Bing Help

[jagarra]

OK ran into a couple of issues. I have the slide out, diaphram remove, how do you get the needle out, do not see any method of how to release at pin, clip or whatever. Also no spring between the top cap and the slide, pictures I have show one, were they missing on some models?????

Did the butterfly before I read your comments, all went smoothly, didn't peen them yet. Guess secret is to support from behind, have a very pointed peener and catch just the edge of the treads to flair out a bit.

[Garnet]

On the early carbs the needles are held in by a spring clip. Turn the needle a quarter turn (by hand or with a rag covered pliers) while pulling down. It will click down. do that a couple of times and it will pop out. Later ones are different, and I am not sure if it is a clip or set screw, but should be obvious.

Don't peen those screws yet. You want to make sure that the butterflies are back in their proper location. You may want to reinstall them on the bike and make sure that the idle is correct and then remove them and peen away. PITA I know.

[jagarra]

Thanks for the info on the needle. Went to Snobums' site and found the info on the needles. I know the butterflys are correct as I marked them before I took it apart. If you match the camfer on the edges it only seals in one direction. Strange about the lack of springs, on Snobums site he talked about different springs and did provide a couple of part numbers (yeah!!!) Ordered both sets of numbers just now. Funny, the fiche for the bike showed the springs ,but no number in the parts list. Bad sign there.

Besides ordering new needles and everything else I could think of I got new floats, he sure goes on about them in his article. Weighed them and the old ones were pretty good 198gn vs 186.4 for the new ones. even the diaphrams were looking good. Gonna change them anyway, since I am doing one carb at a time, no telling what I will find in the other one.

thanks,

gg

[georgesgiralt]

Hello !
The spring above the slide make it looks like it is heavier. So it takes more vacuum to raise it. This change the ratio of the mixture on variation of throttle. (as the depression rises, the slide does raise fast as there is no spring and the mixture gets enriched sooner).
I can't tell thousand miles away if it is good or bad on your bike. So if I where you, I rebuild the carbs with the BMW planned settings (jets, needle position, with or without a spring) and see how she handle.
And go from here changing ONE thing at a time and monitoring closely the gas mileage ... Bear in mind that today fuels are not the same as they where when the bike left the factory so you will have to twiddle a bit...
The bike will be smoother with everything new inside and this will be a satisfaction by itself !
As per the butterfly, I unscrew the idle stop screw and close the butterfly with the two screws not tightened. This helps the disc settle in the barrel. And then I tighten the two screws, then peen them. And return the idle stop screw to the standard setting BMW told you to use in the manual.

[chasbmw]

My r90/6 suffers from surging at low speeds/ closed to low throttle openings, my rebuild of the carbs neglected the butterfly spindle O rings, it has been suggested on the UK owners club forum that replacing them may cure the surging, so this is a job on my winter therapy project list.

[chasbmw]

PS
Jag area, you early 90/6 would not have had slide springs fitted from new.

I fitted a pair of the later ones to my 90/6 to see if that would cure the surging (see post above) but they made it worse.

I had the bike dyno tested last week and this did show a leanness spike at between 2000 and 2500 revs and it is possible that new O rings might provide a cure

[jagarra]

Charles, thanks for the clarification on those springs. Another new issue, changed the needles to day, tried to get them even with the measurement of a vernier caliper, best I could do was within .010 of each other, no matter which ever way I went when it fell into the clip the distance was too great. Guess that is close enough??
Saw there was a washer between the main jet and the housing, is that washer to help even up the variance between the needles??? Like on the shorter needle length add a few thousand under the jet to add a bit of richness??

[Garnet]

I have never taken the time to measure the exact length of the needle/clip height. I just hold the two pistons needle to needle to make sure both needles are in the same clip position.

.010 difference is not a big deal. There are all kinds of differences on the left and right side of your bike. The air tubes are different shapes, one has oil in it, unless you have a crank trigger ignition, you will have a different spark on each cylinder, they will run at different temps depending on the wind direction, and the list goes on.

[georgesgiralt]

Hello,
The washer at the base of the main jet is to even the petrol supply to the jet. If you look at the bowl you'll see there is a round ridge at the center of the bowl quite the same size as the washer. Do not forget to put the washer back ...
I'm far from accustomed to Imperial measures, but if you set the two needles at the same click stop it is IMHO good enough. The slight difference, if there's one will be taken care off by the extra setting of the idle screw or idle mixture. (there is also a tolerance on the needle jet diameter, main jet hole diameter, etc... )

[jagarra]

OK,I will leave them as is, maybe swap them between each other to see if the issue is in the piston. I was doing some comparisons on the old needle, they appeared to be unequal from the end of the tip to the first grove. One of the carbs didn't have a washer under the main jet, I did order a new set, had to go to the fiche to see where that part number went when I was digging out the bits from the box of stuff. The bike should run great after the rebuild, the idle jets were completely blocked, packed solid with gunk. Had to carefully use a gas welding tip cleaner as that was the only really small strong wire I had. May use the new diaphrams I ordered, they are the same thickness, but a different color, a grey rather than black. Really surprised it ran as good as it did. Not much chance of a ride though, SNOW.