Backfire on decel-carb
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5th Gear
Joined: Apr 2006
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Backfire on decel-carb
Hi,
I need some help. I am still new to diag Harley problems. I have gone through the forum and tried some of what I saw. My wifes trike is an 87 Softail with and S&S carb. I have new plugs, wires and coil.
The problem is when shedecels at higher speeds (like 65 to 70mph) it will backfire flame out the exhaust and the bike will go completly "dead" for a second, then come back like nothing happened. It doen't always do it. Seems like once it starts, it happens more often. After changing the coil, it seemed to take a lot longer before it backfired. We thought for a few that the coil fixed it, and of course after she gave me the thumbs up that it was okay, it backfired...go figure...
Any help on this would be greatly appericiated!
Nick and Sue
I need some help. I am still new to diag Harley problems. I have gone through the forum and tried some of what I saw. My wifes trike is an 87 Softail with and S&S carb. I have new plugs, wires and coil.
The problem is when shedecels at higher speeds (like 65 to 70mph) it will backfire flame out the exhaust and the bike will go completly "dead" for a second, then come back like nothing happened. It doen't always do it. Seems like once it starts, it happens more often. After changing the coil, it seemed to take a lot longer before it backfired. We thought for a few that the coil fixed it, and of course after she gave me the thumbs up that it was okay, it backfired...go figure...
Any help on this would be greatly appericiated!
Nick and Sue
Tourer
Joined: Jan 2007
Posts: 331
Likes: 0
From: Heppner, Oregon
RE: Backfire on decel-carb
Have you done any engine mods or did this just start happening? Have you checked the engine timing? Does the S&S have high speed jets and if so could it be running lean at high rpms? just thoughts.
Road Warrior
Joined: Jul 2006
Posts: 1,532
Likes: 7
From: Rochester N.Y.
RE: Backfire on decel-carb
By your description , the engine dies for a second then backfires a flame out the pipes.
This would make sense if you lose ignition for a split second and regain it again.
At the speed she's going , you will have delivered some fuel which wasn't ignited , then when you regain ignition , it burns the raw fuel
that has accumulated in the pipes , then BANG.
Sounds like the ignition problem is still there....
You could tape a voltmeter to the bars and watch for a voltage dropout to the ignition coil at that speed on decell..
Maybe you have a wiring problem to the ignition coil at that vibration frequency.
The wiring may be just chafed slightly and grounds or shorts just then.
If you had a jetting problem , it should be more consistent at that speed , gear , and decell.
When I was a kid driving stick shift cars , we would shut off the ignition going down hill and when you turn it on again , we got a big bang for laughs.
Sounds just like what you have.
Mick
This would make sense if you lose ignition for a split second and regain it again.
At the speed she's going , you will have delivered some fuel which wasn't ignited , then when you regain ignition , it burns the raw fuel
that has accumulated in the pipes , then BANG.
Sounds like the ignition problem is still there....
You could tape a voltmeter to the bars and watch for a voltage dropout to the ignition coil at that speed on decell..
Maybe you have a wiring problem to the ignition coil at that vibration frequency.
The wiring may be just chafed slightly and grounds or shorts just then.
If you had a jetting problem , it should be more consistent at that speed , gear , and decell.
When I was a kid driving stick shift cars , we would shut off the ignition going down hill and when you turn it on again , we got a big bang for laughs.
Sounds just like what you have.
Mick
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