1st Generation Specific (1979-1985) 1979-1985 Discussion including performance modifications and technical support sections

12A Carburetor Help

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Old 09-28-09, 06:17 PM
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IN 12A Carburetor Help

I recently rebuilt the carburetor on my GS and installed it. When I reinstalled the carb and started her up the idle was very high at 2,000 RPM. When I rev the engine it makes a sound like you are putting your foot on and off the gas. I set the idle speed, and idle mixture screws to the base settings and it doesn't help.

I don't know exactly what is wrong, I made sure all the jets were in the correct slots so I don't believe it is a problem with the jets(but very well could be). If anyone has a picture of the vacuum hoses connecting to the carb, I may have plugged some in wrong. Any help would be appreciated.
Old 09-29-09, 11:55 AM
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Anyone?
Old 09-29-09, 12:07 PM
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I've got pix for an '80, but an '85 will be considerably different.

Have you tried downloading the Factory Service Manual from the FAQ? It might help.
Old 09-29-09, 12:14 PM
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Yeah did the carb come with a choke? There are aftermarket carbs that don't (I'm saving up for one currently).
Also with the rotary, 2000 rpm is not a obscenley high idle. I prefer that mine idles at 1600 at the lowest.
Old 09-29-09, 12:14 PM
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Also the motor and components from the '80 and the '85 are virtually the same. It's both the 12a motor.
Old 09-29-09, 12:22 PM
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The idle should be set at around 850 rpms. A 2000 rpm idle is a problem for obvious reasons.

I would suggest that you speak with our resident Nikki carb expert, Sterling. His website has all sorts of information on these carbs, including writeups, troubleshooting procedures, and pretty much a library of information. www.sterlingmetalworks.com

If that doesn't get you the information you need, you can ask him questions on his carb forum. www.sterlingmetalworks.com/bymc

Hope this helps.


.
Old 09-29-09, 02:52 PM
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Originally Posted by MeCalledEvan
Also the motor and components from the '80 and the '85 are virtually the same. It's both the 12a motor.
'Virtually the same...' with the exception of nearly all the emissions control equipment, which is what 80% of the vacuum hoses surrounding the carburetor are for.

Which is what the OP is asking after.
Old 09-29-09, 09:02 PM
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Thanks guys, I'll check out Sterlings website.
Old 09-29-09, 09:08 PM
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you mixed one of the jets at the bottom of the float bowls i rebuilt mine a month ago same thing pulled my hair out that was it
Old 09-29-09, 09:48 PM
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It's more possible I misplaced a few of the vacuum hoses than jets, as I checked the jets over and over to make sure 100% they were correct.

My vacuum hoses are definitely in the wrong spots. While removing the hose from the shutter solenoid valve the plastic piece that you slip the hose over broke off inside the hose. I'm not sure I could glue it back together. Does anyone know where you could buy replacements?
Old 09-29-09, 10:04 PM
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sound similar? http://www.youtube.com/watch?v=qBw2s3RjsD8
Old 09-30-09, 12:29 AM
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Carbs are pretty complicated. Just cause it has similar symptoms does not mean his problem is exactly the same as yours was. There are many things that could cause a weird idle. Don't get me wrong, that could very well be it. And the advice of someone like you who has recently done the same and already did the troubleshooting is invaluable. But it could be a lot of things.

And yeah, sterling's tuning page will be super helpful.
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