Popping and Banging


Information and questions on GL1200 Goldwings (1984-1987)
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seasicksid
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Location: Essex, England, United Kingdom
Motorcycle: 1984 GL1200 Interstate
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Popping and Banging

Postby seasicksid » Fri Nov 15, 2013 3:33 pm



My Gold Wing had been stood for five or so years. I've changed every service part possible in preparation for its re comission. It starts up first touch of the button. Idles reasonably smooth, no shakes. The problem occurs when I rev it. It pops and bangs before picking up the revs. Hesitates and nearly cuts unless I take it slowly.
If I open the choke slightly it revs smoothly and quickly but still pops occasionally. I've put fresh petrol in of course, and a carb cleaner additive.
Anything I should try next to smooth out the revs?

Sid



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WingAdmin
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Re: Popping and Banging

Postby WingAdmin » Fri Nov 15, 2013 3:59 pm

Popping like you describe is normally caused by a mixture that is too lean.

Vacuum in the engine is caused as a result of the pistons sucking air in, and the throttle restricting that airflow. The result between the throttle and the engine is vacuum. The air rushes through a more constricted area, which briefly speeds it up. As the velocity of air increases, its pressure decreases (called the Bernoulli effect). This increases the vacuum. This vacuum is used to suck fuel up out of the carburetor float chambers and into the airstream.

When you rapidly open the throttle, the vacuum in the plenum suddenly drops - because the throttle has opened up. As a result, the amount of fuel being sucked up also suddenly drops. This means you have less fuel and more air - which means you have a lean condition. When the mixture gets TOO lean, it will refuse to burn inside the cylinder, and the cylinder "misses" - which is the stumbling you feel. That unburned fuel/air mixture is then funneled into the exhaust, where it mixes with hot exhaust from the other cylinders. This causes the oxygen mixture to change, and the unburned fuel suddenly lights off, causing a pop noise (explosion in your exhaust).

To get around this problem, we have something called an accelerator pump. This is a special pump that gives a quick squirt of gas directly into the throttle plenum anytime you open the throttle rapidly. This extra squirt of gas enrichens the mixture and prevents the lean missing and exhaust pops.

My suspicion is that you have a nonfunctional or a compromised accelerator pump/circuit.

The fact that you can turn the choke on and it helps the problem supports this. Turning the choke on chokes off the air, enrichening the mixture (more fuel, less air).

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seasicksid
Posts: 38
Joined: Tue Oct 08, 2013 5:11 pm
Location: Essex, England, United Kingdom
Motorcycle: 1984 GL1200 Interstate
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Re: Popping and Banging

Postby seasicksid » Sat Nov 16, 2013 5:38 am

Thanks. I'll investigate right now.


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