Vt500c back firing - Honda Shadow Forums : Shadow Motorcycle Forum

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Old 01-30-2013, 01:55 AM   #1 (permalink)
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Default Vt500c back firing

So I have a 86 vt500c. Its back firing on one cylinder and seems like its not firing with full steam on that cylinder. And it was kinda weak. I took it apart just now to see what's up. I was going to change the spark plugs and when I grabbed the rear-most plug wire, I think it was loose! I don't think it was actually snapped onto the spark plug.

So I plugged it in and put everything back together, but haven't started it up yet. I'll do that tomorrow during the day.

My question is, would one plug not firing cause the back firing and the weakness?

How do you change that plug anyways?

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Old 01-30-2013, 09:38 AM   #2 (permalink)
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Default Re: Vt500c back firing

Ran it this morning. It runs a heck of a lot better, but still backfires upon decel. If I am gentle with the throttle, it's pretty nice and smooth, but if I'm at WOT, it's kinda jerky... like its not always firing on all cylinders. Its haulin', then it kinda bogs, then it takes off again, then it bogs...

I guess I should pull and replace all 4 plugs.

Is it possible to get the plugs out without removing the [I think] valvecover?

What else could it be? I searched and found so much stuff on what to do if the vt500 doesn't run right, but I don't know where to start! There's just so many little quirks to these bikes!

When its running right, the thing is a lot of fun and rides very nice! (I think it does look a little goofy with my knees almost touching the handlebars!)

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Old 01-30-2013, 09:52 AM   #3 (permalink)
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Does the bike have the airbox, stock filter, stock carb jetting, and stock pipes?

The two difficult plugs can be removed with an 18mm thin walled socket with the round edges on the top ground down, and a wobble extension. Or you can pay for the Honda plug removal tool.
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Old 01-30-2013, 10:51 AM   #4 (permalink)
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Default Re: Vt500c back firing

It has an air box. Not sure if the filter is stock or not. It looks to be in good shape and clean, its orangish red. Does not look as dark as k&n red. Not sure if jetting is stock or not, but I took the carbs apart and cleaned it all out to get it running. Exhaust is stock. One of the coils has junkyard paint pen writing on it - it must be a salvage part.

Maybe the thing just needs ridden hard for a while. Its been years since its really been run.

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Old 01-30-2013, 12:41 PM   #5 (permalink)
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Have a good inspection to make sure the carbs are completely seated in the intake boots, and that the airbox is securely fitted to the carb intakes. Air leaks can cause a lean mixture which may cause backfiring.

Also may want to pull off the intake boots and inspect them for cracks. If in doubt replace them.

A high flow air filter may also cause a leaner condition, but I wouldn't think enough to cause frequent backfiring.
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Old 01-30-2013, 10:04 PM   #6 (permalink)
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Default Re: Vt500c back firing

I wonder if shimming the needles with washers would work on this bike. I did it on my nighthawk and it's much more responsive.

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Old 01-30-2013, 10:28 PM   #7 (permalink)
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Slow down!!

Fix your issues than modify as you like.
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Old 01-30-2013, 10:43 PM   #8 (permalink)
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Default Re: Vt500c back firing

It can't be that big a problem, I think. Its right on the edge of wanting to run right and not... just gotta find that thing or two that's not "just right".

So since one of my spark plug wires wasn't plugged in, that spark plug's gotta be really fouled. Is it possible that its still not firing because of how fouled it is?

So the back firing is caused by a lean condition? Hmm... gotta find out why...

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Old 01-30-2013, 10:50 PM   #9 (permalink)
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Quote:
Originally Posted by ken99287 View Post
So since one of my spark plug wires wasn't plugged in, that spark plug's gotta be really fouled. Is it possible that its still not firing because of how fouled it is?

Not likely as you have another one in that cylinder as backup. So were your carbs properly seated?
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Old 01-30-2013, 11:30 PM   #10 (permalink)
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Default Re: Vt500c back firing

I'll check it right now. I was busy after work buying and installing a new dishwasher for my fiancée. I figure since I bought and installed it, I shouldn't need to do any dishes! Unfortunately, I don't think it works out that way...

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