Technical Discussion => BMW Technical Q&A, Primarily R65 => Topic started by: georgesgiralt on February 05, 2013, 03:04:39 AM
Title: Equivalece between needle clip position and needle
Post by: georgesgiralt on February 05, 2013, 03:04:39 AM
Hello ! There is only one needle available for our Bing carbs. The clips positions are widely spaced. So going from, say 3 to 4, is a big change in richness. Suppose I want to go to 3.5 instead, I could do this by putting the needle at position four and reducing the needle jet size. But what amount ? What size should I select ? Do you know ? It would be greatly appreciated ! Thanks in advance !
Title: Re: Equivalece between needle clip position and needle
Post by: Barry on February 05, 2013, 07:30:48 AM
georges
You have hit on one of the more interesting problems with Bing CV carbs.
The steps between needle positions are much too big in my opinion. I believe one needle position equates to 2 or 3 changes in needle jet size. So changing the needle jet will make a smaller change to the mixture than moving the needle.
Where it gets very difficult is comparing different needle positions with different needle jets and putting them in order of mixture strength. For example: A 2.66 jet with needle position 3 is obviously richer than a 2.64 jet with the same needle position but how do you compare a 2.66 position 3 with a 2.64 position 4 ?
I have seen it done mathematically on a spreadsheet. It involves a lot of work measuring the profile of the needle at small increments along the length of the tapered section. Then you have to calculate the area of the needle and subtract that from the area of the needle jet for each increment. Do that for each combination of needle and needle jet and you can make real comparisons. As far as I know it hasn't been done for a BMW Bing CV but if you are interested I can dig out a document that describes it being done on a Bing carb in another application.
There is another way you can achieve position 3.5 which I have done for my carbs (except I was looking to run at 2.5) and that's by shimming the needle jet height There is the issue of this also changing the jet height relative to the fuel level in the bowl but it does work. You can follow a description of it on a previous thread here http://www.bmwr65.org/cgi-bin/yabb2/YaBB.pl?num=1254577036/0#0
Title: Re: Equivalece between needle clip position and needle
Post by: georgesgiralt on February 05, 2013, 08:07:47 AM
Hello Barry, You give valuable information by saying that one clip change equate about 3 needle jet change. A I want to go from 2.64 and position 4 (too rich) to position 3, I've to get either a 2.66 or 2.68 needle jet. Lucky I am, I own both ! It would be very good to get the BMW part number for the 2.70 or above needle jets, if one has them ! Thanks for your help !
Title: Re: Equivalece between needle clip position and needle
Post by: Barry on February 05, 2013, 08:38:00 AM
Georges
Finding a 2.7 needle jet shouldn't be a problem but I think it would be much too big. You would experience excessive richness at part throttle when the parallel part of the needle was still in the needle jet.
If you really want to try position 3.5 did you consider the shimming method in the last part of my previous post.
Title: Re: Equivalece between needle clip position and needle
Post by: georgesgiralt on February 05, 2013, 11:58:16 AM
Yes, Barry I saw your clever method above ! But machining a washer is too time consuming to be made at night. I've to wait for the week end... I think it should be enough to solve my mid throttle issue with stock jetting. In the meantime, I've tried the #3 and 2.66 and this is not good. So I've switched for a 2.68 and see tomorrow how she behave... It should make a difference from the 2.64 stock... I'll keep you posted !
Title: Re: Equivalece between needle clip position and needle
Post by: georgesgiralt on February 06, 2013, 02:47:17 AM
So I ran the bike under the heavy rain and in the traffic jam to go to work this morning. Seems to appreciate the 2.68 needle jet combined to the position 3 on the needle. So the 3 size of jet to a one clip position change seems to do the trick ! I'm envious to take her to a high speed ride on the highway instead of boring work...
Title: Re: Equivalece between needle clip position and needle
Post by: georgesgiralt on February 10, 2013, 08:25:43 AM
Hello Barry, Yesterday I've found nylon washer to play with. I had to augment the size of the hole to pass the needle jet. alas the washer are 0.9 ~ 1.0 mm thick. So I wonder how to thin them and get a couple of equal thickness... to shim each carb equally. As yet, I've not found a way... So any idea is a good one !
