'81 cb650c idle jets, how do i clean them?

If it's broken or just needs tweaked

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Todd Richards
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Re: '81 cb650c idle jets, how do i clean them?

Postby Todd Richards » Wed May 09, 2012 11:57 am

glad to help out!

as i said earlier, when i went thru this that nasty little bugger gave me a few fits, till i got it right... then smooth as silk ever since!

just be sure that the burbon and cigar are after the celebratory run/ride :wink:

nashbuilder
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Re: '81 cb650c idle jets, how do i clean them?

Postby nashbuilder » Wed May 09, 2012 8:00 pm

Celebration fail...put carbs on started it up and it was idling a little high 2500RPM, I gave it a little throttle revved it to 5000 rpm's and let the throttle go. When I let it go the engine continued to stay revved at 5000rpms. Did this before I rebuilt the carbs. Any thoughts on this problem?

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Volker_P
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Re: '81 cb650c idle jets, how do i clean them?

Postby Volker_P » Thu May 10, 2012 1:37 am

Throttle goes back at all (spring)? What happens if you turn out the manual idle knob?
Air leak at the carb boots?
Poor synchronization of throttle butterflies?
Runs permanently on all four at all (headers equally hot)?
Cosky's great (free) online manual: http://cosky0.tripod.com

forum links to common technical issues

If you really like this site and you would not like to see it vanish soon, have a look there: Urgent: Future of HondaCB650.com Forum

Todd Richards
Posts: 79
Joined: Tue Jan 17, 2012 2:52 pm

Re: '81 cb650c idle jets, how do i clean them?

Postby Todd Richards » Thu May 10, 2012 5:58 am

check your idle adjustment knob (if you have not already) and throttle butterflies for free/ease of movement throughout operating range

Do you recall during your rebuild, if the throttle adjustment screw was set such that the butterflies were just slightly open, or was there a huge gap?

Todd Richards
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Joined: Tue Jan 17, 2012 2:52 pm

Re: '81 cb650c idle jets, how do i clean them?

Postby Todd Richards » Thu May 10, 2012 6:00 am

take a look here:

http://nighthawk-forums.com/index.php/topic,2962.0.html

there is also another topic on throttle plate bench sync. to help out wit the initial setting of idle adjustment screw.

Regards

nashbuilder
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Re: '81 cb650c idle jets, how do i clean them?

Postby nashbuilder » Thu May 10, 2012 9:37 am

The boots all looked fine, the throttle plates all moved together (on the bench) , the throttle is snapping back no problem, the throttle adjuster is all the way out, the idle screw on each carb are at 2 1/4 turns out. The throttle butterflies were set at just slightly open where one of the 4 jet holes was showing.

That link requires a login so I will sign up and see if that helps. If there is anything else that comes to mind I really appreciate all tips...im almost at my wits end with this project.

Todd Richards
Posts: 79
Joined: Tue Jan 17, 2012 2:52 pm

Re: '81 cb650c idle jets, how do i clean them?

Postby Todd Richards » Thu May 10, 2012 10:00 am

just curious... did you have the choke at full when the idle jumped to 2500 RPM? The bikes are set up to increase to high idle very quickly upon startup.

if you were to start the bike up again, from cold start, check to see that the engine rpm's advance to the factory specification (i believe this should be somewhere around 2000 rpm? then hold steady there.)

if it begins to advance further, towards the 5k mentioned earlier, quickly move the choke lever to the full off position, and see if the rpms drop? There is a chance that the bendable tab that controls your high idle adjustment is itelf out of adjustment. When the choke is set to full on, this tab basically rotates into position & overides/opens the throttle butterflies to allow more fuel to the mixture.

With your carburetors removed, you can verify this by setting the carburetor to full choke and checking the throttle butterflies to see if they appear to have opened?

Were you able to download the PDF from McGregors carburetor cleaning services? I believe that there is some information there regarding setting/adjusting the fast idle tab.

I hope this helps... keep me posted.

nashbuilder
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Re: '81 cb650c idle jets, how do i clean them?

Postby nashbuilder » Thu May 10, 2012 11:32 am

I used that McGregors PDF when I did the rebuild...however I did not read the entire 36 pages. I know that when the carbs were on the bench I pulled the choke and the throttle plates did open slightly.

I will spend a little more time on it tonight and report back.

Todd Richards
Posts: 79
Joined: Tue Jan 17, 2012 2:52 pm

Re: '81 cb650c idle jets, how do i clean them?

