85 Aspancade- Pops back thru carbs


Information and questions on GL1200 Goldwings (1984-1987)
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CTInspect
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Motorcycle: 1985 GL1200A Aspencade

85 Aspancade- Pops back thru carbs

Postby CTInspect » Sun Mar 21, 2010 5:48 pm



85 Asp. starts great, idles fine and runs pretty nice. There is a pop back thru the air plenum right between about 1900 and 2000 rpm. Below that is ok and above runs like a charm. I pulled the carbs just for a check and they are pretty clean. I find or see nothing odd, vac lines look good, cut off appears to be ok, no noted damage. Thats what I thought it might be. Ive ordered rebuild kits, gaskets, cut off and slides anyway even though they all look ok.
Im figuring it should be in the air/fuel portion, ie carbs and so on and not an engine issue since its only at a specific range of rpm.
Any ideas out there on what else I should be looking closer at?



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tricky
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Re: 85 Aspancade- Pops back thru carbs

Postby tricky » Sun Mar 21, 2010 6:08 pm

Possibly Faulty slow air cutoff valve.... just a guess
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WingAdmin
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Re: 85 Aspancade- Pops back thru carbs

Postby WingAdmin » Sun Mar 21, 2010 10:21 pm

Is it a pop right at that RPM, or when the engine decelerates through that speed?

CTInspect
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Re: 85 Aspancade- Pops back thru carbs

Postby CTInspect » Mon Mar 22, 2010 4:46 am

Its on acceleration and always in the same rpm range, I dont recall anything on decelerating. Sometimes alittle choke helps.

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Re: 85 Aspancade- Pops back thru carbs

Postby WingAdmin » Mon Mar 22, 2010 6:55 am

This can be the symptom of a few different things:

- Timing off
- plug wires mismatched
- intake valve not closing completely (debris in valve/damaged valve)
- lean fuel condition

If you take the air filter off and run it without an air filter installed, does it get worse? Does it get worse when it's colder out? If so, then you've got a lean fuel condition in whichever carb is causing the problem. If you have an infrared thermometer, you can point it at the exhaust pipes coming out of the bottom of the cylinders - whichever one is the hottest one is the one that is running lean.

CTInspect
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Motorcycle: 1985 GL1200A Aspencade

Re: 85 Aspancade- Pops back thru carbs

Postby CTInspect » Mon Mar 22, 2010 2:11 pm

- Timing off
- plug wires mismatched
- intake valve not closing completely (debris in valve/damaged valve)
- lean fuel condition
Well the carbs are off of it now and waiting for the kits. Prior to this there was a bent Exh valve that was done. (So Im pretty sure the rest on that side were good) I triple checked the timing when it was done and since it starts on a dime, click, start .... cam notches both @ marks, engine @ T1.
I will visually check the Int valves with lights, and the wires(new wires, caps, plugs) while I wait for parts.
But Im not sure why @ 2000rpm only??, most of the above seems to me that they would be an issue at almost any rpm. This starts really good, fairly smooth to 1900/2000, pops, then like a jet after that?
But it will give something to do ...
By the way, the Inf therm is how I found the exh valve.

CTInspect
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Re: 85 Aspancade- Pops back thru carbs

Postby CTInspect » Mon Mar 22, 2010 6:40 pm

? Firing order ? They say 1324, but if you look at it the way you would a car and go in order ( ie first wire, 2nd and so on) then it should be 1234. I tried an attachment with this, hopefully it works. Thats the way mine is hooked up so I hope its right. Actually, if it was wrong Id be happy too, then I might have the Pop Back issue solved.
I pulled the plugs and they all look the same, hint of tan and clean so Im steering a bit away from lean on one, unless they all are. And have to wait to get a helping hand to check the valves, rather do it slow by turning the rear than cranking the engine.
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Re: 85 Aspancade- Pops back thru carbs

Postby WingAdmin » Mon Mar 22, 2010 8:57 pm

The diagram is correct. It fires the right coil, then the left, then the right, then the left. On the first firing, plugs 1 & 2 spark, but only cylinder 1 has fuel, so it ignites. The next firing, plugs 3 & 4 spark, but only cylinder 3 has fuel, so it ignites. The next firing, plugs 1 & 2 fire again, but only cylinder 2 has fuel, so it ignites. The last firing, plugs 3 & 4 spark again, but only cylinder 4 has fuel, so it ignites. It uses "wasted spark" to spark a cylinder that is in the middle of exhausting - which means only two coils are needed instead of four. The end result is that the sequence shown is correct, 1, 3, 2, 4.




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