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Old 11-20-2010, 03:14 PM   #16
Craig in Alabama OP
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update

Hi Folks,
Well I did some experimenting today. I rechecked the choke assembly and I can't see anything wrong. The float level is about the same in both bowls (15mm or so). I compared the idle jets and they are the same (4.5) and I swapped them, hoping the problem would switch to the left cylinder. But it did not! Dang!
It's still idles highest with the mixture screw all the way in (right cylinder only).
So I went for a ride anyway. After about 40 miles of nice moderate riding, I checked the right plug. It looked pretty good. And the bike was running fine at cruising speed. At low rpm though, it still isn't right and when I got back to the house the plug was getting black and fuzzy again from just a little bit of riding in traffic. Gas mileage was an all-time low at about 32mpg.
I would suspect that there is a problem in the carb body where the jet screws in except that it was fine until recently. This is perplexing. I guess I just need to order new jets, needles, etc. and start from scratch.
Oh, when I put new plug wires on, I cleaned up all the coil connectors and swapped the coils side to side. Problem stayed with the right cylinder. I need a spare R bike to swap parts on!
Thanks for all the help.
Cheers!
Craig
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Old 11-20-2010, 03:31 PM   #17
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In all of the disassembling/assembling of the carbs, have you checked to see that you haven't bent the needle?
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Old 11-20-2010, 03:40 PM   #18
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Quote:
Originally Posted by Craig in Alabama
(15mm or so)

It's still idles highest with the mixture screw all the way in (right cylinder only).
From Bing:
"If a too rich jet is selected, OR if the carb passages are partially blocked, these conditions will be indicated by the requirement of excessive screw setting in the CW direction."


15mm of fuel in the bowl?

Snowbum suggests 24 mm. Although that doesn't seem like it that would require turning the idle mix screw all the way in.

From Snowbum:
http://bmwmotorcycletech.info/bingcv-2.htm

"Actual bowl fuel level: You can turn the gas off again, replace the bowl, turn gas on, allow bowl to fill, turn gas off, remove bowl quickly. Measure the fuel depth from the center bottom to the fuel top, using something small...such as the tip end of a vernier caliper, or a thin, narrow, machinists steel rule.
Do your best to have the bowl sitting flat and level on its base, and estimate the best you can with #1 eyeball, as there are meniscus errors, the exact height of the fuel from the bottom.
For the 32 mm carburetors, use 24 mm fuel height.
For the 40 mm carburetors, use 28 mm fuel height.
"

A clogged passageway?
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Old 11-20-2010, 04:33 PM   #19
Bill Harris
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Good. You've eliminated a lot of what the problem is not.

From your check of things and your test ride, it is clear that the problem is in the idle/low speed circuit. You are getting too much fuel metered to the air at that speed, which suggests too large an idle jet, a bad o-ring (which allows too much fuel to leak around the jet or a blocked idle air bleed (jet/drilling or passageway). An air bleed that is blocked will not allow enough air to "bleed" into the idle/low speed circuit. The effect is that the mixture becomes richer and richer at part-throttle as the speed increases up to the transition to the main (high-speed) circuit.

I used to have some good books on carbs from Solex and Weber which explained "how they does it" pretty well. I've not been able to find (yet) a great online explanation. Yet.

Here is a pretty good explanation, though:

http://www.chevyhiperformance.com/te...ics/index.html

And Wikipedia has a good general overview:

http://en.wikipedia.org/wiki/Carburetor

I'll keep looking.

Meanwhile, remove the idle jet and blow out the idle air passage with compressed air.... :)
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Old 11-21-2010, 07:22 AM   #20
Craig in Alabama OP
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More great info!
I don't think the needle is bent. But it's about to be replaced anyway.

"If a too rich jet is selected, OR if the carb passages are partially blocked, these conditions will be indicated by the requirement of excessive screw setting in the CW direction."
This sounds exactly like the condition I have. Where exactly do I look to clean out the idle air passageway?

I reckon I'll go take that carb off again and see if I can find any blocked passages. I thought I cleaned them up pretty good, but there are a lot of nooks and crannys in there.

Thanks for the links, Bill! Good reading.

Back to the garage! If I can't find anything today, I'm ordering new jets and needles and float nedles tomorrow.
Cheers!
Craig
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Old 11-21-2010, 07:25 AM   #21
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If you can, blow water or something thru the passages then you can see they are flowing and which one comes out where. I think there are two that open in the carb throat.
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Old 11-21-2010, 07:40 AM   #22
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Originally Posted by rufusswan
If you can, blow water or something thru the passages then you can see they are flowing and which one comes out where. I think there are two that open in the carb throat.
I use a can of carb cleaner and a red straw to blow through passage ways.
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Old 11-21-2010, 10:24 AM   #23
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Eureka!

