rubber-tipped BS38 float needle answer

Maybe a bit of crud got under one of the needles.

There's a pretty simple, fast, and non-messy bench test. Carbs upside down on bench. Cap-off one fuel inlet nipple. Attach one end of a hose to the other nipple, put the other end in your mouth, suck to create a vacuum, and hold the vacuum with the tip of your tongue. You should be able to get a strong vacuum and hold it indefinitely. If this test fails, you can narrow it down to one needle or the other by taking one of the needles out and pressing a finger over that needle seat to seal it, and repeating the test. If you take both needles out and press your fingers over both needle seats and you still fail the test, that means one of your needle seat sealing washers is not working.
 
Had a couple sets of rubber tip needles around. The 70 weathervane has been stumbly rich. Plugs were sooty black. Pulled carbs, as usual when the carbs are off a couple changes happen. Needles had wear rings, seats were quite new. Marked 2.0. Put in the rubber tips, one side pretty much a direct swap. Other side had to lose the washer and work float tang some. :shrug: Set both floats at 25. Also dropped needles from 3rd to 4th groove AND did this.
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added a washer above the clip so the plastic pill acts to hold the needle in place. Needle can still move cuz pill is held by a spring.
One petcock was leaking so R and R'd, was polishing the lever when the buffer grabbed it and sent it flying. Spent two hours cleaning and neatening area round buffer. Finally found the lever 10 feet away. Removed paint from under petcocks, sealed new paint edges with crazy glue.
KIMG3746.JPGKIMG3749.JPG
Did head retorque (badly needed) Couple other loose bolts, put it back together. Couple hours of cleaning, polishing. Put in gas, turned on petcocks. Turned around for a minute and gas pouring out. Shut off gas, started it leak stopped. All good now. 10 miles, no leaks running much better and plugs look happy.
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Spent some time syncing throttles.
Came back after an hour sitting with the petcocks on, no drips.
Happy dance.
Oh yeah, throttle shaft seals too.
Took it out again and night n day difference. If it had been running this well, I would have ridden it to the Ozarks rally
 
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I've "tightened" the needle up in those older slides like that as well. Without the shim washer, there's a lot of up-down play and "slop" in the needle, probably a good half MM. That would allow the needle to change it's height by about half a needle clip position while operating. I figure it would go lean on acceleration (needle drops as slide rises) and rich on deceleration (needle rises as slide drops).
 
I've "tightened" the needle up in those older slides like that as well. Without the shim washer, there's a lot of up-down play and "slop" in the needle, probably a good half MM. That would allow the needle to change it's height by about half a needle clip position while operating. I figure it would go lean on acceleration (needle drops as slide rises) and rich on deceleration (needle rises as slide drops).
All true, I think reducing how much that needle is shaking should reduce wear on jet needle and needle jet too, and they are about irreplaceable.
 
Wasn't happy when weathervane went back to it's old ways after a couple rides.
just ordered these from Nichecycle,
View attachment 245948
reports when they're installed and used.
Installed These and the 70 is running great, not rubber tipped. The seat threads were slightly longer than the mikunis, but they went in and flowed gas fine. they came with fiber washers that I used. Setting floats was easy, no extraordinary tab bending needed. While I was in I dropped pilots from 45 to 42.5
After an oil change will run up a few miles on it today then drain the fuel and wait for the shipping company to show.
 
Talking of jetting, do any of my UK forum members know a good place to find new pilot and main jets for my 650b's bs38's?
 
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