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Just looking for some input on this subject. Seems that when these beasties sit for more than a few days, it seems to take too much battery to finally get fuel to the carbs and the engine to start firing. Even with batteries topped up it seems to take forever to get the thumper popping. Otherwise after starting the engines run perfectly. Am I missing something or is it just the nature of these critters.
 

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Put your bike type an year in your signature line.





If you don't have a vacuum petcock it doesn't rely on vacuum to let fuel in. With that being said. Gas is crap. This new stuff is the problem. It's like all the good stuff evaporates off leaving something similar to water. When I let my bike sit for over a week I usually drain the carbs before starting.
 

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O.K. I'm dumb. What a signature line?




You see down at the bottom of my post there's a bunch of writing and crap. Bike type and other. That's a signature line.



It's in the profile section. Just type the bikes year and type in there and everyone will know.
 

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Do the vacuum petcocks have a prime setting? if they do, that might help you a lot.
 

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I don't think they do. Not exactly like a friendly push mower. Pump the prime a few times and it's good to go. The only way I think you can open the vacuum side is to disable it or manually activate it. Maybe hook up a syringe to create vacuum and open it but it would be easier to just disable the petcock.
 

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There are a lot of bikes that do have a prime setting on the vac petcocks... I wonder if any could be adapted to fit.
 

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On occasion, I have disconnected the vacuum tube that goes to the right carb and temporarily connected it to the intake of an air-bed pump for a minute or so, rocking the bike slightly. Gss flows and it starts up with minimal cranking. I have considered altering the petcock, but I like the safety factor it provides.
 

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Just looking for some input on this subject. Seems that when these beasties sit for more than a few days, it seems to take too much battery to finally get fuel to the carbs and the engine to start firing. Even with batteries topped up it seems to take forever to get the thumper popping. Otherwise after starting the engines run perfectly. Am I missing something or is it just the nature of these critters.


This doesn't really help you, but my bike starts pretty well even after sitting a while.  Lately the weather's been unpredictable, yesterday it was below 30 in the morning and this morning it was near 40, and last week it rained a few days.  Point being, cold, wet, sitting a week or starting daily my bikes pretty consistent in how it starts.  Could it be your battery is just a little old and feeble?
 

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This symptom will occur less with correctly cleaned carbs,serviced starter motor,good coils plugs and caps.



My present CX500 ride can be left for long periods and will start on the button if the petcock is left on.My other one that is off the road for now needs the carbs doing again and if left for a week when I usually give it a maintenance start up can take a bit to get going.



I just spray some WD40 or Carb Brake cleaner into the Air-filter inlets as I crank it.



HTH
 

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When I know I won't be riding for a week or more I empty the float bowls of the old gas - seems to start better then when I leave it in there.
 

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Thanks for the link relic! There is a lot of cool stuff in that link.
 

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'84 CX650E that is evolving into a GL500
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I don't see anything about the petcock there, though.

The petcocks used on these bikes were never intended to be rebuilt but we used to recommend drilling out the staked posts to disassemble the petcock and flipping the "wafer" (round seal with 4 holes with ribs around them) to get a bit more life out of it, then drilling & tapping the posts to accept screws for re-assembly (I think that's what Phantom was referring to). That was a temporary fix at best 15 or 20 years ago and I seriously doubt that any petcock "rebuilt" that way now would last very long at all (ancient rubber hardened by decades of contact with a strong solvent and all).
Unfortunately none of us was able to find a replacement wafer that fit properly and the ones that needed to be stretched to fit didn't last long either.
Fortunately there are affordable aftermarket replacements available.

Re Spring Brook's original question, I think most of those who posted here today have seen this before but I'll add it in case someone else finds this thread who hasn't:

The vacuum petcock has 2 valves, a manually controlled valve that works the same as a non-vacuum petcock, allowing you to select between ON, OFF and REServe and a vacuum valve that prevents fuel from entering the manual valve when the engine is not running.

The carbs on these bikes have a tendency for the fuel in the float bowls to evaporate and fast enough that if they are not used for a week or so the level can get low enough that there isn't enough for the engine to start. The problem is that the vacuum petcock doesn't let any fuel into the carbs unless the engine is turning fast enough to produce vacuum so you have to crank the starter long enough for the engine to supply enough vacuum to the petcock to open the valve for a long enough time for the float bowls to re-fill and it is pretty easy to run the battery down doing that.

You have a few options when that happens:
  • If it has been sitting for a few days and you expect that it will be hard to start, before you touch the Start Button, vigorously whack the throttle open several times to operate the accelerator pump and squirt raw fuel into the carb throats.
  • If it has been sitting for a week or more and whacking the throttle doesn't help there are 3 ways to fill the bowls:
1) Disconnect the fuel line from the petcock, connect a funnel and pour 90cc of fuel in directly.
2) Disconnect the vacuum line from the petcock (this is the small barb farthest from the petcock's main body), connect a short piece of clean tubing in its place and apply vacuum (with a vacuum pump or just suck with your mouth) for about 10-15 seconds.
3) Disconnect the drain/vent line from the petcock (this is the small barb between the vacuum line and the main body), connect a short piece of clean tubing in its place and blow gently into it for 15-20 seconds.

Of course, the whole problem can be eliminated by converting to a non-vacuum petcock.
 
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