Carb needle jet

[paulfinney2]

I have an 86 R80RT, 80,000 miles, carbs last rebuilt at 30,000, rebuilding again, this time replacing needle jet and needle. Ordered rebuild kit through my dealer, and found the needle jet in the kit did not match the needle jet on the bike or in the bike owners manual.

Owners manual and on current carb - needle jet 2.66
Dealers rebuild kit needle jet number is 2.68

called the dealer, and he [not surprisingly] wasn't familiar with airhead carbs, said he couldn't find a 2.66 needle jet listed in computor, and thought the 2.68 was probably correct because it came with the standard carb rebuild kit. Said it would enrich the mixture some, but not a lot because of only .02 difference.

Comments? Should I just go with the 2.68 or find a 2.66?
Thanks in advance.

86 R80RT
76 R75/6

[AnnapolisAirhead]

called the dealer, and he [not surprisingly] wasn't familiar with airhead carbs, said he couldn't find a 2.66 needle jet listed in computor, and thought the 2.68 was probably correct because it came with the standard carb rebuild kit. Said it would enrich the mixture some, but not a lot because of only .02 difference.

Comments? Should I just go with the 2.68 or find a 2.66?
Thanks in advance.


I'd return it and order from Bing (they'll need the numbers on your carb) or from a BMW dealer. Bing may be a little more spendy, but Maxbmw.com could probably get the right kit. I know Bob's BMW in Jessup, MD has all the right goodies--I just bought mine there because its close and I had a fair number of questions. In the end, even if its a little more, to me, its worth the aggrevation of not worrying about whether or not the source I bought them from knows what an airhead is or not. I doubt that the Germans ever list '...2.68 was probably correct...' in any of their specs. ;-)

Good luck.

[20774]

What is the number on the side of the carbs? This will give you the proper starting point for sizes... I have Bing's book at home, but I'm sure if you called them they'd answer your question over the phone.

Edit: the book says for entries of R80 carbs (the R80RT is not specifically mentioned, also not including the R80GS or R80ST):

2.66 for carbs 201/202, 221/222, 301/302, 321/322, 323/324

2.64 for carbs 305/306

2.68 for carbs 349/350, 353/354

[paulfinney2]

Numbers stamped on side of carbs are 357 [left] and 358 [on right]
Guess I need to call Bing.
While I need to put back in what I took off, what effect would the 2.68 have in stead of the 2.66?
I bought this bike from the original owner, and I'm very certain he did nothing to make any changes. It only had 16,000 mi then.

[20774]

I don't have the Bing book in front of me now...maybe someone can look those numbers up. IIRC, a 2.68 needle will be fatter thus leaning the mixture out for the same clip settings. There could be differences in taper...

It would be good to get all of the settings and jets back to their stock position and then see how the bike performs, check your gas mileage, and look at the plug color. Then go from there.

I remembered/found this page:

http://www.bingpower.com/english/service/einstellblaetter.html

Go down to 64/32/357 and show the data...it appears these are the numbers:

Needle 2.66 (clip position 3)
Main jet 135
Idle jet 45

[88bmwJeff]

I have the same carbs, but on an R100. Bing claims some bikes in the 80s were jetted lean to meet smog emissions, and they sell a rejet kit. Bing incorporated the rejetting when I purchased a rebuild kit. I think the rejetting was incorporated into your kit.

[sumran]

With the mileage on the bike, your current jets and needles you have more than .02 of wear. You will be able to feel the difference between your old needles and the new ones just by running them through your fingers. Are you running rich now? If not, you should be fine with the 2.68 jets.

I recently helped rebuild a friend's carbs. He bought his kit direct from Bing. It came with 2.68's even though the stock jets were 2.66. He has not had a problem with it running too rich.

It is your call, of course. A phone call to Bing might be informative. They will be able to give you the scoop on the difference jets might make in your circumstance.

[sumran]

IIRC, a 2.68 needle will be fatter thus leaning the mixture out for the same clip settings. There could be differences in taper...



:scratch

I believe the 2.66 is the size for the needle jet, not the jet needle. So it is the size of the hole and bigger would be richer. Seems confusing to have two interactive parts named so similarly. I may be mistaken. I'll check the book when I get home tonight. I am basing this on my memory of the stamping on the brass needle jet that sits below the atomizer.

[20774]

I believe the 2.66 is the size for the needle jet, not the jet needle. So it is the size of the hole and bigger would be richer. Seems confusing to have two interactive parts named so similarly. I may be mistaken. I'll check the book when I get home tonight. I am basing this on my memory of the stamping on the brass needle jet that sits below the atomizer.

You are correct, sir!! I really should think before engaging fingers...needle jet or jet needle? They really should have named them differently...

[sumran]

Even a fountain of knowledge has an occasional bubble!:D

[88bmwJeff]

I checked the Bing information when I got home, and they (Bing) suggest rejetting the carbs to a 2.68 needle jet, 48 idle jet, and 145 main jet for the R100 engine. Since you have an R80 engine, I would use the 2.66 needle jet otherwise you could be running too rich.

[paulfinney2]

The information flow is gaining momentum but no definitive answer. I have to be away, but when I get back next week, I will see what this thread has been doing, and probably call Bing.
Thanks everyone for pitching in. We are not done yet.

[Boxerkuh]

Well, an issue that I am working on myself, to continue to strive for the perfect combination.... Is is actually a very complex question and can't be quickly said which one to use. I have been working on mine for months now and have still not hit the perfect combination. Your carbs need to be in good working order and need to synchonized correctly.
The question is what kind of plugs are you running and how do they look. Based on what you are finding, you should only make one small change at a time. Generally speaking, the larger the jet, the richer the mixture, but that is also depending on your needle position. For every 2 needle position changes equals one jet size difference. I have found that running 3 tanks through my bike give me the correct reading. (I have tried it with 1 and 2 tanks, but it is not enough to really see a good reading)
So, for me to help you, I need to know what your plugs look like, what heat number are they and what position your needle is in? Based on that information, changes may need to be made. You may end up with a 2.68 jet. Don't get hung up on the main jet size either, it is insignificant since it is only used when you crack the throttle open more than 3/4 of the way. My food for thought anyway... :eat :drink