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Discussion Starter · #1 ·
My bike sat for 2 years when I started it up it wouldn’t idle. I took the jets out and the idle jet was completely clogged. I cleaned everything and put it all back together. When I started it up it smoked quite a bit and ran rough. Coincidentally I removed the petcock vacuum line and it purred like a kitten until it ran out of fuel (10 secs). I repeated the test and it happened the same each time. It seems like it’s dumping too much fuel with the vac line attached. Am I missing something?
 

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1999 Shadow 750 ACE VT750CD3 Modified
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It could be several things, but my best guess is that the diaphragm in the petcock which acts as a valve is leaking.
I take it this is a 2004 or later Aero or 2007 or later Spirit. I really helps when we know the year and model name as well as the displacement.
Some people add it in their account details or signature so that it pops up on any of their postings with no further input.
BTW welcome to the forums.
 

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Discussion Starter · #3 ·
It could be several things, but my best guess is that the diaphragm in the petcock which acts as a valve is leaking.
I take it this is a 2004 or later Aero or 2007 or later Spirit. I really helps when we know the year and model name as well as the displacement.
Some people add it in their account details or signature so that it pops up on any of their postings with no further input.
BTW welcome to the forums.
Thanks for the input. This is a 2007 Aero 750. If the diaphragm is leaking would that dump too much fuel to the carb? Also shouldn’t the float control the fuel intake?
 

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1999 Shadow 750 ACE VT750CD3 Modified
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It is possible to suck fuel through the vacuum port, no carb involved.
 

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2001 Valkyrie I/S
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6,479 Posts
You can just order what they call a cover set for the petcock that includes that diaphragm
 
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Discussion Starter · #7 ·
Update: I replaced the petcock assembly and the problem is exactly as is was before. Next I bypassed the gas tank entirely and ran the bike from a small funnel of gas. It ran the same until almost all of the gas was gone, then it ran perfectly for the last 10 secs before running out of fuel. Now What? Float problem or float needle?
 

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2001 Valkyrie I/S
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Go through the carbs again, even the most experienced her often end up taking them off two or three times.
 

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Discussion Starter · #9 ·
A friend said I may have opened up the idle jet too much. I did use a drill bit manually to clean it out and got some brass chips out. I ordered a new one today.
 

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1983 Honda vt750 Shadow
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That is the school of hard knocks and we are all attending ! :rolleyes:

My pilot jets were #40 and I wanted to richen it up a little .
The smallest drill I had was a .020" and it went from about 16 thousandths up to 20 thousandths, which doesn't sound like a lot, but I lost 10 MPG so it was too much.
My idle screws are only out 1/2 turn now, when they were out 2-3 turns before.

So the old saying= "if some is good, too much is better"- doesn't always work with carbs.

Look at the color of your spark plugs they are your mixture feedback.
 

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'83 VT750C
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LOL! That’s what my father did to ‘clean out’ the jets on the bike I’m working on. The look on his face when I showed him the difference from his to a new set of slightly over-sized jets was priceless! The hole he‘d left was gigantic...
 

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'83 VT750C
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Yep, that looked like Dad’s handiwork. Though he said, “Fuel will still go through, won’t it?” To be fair, he couldn’t believe the hole was was small as it really is.
 

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My bike sat for 2 years when I started it up it wouldn’t idle. I took the jets out and the idle jet was completely clogged. I cleaned everything and put it all back together. When I started it up it smoked quite a bit and ran rough. Coincidentally I removed the petcock vacuum line and it purred like a kitten until it ran out of fuel (10 secs). I repeated the test and it happened the same each time. It seems like it’s dumping too much fuel with the vac line attached. Am I missing something?
Replace the petcock, the vacuum diaphram is bad and it is sucking fuel into the intake from that small vacuum tube, I had the exact same problem on mu 06 Shadow Aero VT750c, you can order a new petcock with the strainer already on it for about 20 bucks on Amazon. That little diaphram on the petcock keeps the fuel from flowing if the engine is not running and if it has a hole in it, it will suck fuel straight into the rear head, where it is connected to. Just reember to replace the strainer with the petcock, the old one will be somewhat difficult to get out, but it will come out of there, they are notorious for getting stuck in the threaded nipple that the petcock screws onto. Hope this helps !!
 
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