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Left Side Fat at Idle
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Gonzodog
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Joined: Nov 23, 2005
Posts: 8

PostPosted: November 23, 2005, 4:52 pm    Post subject: Left Side Fat at Idle

Folks, I need some advice. Here's the scoop:

'81 650 Special II, 3,100 total miles (I believe it too). Stock carbs/air filters/exhaust.

Right side: 42.5/135/FS @ 3 out - beige color on plug

Left side: 42.5/135/FS @ 2 out - black & fluffy on plug

It likes to load up at idle. When revved after idling for a couple of minutes, it blows some black smoke out the left pipe. Right side - no smoke.

I've sealed the intakes between the carbs & head. The carbs are squeaky clean inside and all passages are open as far as I can tell. Jets are all open - nothing plugged. No varnish inside. Slide diaphragms are intact. Carb boots are intact. New Yamaha air filters 100 miles ago.

Valve clearances just adjusted in spec. Compression 155 both sides. Carbs synched. It starts and runs fine. Throttle cable is loose at idle setting. Idle on the tach shows about 1200-1500 RPM.

Both floats (replaced w/new from MikesXS) are at 22mm ( manual shows 27.3 but no way to get 27.3 w/these floats. The new floats are exactly like what came out of the bike.

It has acted like there is a vacuum leak as it wants to hang at a high idle (2500) sometimes, but not always. I have not been able to locate any vacuum leaks.

Any ideas as to the cause of the hanging idle and black left plug?

Suggestions on places to look for vacuum leaks?

Why rich at idle?

Thanks for your help!

Jim
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Breneau
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Joined: Apr 04, 2006
Posts: 1

PostPosted: April 29, 2006, 12:05 am    Post subject: Re: Left Side Fat at Idle

I had a similiar problem on my 71 XS1B. Took it to the dealer and they messed w/ the carb, increased the idle but did not fix the problem. Took the bike home for the summer (college student) had the old man look at it, and he traced the problem to the left coil cracked and not providing proper spark. Not sure if you have two coils but sounds like the same problem.

Bob
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jayel
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Joined: Apr 16, 2006
Posts: 3417
Location: SE Iowa 1974 TX650A

PostPosted: April 29, 2006, 3:26 pm    Post subject: Re: Left Side Fat at Idle

if you have the starting enrichener on that side make sure it isn't holding open, a dried out rubber in the bottom of the lift valve will have you running choke full time resulting in rich mix on that side jayel
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mo650chopper
WebMaster
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Joined: Mar 13, 2005
Posts: 544
Location: Lonedell, Missouri

PostPosted: April 29, 2006, 8:11 pm    Post subject: Re: Left Side Fat at Idle

I'm betting jayel nailed it with the choke on the offending carb. Although On my 80 model I had to run both carbs idle screws maybe a 1/2 turn at most open to not be too fat at idle.
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