Hi Folks,
I figured out which air passage fed the idle jet and verified that it was clear. But I noticed that the space the jet screws into wasn't nice and symetrical like the main jet area. It looks a bit irregular. I also noticed that when I screwed the jet in or out there wasn't much resistance from the o-ring like there should be. Hmmm...
Turns out that gas was apparently getting sucked up around the idle jet instead of just into the jet hole. I had a pack of o-rings that are designed to be used in fuel, so I got a slightly fatter one and doubled them up. Nice and tight when I screwed the jet in. Cautiously optimistic, I set the carb up like it should be (air screw 1.25 turns out) and put it all back together. I knew it was going to be right when I had to use the choke to start it up. Then it went into a nice steady idle with the air screws where they are supposed to be.
I took it for a warm-up ride and everything feels just like it should. Transition off idle is much smoother. I balanced the carbs when I got home and it was much easier than it has been before. I'm going to take it for a ride in a few minutes and verify that everything is right. Hopefully my mileage will be a lot better.
So I don't know if I put the wrong o-ring on there when I originally cleaned out the carbs or if the idle jet orifice is buggered up, but it seems to be fixed. I really appreciate everyone's input.
I'll report back after the ride.
Cheers!
Craig
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Old 11-21-2010, 11:47 AM   #24
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Good. You're making progress one little chip at at time.
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Old 11-21-2010, 11:59 AM   #25
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If the right side carb has ever been blocked and clogged and if a PO has ever used a piece of wire or a small drill bit to clean the main jet, this will be the problem, I know, it's happened to me on a carb before, I chased the rich condition through every avenue till I got a new main jet and eye-balled the 2 jets side by side, the "used" one was significantly bigger. Put the new, correct-size jet in, problem solved instantly.
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Old 11-21-2010, 12:13 PM   #26
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Quote:
Originally Posted by Craig in Alabama
Hi Folks,
But I noticed that the space the jet screws into wasn't nice and symetrical like the main jet area. It looks a bit irregular. I also noticed that when I screwed the jet in or out there wasn't much resistance from the o-ring like there should be.
I'm curious about the irregularity of the carb body. Is it oval as if it was clamped in a vise? The threads buggered? Not a big deal, just curious.
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Old 11-21-2010, 12:48 PM   #27
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Soft brass threading into softer pot metal. Get heavy-handed and anything can happen.
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Old 11-21-2010, 01:25 PM   #28
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I skimmed through the posts and I hope I am not repeating this. But is it possible that the enrichener is in backwards? I was having trouble with cold starts when I got my airhead. And when it was warm one cylinder was way rich with black soot on the plug. I was reading that the enrichener is easy to put in backwards. I tore into the carb and sure enough mine was backwards. I turned it around and it starts no matter how cold and runs like a champ.
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Old 11-21-2010, 01:38 PM   #29
Craig in Alabama OP
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Ta da!

I just got back from a test ride. The bike ran great! I left with a full tank and put 95 miles on of mostly back roads at 60 - 70 mph. I used 2.25 gallons of fuel which puts my mileage at about 42mpg! And did I mention the bike ran great?

Granted I probably need to do some fine tuning to the carbsync, but this is certainly something I can live with. I balanced the carbs to be smoothest at about 3k rpm. Idle was fine and I think everything is hunky dory. I haven't pulled a plug yet, but I'm sure it will look better than yesterday (same route - 30mpg).

The opening where the idle jet goes looks like someone either screwed the wrong thing in there or cleaned it out with a screwdriver. I don't know. The other openings are nice smooth bores with nice clean threads. This just looks messed up, but the jet screws in just fine and the threads don't appear to be messed up. Next time I have to take the carbs off (which I hope is a while), I'll compare. But for now, I'm going to leave it alone.

Maybe I used the wrong o-ring initially, but I was very careful (I thought). In any case, all seems to be good for now.
Thanks, everybody!
Craig
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Old 11-21-2010, 06:13 PM   #30
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If that idle jet carb passage is damaged, Bing has a "carb doctor" who can reportedly work miracles on the damaged threads/jet seat/etc. If that looks like it will be a problem, you might want to give Bing a call and see if they can do anything with it.
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