1981 cb650c carb cleaning and other issues

If it's broken or just needs tweaked

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ballinchestr
Posts: 1
Joined: Thu Aug 02, 2018 9:21 pm

1981 cb650c carb cleaning and other issues

Postby ballinchestr » Wed Aug 15, 2018 2:21 pm

First post here, so go easy :)

I bought a 1981 cb650 custom last month. I bought it with an existing idle problem, in which it will immediately die when the throttle is let off. Other than that, it runs well while riding at speed. I pulled the carbs and checked out the jets. I did some searching on here, and found out that mine has the PITA pressed and recessed jets. I have some pictures I can post later tonight. The idle jets are completely clogged. I followed the carb manual's advice and picked up some high E guitar string, but it wouldn't unclog them, whatever's in there won't budge. What would be the best way to clean them out? I've read up using the forum, some tap the jets and pull them out, some people dunk the whole thing in an ultrasonic. Anyone have a recommendation for the easiest way to get these clear?

My other concern is that the engine is running lean because of this. I pulled a plug and it looked a little dry but not too bad. I'll pull them all once I ride home today and post a picture. I'm just concerned that it's running lean while slowing down after a downshift, because when I let on the throttle again to speed back up, it sometimes jerks forward, and if I give it gas slowly it backfires a little bit. Tell me what you think, and I'll be posting some pics asap.

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Volker_P
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Location: southern Germany

Re: 1981 cb650c carb cleaning and other issues

Postby Volker_P » Thu Aug 16, 2018 3:42 am

Welcome here! :D

ballinchestr wrote:... My other concern is that the engine is running lean because of this. I pulled a plug and it looked a little dry but not too bad.
...


CB 650 plugs typically look a bit lean. A bit of white is still all right at least for highway riding.
The idle system won't really affect mixture at load, rather airbox, jets, and floater level are responsible here.
Throttle response at load changes may however be affected, so fix your idle system and have a look for possible cracks at the "T-vents" between the carbs.
Cosky's great (free) online manual: http://cosky0.tripod.com

forum links to common technical issues


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