Topic: Carb help for a 1980 CB650

[arncruz]

I bought this 1980 CB650 a week ago and had not started per previous owner.  I put fresh gas, and changed the oil, spark plugs, and filter.  I placed oil in the cylinders prior to starting.  Luckily the battery that was in the bike only needed a good charge and it was working again.  I cleaned the carbs out as the float pins were getting stuck.  Well today, I was able to get this bike started but the only way to keep it running was to keep the choke open.  I messed with the idle dial and that helped a little but it would die shortly after I let go of the throttle.  then after the engine would stop, I would have gas pouring out of carb #1.  I'm not a mechanic but I play one at home.  I was happy to get this beast started and it sounds pretty solid.  No rattling and purrs really well.  Throttle response is a little sluggish but it will get up there.  Any advice would be appreciated regarding the carbs and keeping it at idle.

thanks

[05c50]

Sounds like a classic case of "gunk in the carbs". First check the condition of the tank, it should be clean.... no spotless. Any contaminates like rust or stale gas will cause problems later on. Next, remove the carbs and completely clean all jets, passageways and floats and bowl interiors. You probably won't need to replace any hard parts (jets, needles, floats), but may need a few o rings and bowl gaskets. Be very meticulous when you clean.

.......Paul

[arncruz]

Paul,
Do you recommend a carb soak and if so what kind?  Or do you recommend I take it all apart?  thanks

[05c50]

Depending on the condition, you may not need to soak the carbs. If you do end up soaking them, you should dis assemble them so as not to destroy any of the soft parts and to completely access all of the passageways.If you could post a picture of the carbs with the bowls off, we may be able to get an idea how bad they are. Have you checked the tank?

..........Paul

[harisuluv]

The float pins are just metal pins that physically hold the float at a point to pivot on.  I'm not sure you mean this, I have a feeling you might mean the valves.  The pin could be phsycailly welded in place and it wouldn't matter in regards to functionality of the float, the float can pivot independent of it.  Of course there are obvious reasons why you don't want the pin welded in place...

Adjusting the idle isn't really adjusting a specific idle range.  All the idle adjust screw does is change where the position is set to when you let go of the throttle.  Basically holding the throttle and just setting the idle screw very high are essentially the same thing. 

Your overflow problem with #1 could be many things but is probably a sticking/dirty valve/float height issue.  Most of the symptoms you listed point to dirty idle/slow speed jets.

[arncruz]

Here are some pics of the carb bottom end.  I removed the main jet and soaked it.  I'm not too sure how to clean the slow jet though.  I can't seem to remove them.  The top end of the carbs look clean and untouched so I did not attempt to take that apart.  any suggestions on cleaning the slow jets?

[harisuluv]

The slow jets are not easily removable due to EPA regulations at the time.  They are not screwed in, rather, pressed in, what Honda dubs "friction fit." 

To remove them you simply need to grab hold of them with something and coax them out.  Slight turn with vice grips might break the initial fit, then just pull it out.  You want to maybe use a non serrated jaw vice grips or something between the jet and vice grips to prevent marring of the brass.  I use a piece of scrap leather that helps.  Try to come straight out otherwise you will bend the jet and can distort the internals with a kink.

[cb650]

The slow jets will "twist" out.  Be genital.  Be sure to clean the main jet imulsion tubes too.

[arncruz]

Thanks harisuluv, I read this AFTER doing this - I took a syringe and injected some carb cleaning solution into the slow jet.  It pooled initially but then gave way whatever was obstructing it.  I injected more carb clean solution and it appeared to go in pretty easily now and no longer pooling.  I put the carbs back in the motorcycle.  Then I changed out the airbox for some pod air filters I had from a previous motorcycle.  I crossed my fingers and pressed the start button.  To my surprise, the engine started right up.  I did not need to keep the choke open and actually backed off on the idle.  It now holds an idle BUT it seems to be revving at a higher idle.  I took the bike for a spin around the block and got it up to 3rd gear.  when I went to a stop, the engine was still idling at a high RPM.  Do you have any suggestions?  thanks

[harisuluv]

That can be a sign of running lean.  Similar to how you start to run out of gas and suddenly your rpms go up and stay there before just suddenly dying from lack of fuel. 

What kind of exhaust and air filter system do you have?  More importantly, how far away from stock?

[alacrity]

Fwiw.  I disagree with cb650s suggestion just above.   In fact, I would recommend against being genital at any time in your garage.  On the other hand, being gentle with little carb arts is always a great idea.   ;-)


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[arncruz]

harisuluv,
I have a 4 into 2 exhaust.  The stock airbox was fine but I need to replace the rubber that goes to the carbs because several are torn.  So while i'm waiting for the replacements in the mail, I put some K&N pod air filters that I had from a previous bike.  How do I get it so it does not run lean? This means I need to either increase the fuel or decrease the airflow, Right?

[harisuluv]

Well, you have pods now.  Unless you are going to run with pods, it's pointless to tune it at all.  Pods and stock airbox are polar opposites.  To get it to run right would involve jet changes and needle clip position change or shim.  Sounds like you are waiting on parts to put the aribox back on so, I would wait til then if I were you.  You might find that all your problems go away.

[cb650]

Fwiw.  I disagree with cb650s suggestion just above.   In fact, I would recommend against being genital at any time in your garage.  On the other hand, being gentle with little carb arts is always a great idea.   ;-)


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Where is the intention checker?