Title: Re: Equivalece between needle clip position and needle
Post by: Barry on February 10, 2013, 10:00:23 AM
georges,
0.8-0.9 mm will give you half way between two needle positions. I found 0.8mm was the maximum thickness that can be used because there has to be some shoulder left on the needle jet to centralise it in the atomiser. Shouldn't be hard to rub 0.1-0.2 mm off on wet and dry abrasive paper.
I originally used 0.5mm thick red fiber washers intending to replace them with brass but I have never needed to as the fibre washers have been fine. They are very easy to rub down to the required thickness.
Title: Re: Equivalece between needle clip position and needle
Post by: montmil on February 11, 2013, 07:45:14 AM
Having once had to "thin" a couple washers, I used wet 100 grit wet or dry secured to a dead flat plate.
To hold those little washers, thin, double-faced tape on a wood block worked well.
Sand in a Figure-8 motion to avoid creating a tapered washer; which I have also once needed.
Title: Re: Equivalece between needle clip position and needle
Post by: georgesgiralt on February 11, 2013, 07:56:32 AM
Hummm ! Seems to be an excellent advice ! Will try it some time this week ! (wonder what kind of sanding paper I've in the garage... )
Title: Re: Equivalece between needle clip position and needle
Post by: tvrla on February 12, 2013, 07:26:21 PM
Hobby stores here in the states carry different thicknesses of copper, brass, and aluminum sheet. I'd be tempted to make my own washers.
Title: Re: Equivalece between needle clip position and needle
Post by: georgesgiralt on February 13, 2013, 12:14:23 AM
Well, I've thought of that, but cutting a 0.3 mm thick sheet to make a circle and an nice round hole in the centre is not that easy...
Title: Re: Equivalece between needle clip position and needle
Post by: Barry on February 13, 2013, 03:10:24 AM
Quote
but cutting a 0.3 mm thick sheet to make a circle and an nice round hole in the centre is not that easy...
We take for granted that mass produced items are accurate to very fine tolerances. Thin washers are hard things to make accurately to the same standards from sheet material. The only ones I ever did successfully were shims for the fork damper valves and that took a lot of time and ingenuity.
Enlarging the existing holes in a washer is only a little less difficult when the washer is so small. I found it very hard to cut clean holes dead centre even in soft material like the red fibre washers. The only way I could do it was to clamp the washer between two sheets of hardwood after first drilling a pilot hole to enable accurate alignment then drill through the sandwich. I still produced as many bad washers as good ones.
Title: Re: Equivalece between needle clip position and needle
Post by: georgesgiralt on February 13, 2013, 03:32:14 AM
Barry, the Nylon washer where with a 5mm diameter hole and sold by the dozen. So I stacked them and drilled the stack while retained between two 6 mm steel washer and a wise grip in the vice... Now, I still have to grind them from 0.9 mm thick to something closer to 0.3 mm in order to be able to adjust precisely the resulting thickness... A last question : What do you think is the maximal outer diameter acceptable for these washer ? I wonder if their presence won't affect air and gasoline passage and so affect the whole air/gasoline mix ?
Title: Re: Equivalece between needle clip position and needle
Post by: Barry on February 13, 2013, 05:41:35 AM
Georges,
The diameter of my washer was slightly larger than the needle jet/emulsion tube assembly but only by approximately 0.2 mm. A larger diameter washer only intrudes into the annular space where the emulsion air enters so within reason I wouldn't have thought it's too critical as long as it doesn't interfere with the air flow. If it was several mm too big I think that might cause a problem.
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Title: Re: Equivalece between needle clip position and needle
Post by: georgesgiralt on February 13, 2013, 07:20:31 AM
Thanks Barry, So I either have to trim a lot the washer I've got or find new smaller washer.....
Title: Re: Equivalece between needle clip position and needle
Post by: tvrla on February 13, 2013, 09:40:56 PM
All this talk about shimming the needle got me thinking about the one's I've measured. You know, when you insert the needles it's best to measure them to make sure they're in the correct groove? I've found that the needle securing bosses aren't set the same height in corresponding slides. I never got the same measurement from one slide to the other.
