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1983 Honda vt750 Shadow
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Discussion Starter · #1 ·
I have had a 1983 750 shadow for only a few months and it runs well, no miss fire.
On deceleration especially down a grade, it pops out the exhaust all the way down to stopping.
I have after market twin exhaust, so it doesn't have the crossover chamber the original exhaust had.
I wonder if some of you have changed exhaust from the original and had some of this decel. popping also.
OR is it another situation???
I have read that too lean idle mixture can add to this. I tried richening up the mixture screws but it didn't change.
In my mind adding more fuel on decel. would actually cause more exhaust pop. ( Cars used to have an anti-backfire valve to stop this problem.)
Any ideas and fixes?
 

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Is your aftermarket exhaust maybe not sealed at the cylinders?
 

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Later model shadows do have the air cut-off so popping isn't usually a problem. Not sure if that applies to '83. Smilie asks a good question about if its coming out of the pipes or if the pipes aren't sealed all the way.

Popping CAN come from too lean a condition, so don't rule it out. If too lean (especially knowing you have aftermarket exhaust) this should be fixed. Lots of info online about re-jetting, depending on how much you want to tear into it.

NICE looking bike. Hope you get this solved.
 

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1983 Honda vt750 Shadow
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Discussion Starter · #4 ·
Thanks for the reply. I had the pipes off at the heads and the gaskets looked good but it is worth a recheck. The headers are still factory but the mufflers are aftermarket.
I don't have the air valves on this early engine.
 

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If you reused the old gaskets they will leak and cause popping ( ask me how I know). They are cheap 2.50 a piece or less just replace them. If you ever remove the pipes just plan on New crush gaskets every time.
 

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I have read in these forums that one can only go so far with the idle mix screw. If it does not cure the issue, re-jetting is the fix. After replacing the crush gaskets, of course.

Mine has stock pipes, and still pops a little. Since it runs so well, I have resisted buying new jets but at 25 years of age (the bike that is), I am probably looking at a carb overhaul at some point. Will wait until the performance deteriorates.
 

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1983 Honda vt750 Shadow
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Discussion Starter · #8 ·
Thanks for the info. and I will re-gasket those headers.
 

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i looked at an 83 750 parts fische. I didn't see any cut off valve on your carbs. I was thinking that's what it was. on my 85 I've got one, that's what its for is to stop popping on decel.
 

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I cannot endorse that practice [of putting new gaskets on top of old gaskets], as the build up of old gaskets will eventually cause air seepage. They aren't that hard to pick out.
Perhaps layering 4 gaskets on top of each other, as I do, lost count, isn't proper, but then a 2-gasket layer is okay or reasonable. This is especially true for aftermarket pipes as the 2 header bolts are tricky to tighten down evenly because the lackey flange on the aftermarket pipes bends unevenly when screwing in the header bolts 180° opposed to each other, torque readings aside.

That is, after loosening the opposite bolt to correct any uneven-ness you'd left with a gap on the smashed ring gasket at that quadrant since the gasket, a hollow copper ring, doesn't expand back to shape when pressure is eased up on it. What I mean is that having a thicker gasket layer at your disposal gives you more meat to work with. Also, if the pipes have to be removed for whatever reasons, a thicker layer may save buying new gaskets to re-seal up the same joint.
 

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I bought my 05 Spirit 1100 last June with very low mileage--8600 kms--from a much older gentleman who babied the heck out of this bike. I put another 15, 500 kms on the bike before I stored it for the winter and it's always made a cool sputtering sound on decal. I just thought this was the nature of the bike. No loud popping sounds noted and I'm very familiar with bangs and pops on decal and shut-off as these are very well known for my other bike, an S40 Suzuki. Is my sputtering notes on decal on my Honda abnormal then? Input and advice is appreciated. I never gave it a second thought until reading through this thread.
 

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I bought my 05 Spirit 1100 last June with very low mileage--8600 kms--from a much older gentleman who babied the heck out of this bike. I put another 15, 500 kms on the bike before I stored it for the winter and it's always made a cool sputtering sound on decal. I just thought this was the nature of the bike. No loud popping sounds noted and I'm very familiar with bangs and pops on decal and shut-off as these are very well known for my other bike, an S40 Suzuki. Is my sputtering notes on decal on my Honda abnormal then? Input and advice is appreciated. I never gave it a second thought until reading through this thread.
No one had to chance to help me out by responding to my question here, so I thought I'd better respond to my own post to bump this thread back up into member consideration terrain...any knowledgeable responses will be appreciated.
 

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You need to make a video of this in order to answer it. One mans sputter is another mans normal decel noise.
 

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No one had to chance to help me out by responding to my question here, so I thought I'd better respond to my own post to bump this thread back up into member consideration terrain...any knowledgeable responses will be appreciated.
Your carbs air/fuel settings might be in need of a slight adjustment. It's been brought up before on the forum but I can't recall which way you need to turn the A/F screws and if it's a lean or rich mix that causes this. Hopefully someone will add their thoughts to help!
 
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