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Shimming needles/popping

  • Thread starter Thread starter Rein
  • Start date Start date
R

Rein

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So I put on the new carb boots on the 650gl, and now drops in idle about as fast as it goes up, however, it hangs just a tiny bit at 1500 before dropping to 1200. It also pops when dropping revs, which leads me to believe it's lean. Mixture screws are set at 2.5 turns out (Then adjusted using highest idle method), stock airbox, stock pipes. Valves are adjusted, carbs squeaky clean, runs great, except for the popping.

Would shimming the needle help a little? What size of washer do I need? No radioshack, so I'm not sure what size it'll be. I have a home depot, Ace, and various hardware stores, but would like to get the right size on the first trip. I under stand it richens the bike a little, but how does it do this?

Would increasing the mains a bit help?
 
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If it runs great at wide open throttle then your mains are likely right (stock should be good for your setup!)

Yes it might help to shim the needle up a bit, the needles were set lean from the factory....

Do a search on the washer, pretty sure it's been listed here or crack the carbs & take one of the plastic washers with you to Ace & have a hunt through their hardware bins...

Dan :)
 
I'd say, ride it a little, maybe 5 - 10 miles, then come back and look at your spark plugs. They'll tell you if you need to adjust the mixture screws in (lean) or out (rich). Only turn the mixture screws a tiny tiny bit at a time in either direction. Because at this point as close as you probably have it, a tiny bit will make a big difference.

But I'd say do what your spark plugs are telling you to do.

Other's will be along that knows way more than me about it to help you I'm sure.
 
You may want to richen your mixture screws a tad, try 3 turns and see if this helps the popping. Shimming the needles can't hurt. I used #4 washers and turned them down to the OD of the plastic spacer that was originally on the needles.
 
almarconi said:
You may want to richen your mixture screws a tad, try 3 turns and see if this helps the popping. Shimming the needles can't hurt. I used #4 washers and turned them down to the OD of the plastic spacer that was originally on the needles.
Click to expand...

I agree with this post.:D

For the washers, if you find the right ID, stack them on a screw and then add a nut and cinch them down. After that stick the screw into a drill motor and spin them while taking a file to reduce down the OD to the size needed.
 
Rein said:
Would shimming the needle help a little? I under stand it richens the bike a little, but how does it do this?
Click to expand...

To answer your question, shimming the needles with washers will raise them, thus allowing more fuel to pass through the jet needle circuit a little bit quicker because you've raised their initial set point. You should notice a difference in mid-range acceleration & the "flat" spot should be gone...

The key is to REMOVE that little plastic spacer and REPLACE it with a stack of washers that measure smaller than the plastic spacer. By doing this, you are "raising" the needle by the amount of difference measured between the "washer stack" & the plastic spacer.

For example, your stock plastic spacer most likely measures approx. .100" thick. If your washers each measure .025" thick, and you use 2 of them, you will have raised the needles .050". Use 3 washers and you raised the needle .025".

Measure your plastic spacer and use a washer stack that will raise your needles about .040" - .050" to start. See how it reacts to that.

BTW, you don't have to remove the carbs to mess with the needles - just remove the fuel tank & you should have enough access to remove each carb top to pull the slides... just be carefull when you put the tops back on to make sure the diaphrams are seated correctly in that little groove.

Good luck,

mike
 
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Popping on overrun can be an exhaust leak. Radio shack sells washers that worked on my 1100 G. I had a hard time finding a snap ring plier that would go up in the slide. I ruined one set trying to modify it to work.
 
850 Combat said:
I had a hard time finding a snap ring plier that would go up in the slide. I ruined one set trying to modify it to work.
Click to expand...

A cheap pair of needle-nosed pliers work well. Just grind the tips a little to fit into the snap ring holes... all good.
 
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