SCC - Won't Run Below 2000 RPM


Information and questions on GL1000 Goldwings (1975-1979)
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bbuice
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1975 GL1000

SCC - Won't Run Below 2000 RPM

Post by bbuice »



I know this is frowned upon by many but after spending $500+ a few times to get my 1975 GL1000 Carbs rebuilt I decided to try a single carb this year. I purchased a manifold and a 34PICT-3 carb. I followed the instructions and have it all installed. No matter what I do I can't get the bike to idle below 2000 rpm. I have looked through this forum and haven't seen anything much about this issue. I have Dyna ignition on the bike if that makes any difference. Can anyone offer any advice?

I just thought of another question. In my reading through other forums I came across a couple of posts regarding icing of the manifold. Is this a big problem and does it keep the bike from running? Does it happen when riding or just until the bike is warmed up?

Thanks.

Benny


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Benny Buice
Marietta, GA
1975 GL1000
2003 GL1800
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WingAdmin
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Re: SCC - Won't Run Below 2000 RPM

Post by WingAdmin »

Carburetor icing can affect any carbureted engine.

When incoming air is rushed through the carburetor venturi, it accelerates in order to squeeze through the narrow opening. As it accelerates, the pressure drops, which is what is then used to suck fuel out from the jets.

As the pressure drops, the temperature also drops. The faster the air is accelerated, the more the temperature drops. If there is moisture in the air, and the temperature in the venturi drops below freezing, you can end up with ice collecting. This can happen when ambient temperature is as high as 70 degrees F.

Carburetors which flow more air (i.e. a single carb conversion) will suffer this more than smaller carbs.

It's a significant problem on small aircraft, where carb ice can cause engine failure. For this reason, small airplanes have a method of directing heated air into the carburetor intake, to keep the temperature above freezing. Motorcycles will not have that ability. Some will only have the problem if the engine is cold (engine heat offsets it), but some can get it at lower temperatures regardless of engine temperature.
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bbuice
Posts: 11
Joined: Sat Mar 13, 2010 9:24 am
Location: Marietta, GA
Motorcycle: 2003 GL1800
1975 GL1000

Re: SCC - Won't Run Below 2000 RPM

Post by bbuice »

Thanks for that explanation. Sounds like it works sort of like refrigeration.
-----------------------------------------------------------
Benny Buice
Marietta, GA
1975 GL1000
2003 GL1800
User avatar
WingAdmin
Site Admin
Posts: 22423
Joined: Fri Oct 03, 2008 4:16 pm
Location: Strongsville, OH
Motorcycle: 2000 GL1500 SE
1982 GL1100A Aspencade (sold)
1989 PC800 (sold)
1998 XV250 Virago (sold)
2012 Suzuki Burgman 400 (wife's!)
2007 Aspen Sentry Trailer
Contact:

Re: SCC - Won't Run Below 2000 RPM

Post by WingAdmin »

bbuice wrote: Mon Jul 20, 2020 7:18 pm Thanks for that explanation. Sounds like it works sort of like refrigeration.
Same physics in play. Drop in pressure means absorbing heat (getting colder). Increase in pressure means giving off heat.
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Bzrut
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Re: SCC - Won't Run Below 2000 RPM

Post by Bzrut »

So, is there any solution to this problem thanks.
Just get out n ride
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Rambozo
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Re: SCC - Won't Run Below 2000 RPM

Post by Rambozo »

Bzrut wrote: Sat Jul 17, 2021 9:32 pm So, is there any solution to this problem thanks.
Carb heat. Either by exhaust heat, coolant heat (air or water), or electric heat.


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