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I am trying to get a main circuit to quit contributing to the idle circuit. It is pulling fuel when it should not. Trying to clean up the first 1/8 throttle and get rid of the den, den, den, den on decel.  I have lowered the stock needle, jjh, all the way without much change. Trying to decide if I need a major change of the needle jet or go after this with a larger diameter needle. Anybody done this before. Jetsrus has eveything I could need, and needles are cheap, but time means more so helping me narrow the search will help. Again, the question is how to stop the main circuit from contributing to the pilot circuit

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You lower idle speed. If you absolutely for some reason want to completely prevent the needle from possibly spewing any fuel, take a garbage main and solder it closed. But I cannot imagine any reason for needing to do that. I know you have a slide that produces an excessive vacuum at idle and because of that, unless you plug the main, it is going to suck fuel.

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I spend alot of time at near idle. Trials like playing.  I am trying to clean up that area of idle to 1/8. Most riders never spend a second there so it means nothing to them. I have tried slides 3.5, 3.0 and 2.0. The 2.0 giving the best. However I hate the den, den, den of it sucking fuel at 1st gear decel and I hate that the rpm's "fall" when I release the throttle. I want it to shut back to idle at the release of the throttle. All this can be had if it will quit sucking fuel from the main. You can bottom the slide all the way down shutting it's ability to pull from the main and the bike purrs like a crf150. But I need the slide barely open to idle. 

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I just ordered several needles. Specifically the largest diameter offered to fit in the needle jet. Hopefully this will block the main from sucking so bad, but may cause other problems. With the needles I had, I will now have a good variety to experiment with. I assume that the larger diameter will need a faster taper to keep the same top end. Either way, I should have it covered.

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3 hours ago, 1gr8bldr said:

I am trying to get a main circuit to quit contributing to the idle circuit. It is pulling fuel when it should not. Trying to clean up the first 1/8 throttle and get rid of the den, den, den, den on decel.  I have lowered the stock needle, jjh, all the way without much change. Trying to decide if I need a major change of the needle jet or go after this with a larger diameter needle. Anybody done this before. Jetsrus has eveything I could need, and needles are cheap, but time means more so helping me narrow the search will help. Again, the question is how to stop the main circuit from contributing to the pilot circuit

i think you might be chasing a unicorn here 

the only way i can see this to be achievable would be a needle that completely blocks off the main , which in my mind would then require you to run a richer pilot or less air screw  to compensate for that tiny amount of fuel that the main adds at idle or low vacuum , defeating the purpose of the whole exercise

maybe a switch to fuel injection might be the answer for you

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Have had emission tuned street bike carbs act that way. They used a non adjustable needle with a fixed amount of slop in the needle holder that allowed the needle to push up into the slide a hair when it sat into the nozzle.  Down side was slight delay as the slide picked up.   On the old round slide miks a mod was to smooth off the bottom of the slide by filling it with epoxy. At wfo it streamlined the bore for better flow, at idle position it created too much pull on the nozzle which was hard to tune out. We drilled a small hole in the nozzle hood,  to reduce the effect.  Some type 54 bing used a hole right through the slide that was exposed at idle and covered as the slide lifted. It reduced flow under the slide pulling too much fuel.

Edited by highmarker

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6 hours ago, highmarker said:

Have had emission tuned street bike carbs act that way. They used a non adjustable needle with a fixed amount of slop in the needle holder that allowed the needle to push up into the slide a hair when it sat into the nozzle.  Down side was slight delay as the slide picked up.   On the old round slide miks a mod was to smooth off the bottom of the slide by filling it with epoxy. At wfo it streamlined the bore for better flow, at idle position it created too much pull on the nozzle which was hard to tune out. We drilled a small hole in the nozzle hood,  to reduce the effect.  Some type 54 bing used a hole right through the slide that was exposed at idle and covered as the slide lifted. It reduced flow under the slide pulling too much fuel.

I have played much with ufo's and this was my problem as well. Rich on idle. I could compensate by cutting the slide bigger but then it caused a bad lean bog at the fast crack of the throttle. I will one day revisit those experiments because power was great, bog was not. I did not try the hole drilled in the needle hood. 

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I found a longer needle today and set the clip where the needle almost blocked the main. So close to fully shutting it down. The numbers went lean and I did not have anything larger than a 55 to compensate. 

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