Postby Todd Richards » Thu May 10, 2012 11:48 am

Do you have a service manual that states the gap size? you'll need this to determine if yours needs adjusted.

There is a procedure for adjusting this, if it need be? I can get it for you, just let me know.

Todd Richards
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Re: '81 cb650c idle jets, how do i clean them?

Postby Todd Richards » Fri May 11, 2012 7:25 am

Ok, so... how did it go last night?

nashbuilder
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Re: '81 cb650c idle jets, how do i clean them?

Postby nashbuilder » Sat May 12, 2012 10:25 am

So its my Anniversary weekend so I am not able to work much more on it. However I did take them back off the bike and did the best I can to sync the throttle plates on the bench. I do have a friend that has a vacuum sync set so we are hoping to get that on it next week. I will let you know how that goes.

I appreciate all the advise, its good to have a site where someone actually knows the bike I am working on. So many people have no idea about the bike but act as if they do. Thanks

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Volker_P
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Re: '81 cb650c idle jets, how do i clean them?

Postby Volker_P » Sat May 12, 2012 10:40 am

If you turn out the throttle knob, are all four throttle butterflies really closed? If carb boots are tight, no way then to get air into the engine for 5000rpm with the manual knob completely out.
So this is why I think you should take care for the synchronization again.
All four butterflies must be really close and open simultaneously to the same tiny gap when you turn in the manual idle adjust knob.
Maybe a good idea to fix the pistons a bit lifted so you can check out for tiny gaps against the light. Note that #2 (with accelerator pump) is not adjustable and serves as the reference.

Note that vacuum sync only works reliably when everything else is set all right. The visual sync with tiny gaps should be sufficient for reasonable idle and throttle response for all non-racing applications.
Cosky's great (free) online manual: http://cosky0.tripod.com

forum links to common technical issues

If you really like this site and you would not like to see it vanish soon, have a look there: Urgent: Future of HondaCB650.com Forum

nashbuilder
Posts: 48
Joined: Thu Mar 08, 2012 8:30 pm

Re: '81 cb650c idle jets, how do i clean them?

Postby nashbuilder » Tue May 15, 2012 12:17 pm

So I am following all the instruction on McGregors Carb Rebuild PDF and I am having a problem. I have worked on it twice now and still the same thing.

When I fit the E string under the plate everything is fine. The next step is to remove the e string and turn the main throttle knob out so that the plates just cover the front most hole ( not the pilot hole). When I do this the plates will not close that far and bind on the carb body. Besides that everything else looks great. Thoughts on the binding?

Todd Richards
Posts: 79
Joined: Tue Jan 17, 2012 2:52 pm

Re: '81 cb650c idle jets, how do i clean them?

Postby Todd Richards » Tue May 15, 2012 12:38 pm

make sure the carburetors are located on a flat surface when you secure them to the racks, keep in mind that you build them up, initially as 2 sets of 2 carburetors, then bring them together as one set of 4.

from what i recall, when you install the rear screws the intakes of each carb should be on the flat mounting surface and each other?(i may have this completely backward) what i did was install the carburetor mounting screws as stated in the service manual, just hand tight to begin with, while checking that the carb & intake linkage operates smoothly through out its operationg range. The rack screws that secure the carbs, are tightened and torqued in a sequence. follow this procedure to the letter, checking each time you torque a screw that no binding is present, in both the choke and intake butterflies.

from what i recall, the rear rack (choke) is installed first. then the front rack (intake) is last.

Do you have a service manual for reference?

small steps, checking for free, non binding movement of choke and intake butterflies every time you tighten a screw.

I hope this helps, If you dont have a service manual, i may be able to scan and attach the pages you need.

Todd Richards
Posts: 79
Joined: Tue Jan 17, 2012 2:52 pm

Re: '81 cb650c idle jets, how do i clean them?

Postby Todd Richards » Tue May 15, 2012 1:02 pm

i just re-read you post and wanted to be sure i understand you completely:

Upon Assembly:

when you are installing the sychronizing screws and lock nuts for carburetors 1, 3 & 4 be sure they are installed such that the intake for each is open a little bit when the idle adjustment screw is fully disengaged and the throttle butterfly for the #2 carb is fully closed. this method will give you the adjustment room you need to close them for the bench sync.

1)Throttle screw fully disengaged, correct?
2) Now use throttle screw to set #2 carburetor only (it is the base)
3) use adjusting screw specific to each carburetor it is attached to , to adjust it's intake, with string


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