Looking closely, it appeared to me the differences were in manufacturing. I could see an easy way to adjust the distance - and could even possibly damage the slide, so I left them as is.
But maybe I should re-visit this problem and make a shim for one of them so they're the same.
Title: Re: Equivalece between needle clip position and needle
Post by: Barry on February 14, 2013, 02:39:40 AM
I recorded the needle lengths some time back and even the gaps between the positions vary a little:
I suppose it's possible the reducing gap is deliberate but they don't reduce in a consistent manner. I should check both carbs next time.
Title: Re: Equivalece between needle clip position and needle
Post by: Bob_Roller on February 14, 2013, 01:56:47 PM
georgesgiralt, what method is used to secure the the needle in the slide ?
My '81 has a 6 point star type washer that holds the wire clip that the needle mates with .
My '82 and '84, have a straight slot screw driver threaded plug that holds the needle in .
If you have the latter type, you can add thin washers under the needle to raise or lower the needle as required .
Title: Re: Equivalece between needle clip position and needle
Post by: georgesgiralt on February 14, 2013, 02:03:42 PM
My bike is like your '81. I just checked that the washer was square in the piston and press the spring firmly on the bottom. By the way; would you be so kind to measure the trumpets of the air cleaner cover on your 84 bike ? I would like to know what are the differences from the 81 cover... (see my other topic about the air cleaner cover) Thanks a lot in advance ! :)
Title: Re: Equivalece between needle clip position and needle
Post by: Bob_Roller on February 14, 2013, 02:09:34 PM
I'll check it when I get home, but I won't be able to post until tomorrow morning when I get back to work, my home computer is in for repairs (virus issues) .
Title: Re: Equivalece between needle clip position and needle
Post by: georgesgiralt on February 15, 2013, 11:53:41 AM
Good enough for me. I searched for months someone able to measure them... This week end I'll return the carbs to their stock position. The bike runs rough and no tinkering can help her. Today I rode her a lot, with jets and tools in the pocket. It is really bad. And mileage is very poor. So I'll put back the "plain" standard jetting as per BMW spec, and live with the excessive richness between 3000 and 3500 rpm if I open the throttle fully... Now, I know...
Title: Re: Equivalece between needle clip position and needle
Post by: Bob_Roller on February 15, 2013, 04:25:38 PM
Here's the dimensions of the horns, trumpets, etc......
The large one is 39 mm wide and 25 mm high .
This part had the following numbers molded into it , Purolator LP818-609, a number under a BMW logo, 1337 227 .
The smaller horn has the dimensions of, 26 mm wide and 16 mm high .
Has Purolator LP818/3-609 and the BMW number 1 337 501 .
Both horns are the same length, 136 mm .
Hope it helps out some !!!!!
Title: Re: Equivalece between needle clip position and needle
Post by: georgesgiralt on February 15, 2013, 11:11:36 PM
Thank you very much Bob, I'll try to figure the differences from mine... Yesterday, I saw a mechanic I know at a stop light which is good on old airhead. I explained to him that I had some issues with my jetting. He told me to make a hole as big as I can on the underside of one trumpet to increase air intake at mid range... Told me this has worked fine for many bikes... So now I've something new to try .... Looks like the mode BMW made on the air cover....
Title: Re: Equivalece between needle clip position and needle
Post by: Bob_Roller on February 16, 2013, 07:16:34 AM
Found this for R80 bikes with issues with carbs .
https://www.bmwmc.net/catalog/2120.pdf
Title: Re: Equivalece between needle clip position and needle
Post by: georgesgiralt on February 16, 2013, 09:40:07 AM
Yes, Bob, I know this one. It seems that the filter cover you have on your latest R65 already has the modification. I've tried the same jetting as should have an hypothetical R65 for Europe with the "new" cover with no luck at all. The only difference being the cover. So I tried the bike without air filter. Boy, what a mess ! So I put it back and, yesterday, decided to restore the factory setting for my bike (which I did this morning) and I will live with the "hole" at 3000 RPM. One day, if I find a spare air filter cap I'll try, either the mod with non symmetrical trumpets or make a hole under one of them. This tinkering took me too much time energy and gasoline for a terrible result. In the meantime, I've decided to ride the bike and enjoy my birthday present : a Vinyl apron protection to keep my feet and legs hot and dry ! It is made to measure by a French maker and it's inside is covered with synthetic fur.... Can't wait for bad weather :D
Title: Re: Equivalece between needle clip position and needle
Post by: Bob_Roller on February 16, 2013, 10:21:42 AM
What are the Bing numbers for your carbs ?
