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MarkT Exhaust
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Author Topic: Left side backfire.  (Read 977 times)
fiddle mike
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Nothing exceeds like excess.

Corpus Christi, TX


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« on: January 20, 2016, 12:04:26 PM »

My '97 fires up, and runs good, for a while.  After a few miles, she begins running rough and backfiring on the left side.  After she sits for a few minutes, she fires up and rev's OK.
.
I've set the valves, balanced the carbs, charged the air filter, run a bunch of B-12 through, and tried running with the fuel cap open.
The bike has over 200K on the clock, so I'm thinking, maybe, the problem is a coil.
I could used some input.
TIA
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indybobm
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Franklin, Indiana VRCC # 5258


« Reply #1 on: January 20, 2016, 01:00:35 PM »

Are all 6 enriched valves disengaging properly when you push the choke knob up?
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VRCC # 5258
fiddle mike
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Corpus Christi, TX


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« Reply #2 on: January 20, 2016, 01:09:01 PM »

I haven't looked.  Thanks for the tip.
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Steel cowboy
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Spring Hill, Fl.


« Reply #3 on: January 20, 2016, 02:35:49 PM »

Can you swap the coils and see if Another side does it
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fiddle mike
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Corpus Christi, TX


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« Reply #4 on: January 20, 2016, 03:01:04 PM »

Can you swap the coils and see if Another side does it

That shouldn't be a problem, but I just looked at the fiche, and  the left coil also fires a right-side cyl.
I mean to check out the grounds and connections whenever I can get the tank off.
I guess I need to run it till the problem begins, and see if I can isolate the misfire.

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97BLKVALK
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VRCC#26021

Detroit Lakes, MN


« Reply #5 on: January 20, 2016, 03:01:19 PM »

Congrats on 200K cooldude

Have you looked at the 12 clamps on your intake and possibly your 6 exhaust manifold nuts.

Good Luck

Michael


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Skinhead
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J. A. B. O. A.

Troy, MI


« Reply #6 on: January 20, 2016, 03:16:04 PM »

Vacuum Leak?  Hoses and Orings?
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Troy, MI
DK
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Little Rock


« Reply #7 on: January 20, 2016, 04:21:34 PM »

Take either a propane torch or an aerosol can of starting fluid & spray around the intakes and various vacuum connections while watching for a sudden increase of idle speed.

Dan
« Last Edit: January 20, 2016, 05:33:17 PM by DK » Logged

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Patrick
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VRCC 4474

Largo Florida


« Reply #8 on: January 21, 2016, 06:13:04 AM »

Just to check, the left side is the shifter side. Is the bike sitting upright [ or almost upright] when is starts misfiring or is sitting on the side stand ?

It sounds like a lean condition, so spraying some ether [ start fluid] or using some propane around the carb and intakes bases is a good idea.

Have you tried sitting the bike upright and flushing fuel thru the carburetors ?  Open the drains and let the fuel flow for awhile.

See if you figure out if one cylinder is the culprit or there are more than one giving problems.

It doesn't sound to me like an ignition issue. You already know these use a waste spark system. But, it could possibly be a bad sparkler and examining/cleaning and swapping should figure that issue out.
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chris1998
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« Reply #9 on: February 20, 2016, 12:05:17 PM »

Try this first... The fuel petcock is activated by vacuum. So it closes automatically when you turn engine off. You really don't need to shut off fuel when you park the bike. The vacuum supplied to the petcock comes from one of your left bank cylinder runners. I had a problem with my 2000 std. years ago. It was fowling the left rear plug because of a perforated petcock diaphragm (leaking into the cylinder when parked.) It was dark and the others were clean. Popping after heating up was the indicator. Also, check all vacuum plugs on the runners. And the color of your tail pipes. My left was always darker and smoked ever so slightly on start-up.

To diagnose, I changed the vacuum hose to the next cylinder and moved the misfire and fouling as well.

Solution: A new petcock. (I found a very small perforation upon disassembly.) They were on inter- galactic back order at the time due to high demand. So I had to modify my old one until it came in.)

I hope this helps.

PS. MPG increased. Smiley

Good luck,
Chris
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