Carburetor OK but old.....what to do?

[suecanada]

Just wondering what your opinions would be regarding LRB's carburetors which so far have been metering out the fuel very well. I have replaced the diaphrams and the float bowl gaskets. Nothing else has been refurbished. (1983 bike with 87,000 miles). I am suspicious that I may be silly not replacing or at least carrying with me some needle jets or whatever. Opinion needed: refurbish the carb internals on general principle of old age OR carry along on a trip the most likely parts that would fail...say like the floats?

Please tell me what parts I should get as every time I go to Bing or to Bob's BMW catalogues I get confused as the Bing repair kits seem to just include the diaphrams and gaskets..maybe floats. How can I tell what else like size of float needle?

[Justin B.]

I think the Bing book might break down the needle and jet sizes, the BMW HTK database I have just lists part numbers.  As long as your fuel mileage has not significantly changed then I wouldn't get paranoid about changing the needle and jet as they wear out slowly - not fail catastrophically.  I have, though, heard 35k miles tossed around for a change interval.  

It might not be a bad idea to pack along a couple of floats, though, as gasoline starts getting higher and higher percentages of ethenol.  When I head out on a trip the carb related items I take are floats, diaphragms, and some fuel line.

[Bob_Roller]

Sue,

You need to get the Bing numbers off of both carbs, they are on a vertical flange on the front of the carbs, numbers should be something like : 64/32/335 and -336.

Then you can get the proper replacement parts from Bing.

I just replaced everything on my carbs, I would say all of the rubber seals need replacement, along with the needle jet and the needle itself, as well as the float needle valve.

This would include the much feared throttle shaft o-rings.

Along with a good cleaning.

[trolle]

Sue, when you unscrew the two small screws fastening the butterfly or throttle to the shaft be very careful, that you do not ruin the screws or their seats.

On the upper half of the butterfly or choker  there is a little spot made with a center punch, which is easy to miss. Be sure that you can see the spot in the right place when you replace the throttle.

When you fasten the screws again do not tighten them before your are absolutely sure that the throttle is seated properly at the walls of the duct: If you place a clear source of light at the other side of the throttle, you should in principle not be able to see the light around the rim of the choker. Due to wear a little light might slip through though. When satisfied fasten the screws with a very small drop of Locktite.

It is easier than it sounds!

Another thing: When you place the diaphragm be sure that it is seated correctly in the groove.

When you take the carbs apart, do it in the kitchen and be sure to have a strong light and an uncluttered table.

Take a look at http://www.tannis.dk/bmw/Diary-6.htm to see the innards of a carburettor.

greetings from a grey and quiet north

trolle

[Ed Miller]

Here's my favorite carb rebuild article:

http://home.insightbb.com/~cdpumphr/the_carb_chronicles.htm

On a more serious note regarding the throttle butterfly plate screws:  the ends protruding through the shaft will have been squished down to keep them from backing out.  Its easy to use a narrow file through the bore of the carb and file the protruding ends down flush with the shaft, then the screws should back out OK.  Everything in there is so soft that I don't recommend a dremmel type tool like some articles suggest.

[Justin B.]

If you plan on replacing the throttle shaft O-rings then you will need to order replacement screws for the ones Ed mentioned that you would need to file down.  But, I contend that if her fuel consumption hasn't went south, carbs sync up nicely, idles and runs smooth, then leave everything alone!  Conventional wisdom indicates that the main jets and needles should be worn out but if they were the fuel consumption should have increased.

Of course, all of my speculating and laziness is out the window if Sue is just looking for an EXCUSE to rebuild her carbs!

I re-read the carb chronicles every few months and still laugh my butt off...

[Bob_Roller]

My fuel mileage dropped about 6-7 mpg, and the needle jet was quite worn, it was worn in an oval shape.

The screws holding the butterfly, or throttle plate, can be troublesome, one set came right out after filing down the 'upset' screw shank, the other one, must have been peened by someone with 'issues', as I filed off all of the expanded metal, and they refused to come out.

I ended up stripping the threads out of the throttle shaft, but if you do damage the threads, don't get real upset over the fact, as the throttle shaft is about $12US.

Also be mindful of how the throttle plates are installed, as they have a tapered edge, and the upper half is tapered opposite of the bottom half.

[trolle]

I re-read the carb chronicles every few months and still laugh my butt off...

Have just read the chronicles and was overwhelmed with fond memories:  [smiley=huh.gif] [smiley=furious3.gif] [smiley=idea2.gif] [smiley=vrolijk_26.gif].

BTW what is the rationale behind grinding those two small screws down?

greetings from a grey and quiet north

trolle

[Justin B.]

The proper way to install the "butterfly" screws is to support the head and then "peen" the opposite end to expand/deform it so there is no way it can accidentally back out.  That's why if you remove these screws without grinding the end off you run the risk of screwing up the hole in the shaft - it's almost like running the next bigger size tap through.  I have used some screws (Holley carbs come to mind) that had a little "dimple" in the end of the screw that allowed it to expand/deform easily with less force.  I think this is pretty much the standard SOP on all carbs and throttle bodies.

[Bob_Roller]

The screws from Bing are a very soft iron based metal , I 'peened' the backside with an automatic center punch, 5 or 6 applications of the punch, and the screws were deformed enough as not to be concerned about them ever coming out on their own.

[Justin B.]

I'll have to try the sprin-loaded center punch next time, sounds like it should beat the hell out of trying to hold onto everything while operating a punch and hammer at the same time...  [smiley=mad.gif]

[Bob_Roller]

I ran into that issue when I went to peen them, and I didn't like the thought of beating on throttle shaft.

Even though, the 'brass, or bronze' material that the shaft is made of is a lot harder than I would have thought.

It may take a few more clicks with the automatic center punch, as I replaced the spring in mine to a heavier one, as I was working with stainless steel at work for a while, and the standard spring wouldn't leave much of a mark on stainless steel.

[Justin B.]

I made a fixture to mount Holley and Quadrajet carbs in while I peened the screws but on the Bings I have done my wife graciously lent the "third hand".  I have a few of the el-cheapo Harbor Freight auto-punches and they have pretty stout springs so I'll try one next time.

[trolle]

.. That's why if you remove these screws without grinding the end off you run the risk of screwing up the hole in the shaft - it's almost like running the next bigger size tap through.  

I KNOW!!!

greetings from a grey and quiet north

trolle