They are stamped in the vertical flange at the cylinder head side of the carb, look like : 64/32/325 .
I've got a manual from Bing, that gives the parts that were installed at the factory .
Title: Re: Equivalece between needle clip position and needle
Post by: georgesgiralt on February 16, 2013, 11:54:05 AM
They are 64/32/307 and 308. As far as I know, they are NOT in the bing manual (nor on their Website). As I bought the bike new, in 1984, I have the user manual where the settings are written. (And in 1985 I was able to get the maintenance manual from BMW. A co-worker had a cousin which was a dealer, so he was able to buy it for me !) So I have the settings perfect for 97 leaded fuel.... Now I only get 95 with 10 % ethanol in it....
Title: Re: Equivalece between needle clip position and needle
Post by: Bob_Roller on February 16, 2013, 04:16:42 PM
They show up in the Bing manual I have .
Main jet : 145
Needle jet : 2.64
Jet needle : 241
Atomizer : 591
Idle jet : 45
Needle clip position : 4
Title: Re: Equivalece between needle clip position and needle
Post by: georgesgiralt on February 16, 2013, 04:49:08 PM
Exactly what I have ! Thanks a lot.
Title: Re: Equivalece between needle clip position and needle
Post by: Barry on February 18, 2013, 04:06:03 PM
I've seen several anecdotal accounts saying one clip position is equivalent to 3 changes in needle jet size so I decided I would measure my own 46-241 needles to see if that was true. I calculated the change in flow area for small increments across the full lift of the needle and then compared that with the increase in flow area resulting from a needle jet change.
It turned out to be relatively straightforward to do the calculations as the tapered section of the needle is a simple straight sided truncated cone that reduces from 2.45mm to 1.2mm along it's 23mm length. I plotted the needle diameter at 1mm intervals and calculated the change in area for 1 needle clip position.
The effects are non linear so the answer turns out to be more complicated than just saying it's a ratio of 3 although that is probably a reasonable average at mid throttle. Anyone who has tried it knows that 1 clip position is a big change but the flow area change turned out to be a lot bigger than I expected.
My factory settings are 2.66 needle jet and needle at position 2 so that is the base line for my comparisons as shown by the green column in the table of figures and graph attached. A summary of the results is as follows:-
Increasing the needle jet from 2.66 to 2.68 results in a jet flow area increase of 10% at initial lift reducing to 2% at max. lift
Likewise reducing the needle jet from 2.66 to 2.64 results in a jet flow area reduction of 10% at initial lift down to 2% at max. lift
Lifting the needle from P2 to P3 results in a jet flow area increase of 44% at initial lift reducing to 5% at max. lift
Combining a 2.64 jet with needle in position 3 still gives 34% increase at initial lift falling to 3% at maximum lift,
Base data for the calcs:-
Needle Dia 2.45 Tip Dia 1.2 Cone length 23 2.64 jet Area 5.47 2.66 jet Area 5.56 2.68 jet Area 5.64
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Title: Re: Equivalece between needle clip position and needle
Post by: georgesgiralt on March 03, 2013, 03:58:10 PM
Hello ! Today I've made a mad discovery... I took the bike on a long trip (I normally use it to go to work, 8 km long trip) to test my fork after some work on it. I was very surprised to encounter a very poor behaviour even when the bike had fully warmed up after 20 km. She had the same problems I had when trying the jet setting of a post '83 bike ! So I came back home thinking it could be a problem with the ignition. I took the timing light and was unable to make it work using the right spark cable as a trigger. So maybe all my trouble trying to get her running properly with the settings I try to devise for 95-E10 (95 gasoline with 10 % ethanol) were caused by a bad ignition cable... So stupid.... I thought the problems I had today could be : bad timing; clogged fuel lines; dead spark plug; Octane far too low or too lean (way too lean). So as the timing is good (up to max advance), I'll try another cable tomorrow.....