Triumphrat

ohiorider · 03-21-2008

Is there a mileage where these two parts should be replaced? I'm getting ready to rebuild the Bing CV carbies on my Beemer. I was reading over various rebuild articles, and found that a couple of rebuilders recommended replacing mains and needles since they wear because of the constant movement of the two parts against each other. The result is that the mixture begins getting too rich. Any thoughts about our Keihins?

Bob

Normandy · 03-21-2008

It would take a pile of miles to wear them babies out but I guess everything wears or fatigues over time eventually.

Jimbonnie · 03-21-2008

How many miles are on the set you're rebuilding?

Now, if I recall correctly the main jet sits at the bottom of the stack and never makes contact with anything. Logically, you'd never have to replace a main jet other than for tuning. The mid range jet is the one the needle slides in and out of, so those should bet the wear items.

You could always compare a new needle to the used one and see if you can measure any differences. Another way to know if you should possibly change these parts, and probably the most reliable assuming everything else is up to snuff, is if you experience a decrease in fuel mileage. And of course you can always just change them because it's reasonably inexpensive and that way you'll know they've been renewed. As long as my bikes deliver 45 or so mpg, and they always have, I haven't ever bothered to replace jets or needles.

If you've never rebuilt a set of Bings it's really easy to mix up the enricheners or reassemble them incorrectly, so it's usually best to do one side a time. There's a punch mark on the enrichener shaft to help you get it right.

If you're planning on replacing the butterfly shaft o-ring, which is usually not necessary, remember that the butterfly has four possible ways of going on the shaft but that only one is correct. The butterfly is marked with a small punch mark so that can help, but it's probably best to mark the outside top or bottom so you're sure to get it right. And you won't be able to remove the butterfly mounting screws without destroying the shaft without filing their ends off; for some reason I continue to try on occasion and it never works.

666Bonneville · 03-21-2008

i've got a '73 bonnie with a ton of miles. and the needle and main jet don't need replacing.

i think the thought of how they wear and should be replaced is a theory based on speculative thought. i've never met a bike that needed those replaced because of wear.

ohiorider · 03-21-2008

Quote:

Originally Posted by Jimbonnie

How many miles are on the set you're rebuilding?

Now, if I recall correctly the main jet sits at the bottom of the stack and never makes contact with anything. Logically, you'd never have to replace a main jet other than for tuning. The mid range jet is the one the needle slides in and out of, so those should bet the wear items.

You could always compare a new needle to the used one and see if you can measure any differences. Another way to know if you should possibly change these parts, and probably the most reliable assuming everything else is up to snuff, is if you experience a decrease in fuel mileage. And of course you can always just change them because it's reasonably inexpensive and that way you'll know they've been renewed. As long as my bikes deliver 45 or so mpg, and they always have, I haven't ever bothered to replace jets or needles.

If you've never rebuilt a set of Bings it's really easy to mix up the enricheners or reassemble them incorrectly, so it's usually best to do one side a time. There's a punch mark on the enrichener shaft to help you get it right.

If you're planning on replacing the butterfly shaft o-ring, which is usually not necessary, remember that the butterfly has four possible ways of going on the shaft but that only one is correct. The butterfly is marked with a small punch mark so that can help, but it's probably best to mark the outside top or bottom so you're sure to get it right. And you won't be able to remove the butterfly mounting screws without destroying the shaft without filing their ends off; for some reason I continue to try on occasion and it never works.

Jimbonnie - The Bings have 110.000 miles on them, and have only had the diaphragms replaced once. Everything else is original. Re the 'main' jet, I called it the 'main' as a point of reference for the Bonnie riders, since the needles in the Keihins do contact the mains. But you are correct about the Bings. The needle doesn't touch the main jet, but does move thru the one that is above it. I'm considering having the ace wrench at Mathias BMW rebuild them. He's done dozens of sets of Bings over the past several years, and their hourly rate is far lower than larger shops, especially low for a Beemer shop. I've asked them to quote a complete rebuild including the seals around the butterfly shafts, new floats, float needles, gaskets, etc, etc.

BTW thanks for being concerned enough to respond with the Bing info. If I was doing it myself, you certainly emphasized some good points.

Bob

Jimbonnie · 03-21-2008

Bob, I'm glad you pointed out the differences between the BMW and Triumph carbs because we want to stay on Jeff's good side by always including Triumph twin content.

"The Bings have 110.000 miles on them, and have only had the diaphragms replaced once."

Well, if any carb had worn parts needing replacement parts I'd think yours was a good candidate. At that many miles I'd also replace the contact parts, just because.

The work you've mentioned shouldn't take more than an hour per carb if you bring them to your mechanic reasonably clean (it's a good idea and a nice gesture). Bing parts you'll find are expensive.

But hey, your Beemer's still good for a few hundred thousand more miles before you have to do anything really expensive, and so a few hundred dollars to sort out the carbs is cheap in comparison to a replacement bike.

Have you thought about buying a set of the Triumph carbs that occasionally come up for sale in the classifieds of this website and installing them? I'll bet they're a close fit, require only minimal tweaking to get right, and they're sure less leaky than sixteen year old Bings.

Jim

dkreidel · 03-21-2008

My two '66 Bonnevilles and my '68 have original needles and jets - and are in perfect shape. I've owned the '68 since new, so I know for certain they have never been touched.

Dick

Jimbonnie · 03-21-2008

Bob's needle and mid range jet might not be worn either, but at least those two parts are cheap so replacing them won't hurt nearly as much as the floats, diaphragms, float needles, and other parts will.

Me, I'd check the fuel mileage and make a decision from there, but I'm notorious about getting every last mile out of each and every part. But whatever makes Bob happy works for me too. It's kind of like treating the old nag to a new pair of horseshoes, even if the old ones aren't completely worn and falling off just because she deserves them for such long and faithful service.

bendavanza · 03-21-2008

On the old Amals, the 106 needle jet wears out quickly from the needle hammering it. This make s the bike run rich.
The needles get beat up, too but the main jet should need nothing but a cleaning once in a while.
New carb designs should wear better but have the same shortcomings.
-Ben