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2002 Honda shadow 750 ACE bobber
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I have my ‘02 750 ACE and the front cylinder sounds strange and is sucking in from the exhaust where the rear cylinder is just blowing out exhaust. I’d imagine this is due to my exhaust valve not closing all the way on the front cylinder. Carbs are also fully in sync but the front cylinder is not running the same and I’d imagine this would be my problem. Any suggestions before I tackle this? also any tips on valve adjustment would be appreciated. Not sure what the spec is on these motors
 

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1999 Shadow 750 ACE VT750CD3 Modified
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4,969 Posts
You can't effectively sync carbs if you have valve clearance problems.
Task #19 in the Attached manual. (Thanks to "PlaneCrazy")
For the Factory Service Manual take a look in the "stickies" in this forum listing.
It is a tedious job, but not particularly difficult if you have the tools.
 

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3,278 Posts
I'd run some combustion chamber cleaner through 1st, if it's carbon build-up holding a valve open, any adjustment may not be accurate... Seafoam DeepCreep or Amsoil PowerFoam are a couple, there are others.
 
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1983 Honda vt750 Shadow
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20,337 Posts
We used to hold a dollar bill against the end of the exhust pipe on older cars to see it if got sucked back agaist the pipe as the engine idles. Especially if it had a misfire. A burned valve would suck back, a bad spark plug woldn't do that.
 
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Ah, separate pipes. I vaguely remember hearing about that method decades ago, Had completely forgotten it (along with who knows how much else I've forgotten...)

On another note, checked the valve clearances on my 03 750 Ace a couple weeks ago while I had the carbs off.. Every single one was in spec. 16K miles. they were close to minimums, but still in spec, left them alone.
 

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2013 Honda Shadow Phantom 750
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4,801 Posts
You may well have a valve problem but it is not valve lash adjustment. When the end of the valve and the rocker arm wear they get more space between them. That means that the valve will open later and close sooner than it would with the proper clearance. We are only talking about a few thousandths of an inch here so I doubt it would be “sucking”.

From what you have described I would say a burnt valve or seat. You need to do a proper compression test for starters.


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