Mafic's Nighthawk CB650sc Starting troubles

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mafic
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Mafic's Nighthawk CB650sc Starting troubles

Postby mafic » Sun Sep 17, 2017 3:22 pm

Having a similar issue here. Last summer the bike would fire right up and hold a steady idle, pulled it out of storage this season and now it will not stay running. If I lay on the throttle while starting I can keep it running for moment. I have good spark on cylinders 1 and 2, while 3 and 4 have a weaker spark. The plugs were pretty fouled up so I cleaned up each one hoping that would be my issue, no such luck.

I'm thinking it has to be fuel related because 3 and 4 fire up and after a few attempts they get pretty hot while 1 and 2 barely get warm. I poured a little fuel into cylinder 1 through the spark plug hole, replaced the plug, and it quickly started up strong but died again after a few seconds. 1 and 2 were noticeably warmer after that last attempt.

Do I need to take the carbs apart for a cleaning? I know they are getting fuel, been feeding fuel directly in through a funnel and hose and the bowls drain fuel.

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GeorgeSweety
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Re: 1982 Nighthawk CB650sc Starting troubles

Postby GeorgeSweety » Mon Sep 18, 2017 1:26 am

Hi mafic, did you dry store the bike, drain the bowls before storage? You may be getting fuel into your carbs but that doesn't mean it is getting into the engine. After you try to start the bike can you take the plugs out of 1 and 2 to see if they are wet with fuel? I can't really see it being an electrical problem at the moment, more inclined to think it is blocked idle jets. Let us know the result. BTW, where are you located?

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Folsoml
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Re: Mafic's Nighthawk CB650sc Starting troubles

Postby Folsoml » Mon Sep 18, 2017 5:25 am

Your carbs almost certainly need cleaning. The ethanol fuel has turned to syrup in your float bowls and has plugged things up. Take a look at the carb cleaning manual sticky in the technical discussion forum.

PS: I made your issue it's own thread. That way there is no confusion as to which person's issue is being addressed.
Have a problem with your CB650? Have a technical question? Click here!


My Current Bikes: 2005 HD FLHTCUI Electra Glide Ultra Classic, 2007 Yamaha Vino,

mafic
Posts: 2
Joined: Sat Sep 09, 2017 1:35 pm

Re: 1982 Nighthawk CB650sc Starting troubles

Postby mafic » Thu Sep 21, 2017 9:01 pm

GeorgeSweety wrote:Hi mafic, did you dry store the bike, drain the bowls before storage? You may be getting fuel into your carbs but that doesn't mean it is getting into the engine. After you try to start the bike can you take the plugs out of 1 and 2 to see if they are wet with fuel? I can't really see it being an electrical problem at the moment, more inclined to think it is blocked idle jets. Let us know the result. BTW, where are you located?


Sorry to come back to this a little late, I'm one of those hectically busy college students. I attend a state school in northern Utah. To answer the other question:

When I initially removed and cleaned up the plugs 1 and 2 were pretty dry, this was after a failed attempt at starting. Today I sprayed a little starter fluid in the air box and the bike started and held a good idle for a few seconds. At this point I'm pretty confident that Folsoml is correct and I need to clean those carbs. Now my biggest challenge is to find out when I will have time this semester to do that ha ha ha

Thanks for your input guys, I am sure I will be back to update this once I have chance to get to those carbs.


PS: all the pipes felt equally warm after starting on fluid a few times, this sounds like good news to me!

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GeorgeSweety
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Re: Mafic's Nighthawk CB650sc Starting troubles

Postby GeorgeSweety » Fri Sep 22, 2017 1:31 am

Hi Mafic, yes Folsoml is correct, a good carb cleaning is in order by the sounds of it. Make sure to remove your idle jets if they are the pressed in type or you will not solve your problem, do it right first time then hopefully you won't need to keep pulling the carbs.


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