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Old 05-02-2012, 11:05 PM   #1
QatarRider OP
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Question Ural Keihin Carb idle

Hi Fellow inmates.

My lovely 2007 Ural is fitted with Keihin carbs. I've cleaned and fiddled with them many times, and they now run reasonably well, but the engine takes ages to go from half or full throttle to idle. As a result the engine is still reving high on changing gear (see previous thread). I dont think there is anything wrong with the diaphragms, and she does idle given a few seconds. The butterfly valve is shutting quickly, so it's not sticky cables or weak springs and the overrun bypass hole is clear.

I'm thinking that the diaphragm needs a bit more downforce to make it shut off quicker, maybe replace the springs, if these are known to go weak, or double them up?

Any ideas would be much appreciated

Rob
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Old 05-03-2012, 03:49 AM   #2
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Get a can of ether (starting fluid) and (VERY CAREFYLLY) spray it around areas near the carb to check for vaccuume leaks. (at idle, it will raise rpms slightly if there is an intake leak)

Ps. I don't own a Ural (yet) but I am researching and saving $ over this next yr. to make it happen so, I'm reading all Ural threads as much as possible.
I figure the basics are still the same for trouble shooting.
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Old 05-03-2012, 04:14 AM   #3
Brendan J
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As the previous poster mention it sounds like you have a vacuum leak. This could be caused by intake manifolds that have gone hard and dont seal properly where the carb slips in or it could have a small crack in the manifold or leaking around where the manifold bolts to the cylinder head.
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Old 05-03-2012, 09:19 AM   #4
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wd-40, or berryman B-12 will safely find vacuum leaks, not sure I would use ether
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Old 05-03-2012, 09:33 AM   #5
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If you find no air leaks, it could be that your idle is just set too high. I've had the same problem until I figured out that the idle speed needed to be reduced, this seems to be a rather fine adjustment. Once the jetting and pilot screws are properly set, I find the idle speed is set about right when, from a cold start, you need to hold the throttle open a little for about 30 seconds as the engine warms. After that, the idle will be a bit low, but once up to temp, the RPM increases until it's just right, and will make shifting a lot nicer as the engine doesnt hang at hi RPMs.
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Old 05-04-2012, 04:56 AM   #6
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Quote:
Originally Posted by crampfan View Post
wd-40, or berryman B-12 will safely find vacuum leaks, not sure I would use ether

F.W.I.W. I use Berrymans' B-12 about once a month with my gas to help keep the engines rings clean and it's also a lot cheaper than Seafoam for helping clear out dirty carbs.
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Old 05-04-2012, 02:47 PM   #7
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Absolutely rule out the air leaks first, especially on the fitting between carb and head.

Next most likely suspect is as earlier stated, the idle is too high. The ignition advance kicks in pretty early so it wants to keep going. I've seen this with a couple of Ural owners that haven't been around enough other Urals to hear "normal", I guess it's the lack of tachometer.

Another possibility is the idle jet being too large. This of course wouldn't happen spontaniously, but we didn't hear the full history.
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Old 05-05-2012, 11:07 PM   #8
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Cheers guys, I'll check out the inlet leaks first. I did find some tension in the cables, which made a difference and she was running a bit high on idle on this mornings run in to work. One thing at a time, I'm getting there!
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Old 05-06-2012, 09:45 PM   #9
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All is happy and bright!

As so often, a number of things, a loose inlet clamp on the starboard carb, the idle was a bit high as well, then I checked the idle mixture screws, set by the local mechanic, they were way out, set them both to one and a quarter turns, reduced the idle, balanced the carbs with one of those gadgets, and lo and behold, a really low idle, and much quicker to drop to idle on changing gear, so everything is good.

It was a pleasant 35c on the trip in this morning, and no one tired to kill me, so no road rage.

And the coffee is good!
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Old 05-07-2012, 09:08 AM   #10
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Nice!
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