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81 CB650 carb problem


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#1 easyrider75

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Posted 08 July 2012 - 04:45 PM

Hello, I'm building a 81 CB650 chopper. Not the best starting platform but I had to take this or nothing. Bike ran fair for being rode in january, and siting for who knows how long, 17000 on the clock and all there. Closer inspection revealed a blown head gasket, no big deal, parts are cheap. Anyhow, I went to the pod air filters, rebuilt the carbs (ultrasonic cleaned, new jets, gaskets, o-rings), and suprise! they don't work correctly. They idle great but as soon as you want to go they crap out and the bike dies. When riding the bike it would not run well unless you had the choke pulled, then it ran not to bad. So,im looking for some help in getting these carbs to work. They are CV style, I was hoping to get rid of the auto petcock, as i don't feel its necessary being as you have a fuel shut off on the tank.

#2 Bonehead9

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Posted 08 July 2012 - 06:37 PM

It's too lean if you have to have the choke out to make it run.

You mentioned pods....did you also modify the exhaust?

Did you put in bigger jets or use the stock ones?
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#3 easyrider75

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Posted 08 July 2012 - 08:09 PM

It's too lean if you have to have the choke out to make it run.

You mentioned pods....did you also modify the exhaust?

Did you put in bigger jets or use the stock ones?



I put the bigger jet in the main, the idle jet is permanent unless you know magic(or machining), exhaust is strait no baffles, cut off right behind the crossover(4 individual). When i rebuit the carbs i do believe they all run off of one central accelerator pump(the diaphram seemed worn but functional) is this true? also the slides don't seem to slide very much,which leads me to think that i have a lack of vaccum, I took a lot of plastic canister type shit off and I think this may be hurting me.

#4 Bonehead9

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Posted 09 July 2012 - 07:31 AM

Do you have a manual?.....really....it'll help with a lot of problems.

Not real sure on the CB650....hopefully someone else will chime in.

Definitely check for vacuum leaks. Make sure all the little hoses you disconnected are plugged. Use WD40 or carb cleaner to spritz around the carb connection boots/flanges...be very careful if you use carb cleaner VERY FLAMMABLE......if the motor revs raise from idle when you spritz, you got a leak.

Might be worth the time to pull the slides and make sure...absolutely sure....they aren't hanging up somewhere. Pull them, rub them down with steel wool, clean them well.

I'm just telling you what I would do....I'm no pro by any stretch of the imagination.
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#5 Dieselchanic

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Posted 09 July 2012 - 08:28 AM

Sounds like either your slides aren't coming up as mentioned, your accelerator pumps not working, or your jets could be loose or too small or who knows. Take em back apart and double check everything is tight and looks normal. Sounds as though it's leaning out immediately tho so that would suggest the accelerator pump or small jets. Loose jets or sticky slides would cause it to flood....

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#6 Powderburn

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Posted 09 July 2012 - 09:20 AM

Sounds alot like you have pod filters that are sealing the port at the top of the inlet of the carbs..

this happens alot. That port needs to be open to atmospheric pressure..

Pull off the filters and see if it improves dramatically if so look in the filter and see if it blocks it when installed.

You can cut a notch in some of em and still filter air. Some no.. Seen this with places that sell cheaper filters and

just go by filter side diameter and figuire its ok.. THERE ROUND OR FLATSLIDE filters.. were it doesn't matter

#7 nitroeagle

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Posted 13 July 2012 - 09:09 PM

I have an '82 cb650 with the same carbs. I rebuilt mine also, & when I was done it would idle fine, but as soon as I hit the gas, nothing. Stupid me, it turned out I set the floats on pins wrong so they wouldn't open. Hey we're human right? You mentioned taking plastic stuff off. I know there's a "tee" between #1 & 2, and another between #3 & 4. I know this can cause some issues. They're rubber & not cheap, like $40 a piece. I was able to find some small plastic tees in work that fit in the holes, as the stock set up is rubber & fits over the holes. You're right on the accelerator pump, one for the whole set up. I'm definitely not an expert, still playing with mine. Hope it helps a little. I have pods on mine & am still tuning it. I put in 125 main jets, seems better now.