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 jet sizes for cb650 custom 
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Joined: Mon Jul 23, 2012 4:20 am
Posts: 10
Post jet sizes for cb650 custom
I have recently purchased an 81 cb650 custom and i need to purchase slow jets for it. My carb guy told me to purchase 2 sizes above stock and im not sure what size to get. im new to the 4 cylinder as my previous bike is a 71 cb350. any help would be appreciated. also where to get would be awesome too. excited to be back driving a 650!


Mon Jul 23, 2012 4:33 am
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Joined: Mon Apr 30, 2012 3:17 am
Posts: 132
Location: South east Michigan
Post Re: jet sizes for cb650 custom
Is this a trick question? You can't get the slow jets out of the 44a carbs (at least without destroying them) I don't know of anywhere to get replacement press in jets. My best answer was to get a set of 44c ('82) carbs and now all is good with the world.


Mon Jul 23, 2012 4:39 am
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Joined: Fri Mar 03, 2006 7:20 am
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Location: Denver CO USA
Post Re: jet sizes for cb650 custom
Some here did get them out. Thread with pics. I'm sure Volker will post the link. He remembers where all the threads are. :lol:

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Mon Jul 23, 2012 5:50 am
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Joined: Mon Apr 30, 2012 3:17 am
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Location: South east Michigan
Post Re: jet sizes for cb650 custom
Just wondering, Why did he tell you to go up 2 sizes on the lets? I believe the jets in my 650 are 38s so I'm guessing that would mean he wants 42s. I got a set of carbs off the internet with 42s in them and my bike ran like poop. My bike now has 38/105 jets and is running great. I'm only a little above sea level and have stock air box and pipes.


Mon Jul 23, 2012 8:06 am
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Location: southern Germany
Post Re: jet sizes for cb650 custom
cb650 wrote:
Some here did get them out. Thread with pics. I'm sure Volker will post the link.

Correct, here is the link:
viewtopic.php?f=4&t=4492&start=66

cb650 wrote:
He remembers where all the threads are. :lol:

No, he is too old for that now.
But he has an internal links list

This list may also be found easily in my signature/footer. :wink:

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Mon Jul 23, 2012 10:25 am
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Joined: Mon Jul 23, 2012 4:20 am
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Post Re: jet sizes for cb650 custom
Bike has just straight pipes and a k&n air filters. Idles ok but runs like poop in midrange and screams on the top end. We went up on Jet from stock but still isnt getting enough fuel. So go with 42s? Where is a good place to purchase?


Mon Jul 23, 2012 10:40 am
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Joined: Mon Apr 30, 2012 3:17 am
Posts: 132
Location: South east Michigan
Post Re: jet sizes for cb650 custom
this may help

http://www.siriusconinc.com/pro-detail.php?pid=&product_id=1109

in case you want to try raising the needle

http://www.siriusconinc.com/pro-detail.php?pid=&product_id=2188

by the way,a #78 drill (.016")will give you aprox a 41 jet size


Mon Jul 23, 2012 11:37 pm
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Location: southern Germany
Post Re: jet sizes for cb650 custom
Welcome here! :D

hedlund65 wrote:
Bike has just straight pipes and a k&n air filters. Idles ok but runs like poop in midrange and screams on the top end.

Sounds like idle seems all right. Idle jets play no role in the upper regimes any more. You have to lift the needles or/and use larger mains in this case. You still may try out with a bit of choke if it really needs more fuel before you decide what to do next.
Make sure all four plugs look equal and are not more than just slightly white.

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Tue Jul 24, 2012 1:04 am
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Joined: Mon Jul 23, 2012 4:20 am
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Post Re: jet sizes for cb650 custom
So is 35 stock on these carbs?


Tue Jul 24, 2012 11:53 am
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Location: southern Germany
Post Re: jet sizes for cb650 custom
1981 Custom means CV carbs, carb number starts VA44, stock mains are are 117/120, not sure for idle jets, about 40 I guess.

35 is stock for the PD (1979/80) carbs.

As written, you have no idle jet problem as your idle seems all right.
Check out what I did write and care for the needles or mains instead if required.

cgswss10 wrote:
My bike now has 38/105 jets and is running great. I'm only a little above sea level and have stock air box and pipes.

This sounds like 1979/80 PD carbs, right? Completely different building site!

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Tue Jul 24, 2012 1:44 pm
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Joined: Mon Apr 30, 2012 3:17 am
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Location: South east Michigan
Post Re: jet sizes for cb650 custom
no I'm running 44c carbs ('81 custom with '82 carbs)


Tue Jul 24, 2012 7:17 pm
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Joined: Mon Jul 23, 2012 4:20 am
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Post Re: jet sizes for cb650 custom
So like u said volker, a little choke going around the corners is all it needed. Being amateurs we are we grabbed a #78 bit and drilled it out causing the bike to load up and run like shit. Replaced plugs and when we got it to top end ran well, but lower rpms it's bad. So we tapped the jet and pulled it and it was a 35. Now do I replace them with 35s again? Before we messed with it, the bike was running "cold blooded, but once u got it to about 4500+ rpms it ran awesome. Pipes are cut off by foot pegs and have 2 k&n filters on carbs.


Thu Jul 26, 2012 9:10 pm
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Joined: Mon Apr 30, 2012 3:17 am
Posts: 132
Location: South east Michigan
Post Re: jet sizes for cb650 custom
how about here

http://www.siriusconinc.com/search_result.php?make=1&model=&part=1&partno=&x=31&y=18&search=search&start=250


Thu Jul 26, 2012 10:03 pm
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Joined: Mon Apr 30, 2012 3:17 am
Posts: 132
Location: South east Michigan
Post Re: jet sizes for cb650 custom
By the way, after you pull those jets, don't throw them away. A little silver solder and some number bits and you can make some experimental jets

drill size 83 gives a 31 jet
drill size 82 gives a 32 jet
drill size 81 gives a 33 jet
drill size 80 gives a 35 jet
drill size 79 gives a 37 jet


Thu Jul 26, 2012 10:15 pm
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Joined: Mon Jul 23, 2012 4:20 am
Posts: 10
Post Re: jet sizes for cb650 custom
That link is for screw in jets I need press in. Should I stay with the 35s? The guy who "fixed" the carbs earlier this year said he went one size over stock, but the jets that are in say 35 so I'm wondering if he drilled them out.


Thu Jul 26, 2012 10:19 pm
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