepuck

this is quite common to snap off an alternator pole on one of these BSA motors ,whereabouts in the world are you? if your in the states send it to Ed Valiket if your in the UK send it to Mark at PES performance CCM specialist regards baz

Kneepuck · Feb 14, 2014

Ah, many thanks. I am in the states, California.

franknbott · Apr 18, 2014

Hi Kneepuck, I have a 1971 B50t and would be interested to know what model MIKUNI carb you used, and what jets are in it as I am a 79 year old, I need an easy start , hope you can help I live in Australia, regards Franknbott

Matt Spencer · Apr 19, 2014

Sounds like you need a belt drive primary . :shock: Welding case for any competant head shop COULD be no bother ( alloy heads these days ) IF you could find one .

better tried & true . and trusted .

Did I tell you about the C.C.M. 608 MX back in 74 . . . . :x :wink: :lol: Saw him put the throttle on down the top straight ONCE :shock: easy 80 mph with the bespecticaled bank clerk astride .

:wink:

Kneepuck · Apr 19, 2014

I used Mikuni VM32 , 32mm carbs on both bikes. I cant tell you the jet sizes, I just left them stock. I also had to purchase the intake manifold flanges as well. It was a bolt on job. And works great on both bikes. Cold starts are , clear the cylinder with a couple kicks with the compression release pulled in, choke on 1 kick, choke off, 1 kick, started. Usually....

Kneepuck · Apr 19, 2014

Just to update, I had a friend who welds aluminum all the time do the repair on the broken tower. A few minutes with a file cleaned up a little extra material left and the stator bolted up nicely. I purchased an aftermarket primary chain tensioner which worked, but I had to grind a bit of it away to get the stator to be able to seat properly. I'm happy to report both B50's running strongly, all mechanical issues resolved. It is true that the Boyer battery eliminator, or as they (more accurately) refer to it as the Power box, will start the bike without a battery, but with a lot of kicking and cursing, especially when cold. However, I acquired, at $22.00 us each, 2 - 12 volt gel cel very small batteries. They provide plenty of juice to get the bikes started easily, and are easy to fit. They can be installed in any direction you want, though I have them upright. Now for the cosmetic side.....