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Quick Questions on VM Carbs (Keith Krause, you da expert?)

  • Thread starter Thread starter bgk
  • Start date Start date
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bgk

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On my VM carbs, #1 has no vent outlet nipple(a blank plug where a vent outlet nipple looks like it should be), #2 and #4 have vent outlet nipples which were originaly connected to vent hoses, which I have removed at Keith Krause's advice because I'm running a 4 into 1 exhaust pipe and 4 individual K&N filter pods, and #3 nipple is hooked to a hose to the petcock to open the fuel flow with vacuum.

Here are the questions:

Do I have uneven vaccuum of fuel flow from each carburetor bowl in comparison between one carb to another?

If so, how do I adjust for this?

Why is carb #1 blanked off, if carbs #2 and #4 are vented?

Anything else I need to know about this?
 
If you look at the carbs there is a small rubber hose by the #2 carb vent this connects the two carb vents together same with 3&4
 
Thank you SDL. I have been aware of the hose connections between Carbs 1 and 2, and 3 and 4, but I'm still wondering if there is uneven vacuum in comparison among all the carbs, particularly as Carb 3 has to "pull" the petcock open, whereas Carb 4 vents direct to atmosphere, Even though there is a crossover hose between Carbs 3 and 4, I assume the vacuum "takes the path of least resistance" so there would be an uneven "pull" between these two carbs. I'm probably worried needlessly, but I figured if anybody anywhere knew the answer, it would be here on the GSR.

The reason that supports my concern is that Carb #3 always seems to run a little richer after carb bank removal, inspection, cleaning, etc. and then reinstallation on bike. After I install the carbs on the bike, I "static tune" the carbs by adjusting the low speed fuel and air screws with the engine idling in the garage. I adjust the carbs "by ear and by feel" for best idle and best response for a quick "whack open the throttle" test. Then I take a test ride and then inspect the spark plugs. #3 carb is always a little richer, whereas I would expect it to be a little leaner because some of the vacuum has to pull the petcock open.

If these questions sound ignorant, please understand that I am a rookie mechanic, who has reached the stage of "having just enough knowledge to be dangerous"!
 
If #3 is richer than the others and that carb is clean, in good mechanical condition,(no serious needle jet/jet needle/o-ring wear) and the float level is correct, then I think you may have a leaking petcock diaphragm or the slide is slightly lower than the others when you do your manual synch'.
A lower slide will raise the vacuum and richen the mixture. These carbs need to be set with a vacuum tool.
The floatbowl vents are only vents, they are not designed to have an effect on vacuum. Each vent serves 2 carbs, everything is "even".
With the increased air intake when adding pod filters, the bowls ability to vent is inadequate. We cannot increase the venting, we can only minimize the resistance. That's why the tubes must be removed or you will experience fuel starvation. If the tubes are left on, a vortex is created and this has a negative effect on venting. If you increase the ability of the jets to draw fuel, you must also "increase" the bowls ability to vent.
 
Keith,

I never thought of a petcock leak. Now that you mention it, I recall that I often notice a faint smell of gasoline when I go into the basement garage to start or work on my bike, or just to get something from the garage. (I'm a lucky guy, I have two separate garages. The basement garage is mine, all mine!)

I've just always figured that a 25-year old bike always has a little gas and/or oil smell. Plus, that garage houses all my small-engine internal combustion stuff: lawnmowers, weedwacker, leafblower, chain saws, etc. All that stuff smells like gas.

I'll check the petcock when I get the time and motivation.

Thanks for your insight. (You are da expert!)
 
bgk, thanks for the "expert" compliment, but "trial and error king" is more like it! :lol:
 
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