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I played around with the Idle adjusting Screw when the bike was running rough and now it won't start.
How do you reset the idle adjusting screw back to a starting point at which the engine will start up again and then adjust the idle from there?
 

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Try turning it half a turn at a time clockwise till it starts. Also using the choke may help


Zee
2000 Triumph Thunderbird Sport
2010 BMW F650GS
 

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I don't quite understand how the idle adjustment screw would stop your bike from starting. Basically all it does is raise or lower the rest for the pivot arm on the carbs that the throttle cable attaches to. As Zee9 pointed out, giving it a little choke helps, but thats just richening the fuel mix. So you tried that but it did not work. Did you try cracking the throttle a bit? That has the same effect, but also opens the slides as well. If richening the fuel mix doesn't help, then maybe your not getting enough air flow? I.E. maybe the idle adjustment setting is at it's lowest and the crab slides are basically shut? I don't know, but it's a guess. When I rebuilt my carbs, I replaced the whole idle adjustment screw assembly as the rubber/plastic covering was melted, the knob itself was melted and the whole thing wouldn't turn. Put the new one on and spent a bit adjusting it to get the level set. Ended up being way too high and my idle was over 2000+ grand. I fixed that. I could see the slides and the throttle arm, as I went to K&N pods (they were off), so if your using the stock air box, it might be harder to see what's going on. I could look down between the 2nd and 3rd carbs and with a small mechanic's mirror, could see when it touched the throttle arm, etc...

In this warm humid weather, I've noticed my bike has a low level buzziness to the idle. Runs like a champ at highly open throttle settings, but gets buzzy at low throttle settings and sometimes just won't hold an idle. I was just playing with my idle adjuster today at the stop lights and I seemed to have sorted out the idling (raised it a tad). Before it was doing that un-even 3-cylinder lopping that I like, so it may have been too low. (I don't run a tach so I can't tell unless by ear or hook up an external tach). So I was thinking the humid, hot air was messing with the mixture. Previously I've been doing Zee9's trick and cracking the choke a bit to start and keep it running until it warms up (it's 95+ outside, how cold natured are these beasts?) Now I tried leaving the choke off, and just crack the throttle a couple of times, then blip it now and then. With the idle adjustment I did on the way home, it seems better. In the cold though, it starts and runs great.
 

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How do you reset the idle adjusting screw back to a starting point at which the engine will start up again and then adjust the idle from there?
Remove the primary airbox, back the idle adjustment screw all the way out until the throttle butterflies are fully closed, then slowly wind the screw in until the butterflies start to open. You need about .5 mm gap.

Although I don't think it will help as your first sentence indicates that it was already having problems before you started fiddling.

To help with debugging these problems, more background info is needed. IE has the bike been standing for a long period, have you recently purchased the bike, elaborate on "running rough", how much fuel is in the tank, have you tried switching to reserve etc'.
 

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Discussion Starter #7
Thanks for the info. Here's some more background on the bike. I have owned the bike since 1998, it was always a great runner but in the past few years I have used it less and less so it stands for longer periods of time now. I should have a run schedule to keep things primed and ready but my work keeps me from doing this. The bike stood for almost a year when I tried to get it running again and it needed a battery and new starter.
I put a Denso starter in it, changed the spark plugs, drained the old gas and replaced with a fresh gal of non-ethanol gas and it fired right up but was very rough and discovered it was running on 2 of the 3 cylinders. Then winter came and back the bike went into the corner of my garage until this summer. I took it out of storage this week and started messing with it, trying to get some signs of life out of it, it starts to fire but dies.
Well, that's where I'm at now with the bike.
 

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First thing I'd do is check the plugs, that could show you which cylinder is having problems - ie black & sooty, wet, totally bone dry and no colour etc'.

My next step would be to check the airbox for blockages (I sometimes stuff an old sock in the airbox inlet to keep bugs & stuff out over winter and forget to remove it before starting! Also make sure both hoses are still connected and the drain hole (bottom hose) is blocked.

Then I'd pull the carbs and give them a good clean out. You might find that the fuel has jellified in one or more float bowls and need a good clean out, pay lots of attention to the idle jets, all galleries, and especially the o-rings & springs on the idle screws.

And don't forget the "duckbill" filter and if possible it might be worth draining the tank and pulling the fuel tap out to check & clean. There's a sieve filter in there that gets blocked occasionally.

Good luck & happy hunting :).
 
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