79 cb650 carb jetting question

If it's broken or just needs tweaked

Moderators: Volker_P, tidd650

emy111
Posts: 9
Joined: Tue Mar 31, 2009 12:09 pm

79 cb650 carb jetting question

Postby emy111 » Tue Mar 31, 2009 12:47 pm

hi... i have a 79 cb650. i am in the process of putting pod filters on my bike.

i am keeping the stock exhaust.

i am having a hard time finding aftermarket main jets, slow jets,... anything for 79 model...

in this other post:
viewtopic.php?f=4&t=671&p=5734&hilit=carb+jets#p5734

jochild... you said that you increased your main jets to 95's...

and Pinhead... you said you're running 102.5...

where did you guys get your main jets and other stuff from? and what size do you think i should increase to if the original main jets are 90...?

post a rely or email me at emy111@gmail.com

thanks!!!!!!!!!

emy111
Posts: 9
Joined: Tue Mar 31, 2009 12:09 pm

Re: 79 cb650 carb jetting question

Postby emy111 » Mon Nov 23, 2009 10:49 pm

for anyone wanting to know what jetting to run with pod filters, i took the sweat and tears to figure it all out. this is for 79 and 80 only!!! just for reference, my bike was perfectly running, stock condition before i decided to rip it apart and put pods on. i didn't know what i was getting into. here is the formula that works great for me. (i live in Philadelphia...)

my set up now is:
- Emgo pod filters
- Mac 4-1 exhaust
- 120 main jets
- 42 slow jets
- air mixture screws set to 2 turns out

my bike runs fuckin awesome. no bogging at low rpm, smooth linear power all the way to redline. def way faster now, compared to how it was stock. it seriously took me about 2 months of trial and error with different jet combinations, but I finally got it right. it sounds sick as fuck too with the pods and mac 4-1 exhaust. my plugs look great too, nice light brown color, not lean, not rich... it's just right.

oh, and i bought all my jets from either:
A) http://www.jetsrus.com/
B) http://www.siriusconinc.com

you can read some more info about my build / pod filters here:
http://www.flickr.com/photos/10396190@N04/3433248288/

and see random other pics of my bike on the rest of my flickr:
http://www.flickr.com/photos/10396190@N04/

User avatar
Volker_P
Posts: 5508
Joined: Mon Mar 06, 2006 1:53 am
Location: southern Germany

Re: 79 cb650 carb jetting question

Postby Volker_P » Tue Nov 24, 2009 3:48 am

Thanks for the great info! :D
I think the pod filter guys will canonize you soon. :lol:
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

Shindokwan
Posts: 8
Joined: Mon May 23, 2011 10:14 am
Location: Michigan

Re: 79 cb650 carb jetting question

Postby Shindokwan » Mon May 23, 2011 10:20 am

Hello, I am new to this forum and wanted to ask, you said you jetted your carbs using a 42 slow jet and a 120 main jet, what are the stock jets? Just want to know how much of a difference the jets you used are from factory.

Thanks!

adam80
Posts: 11
Joined: Mon May 09, 2011 10:45 pm
Location: Auburn, AL

Re: 79 cb650 carb jetting question

Postby adam80 » Mon May 23, 2011 8:37 pm

I'm fairly sure the stock main jet is #90 (0.90mm) and the slow jet is #35.

I'm in the process of installing K&N pod filters myself with the stock exhaust; I'll post a thread later to let everyone know how it goes :)
1980 CB650 Custom

Shindokwan
Posts: 8
Joined: Mon May 23, 2011 10:14 am
Location: Michigan

Re: 79 cb650 carb jetting question

Postby Shindokwan » Mon May 23, 2011 8:43 pm

I guess I didn't read the first post of this thread fully, it says for a 79 and 80 model only, I am working on a 1982. Does anybody know what the stock slow and main jets are for this year and also what good upgrade would be if I am converting to pod filters but keeping stock exhaust?? Any help would be greatly appreciated and I may start a new post for this question, I am really curious, thanks!

User avatar
Volker_P
Posts: 5508
Joined: Mon Mar 06, 2006 1:53 am
Location: southern Germany

Re: 79 cb650 carb jetting question

Postby Volker_P » Tue May 24, 2011 2:44 am

Welcome here. Mike!

1981 CV carbs have 120 mains. Probably the same for 1982. According to the Question on Idle/Pilot Jet thread, you should have 35 pilot jets.

1982 should have mains and idle jets screwed in, so perfect for what you are planning. One can say that CV carbs are less susceptible to pod filters, so certainly not a change from 92 to 120 like for piston carbs. But sorry, not aware of data. You may try to search for it in the forum.

Playing around with jetting will take some time, so why do you want to do all this if you are going to sell the bike soon? I would not think a filter or exhaust change will bring back the money. I even expect this being counterproductive on a low miles and still close to stock bike.
If you really want to get $2000, I assume you should have all stock parts in nice condition (either on or together with the bike).
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

Shindokwan
Posts: 8
Joined: Mon May 23, 2011 10:14 am
Location: Michigan

Re: 79 cb650 carb jetting question

Postby Shindokwan » Tue May 24, 2011 6:34 am

I was only toying with the idea of upgrading jets when I was cleaning the carbs, I am still debating on selling this bike it is such a fun bike!! I probably will end up keeping it stock, I was just curious on jetting in case I decide to keep it. Based on the thread I was reading it seemed like it was fairly simple to upgrade the jets. Thanks so much for the info! I am sure I will be asking more questions, this is a great forum!!

Take care!

tinbirdmotorcycles
Posts: 1
Joined: Mon Mar 13, 2017 5:15 am

Re: 79 cb650 carb jetting question

Postby tinbirdmotorcycles » Mon Mar 20, 2017 5:07 am

emy111 wrote:for anyone wanting to know what jetting to run with pod filters, i took the sweat and tears to figure it all out. this is for 79 and 80 only!!! just for reference, my bike was perfectly running, stock condition before i decided to rip it apart and put pods on. i didn't know what i was getting into. here is the formula that works great for me. (i live in Philadelphia...)

my set up now is:
- Emgo pod filters
- Mac 4-1 exhaust
- 120 main jets
- 42 slow jets
- air mixture screws set to 2 turns out

my bike runs fuckin awesome. no bogging at low rpm, smooth linear power all the way to redline. def way faster now, compared to how it was stock. it seriously took me about 2 months of trial and error with different jet combinations, but I finally got it right. it sounds sick as fuck too with the pods and mac 4-1 exhaust. my plugs look great too, nice light brown color, not lean, not rich... it's just right.

oh, and i bought all my jets from either:
A) http://www.jetsrus.com/
B) http://www.siriusconinc.com

you can read some more info about my build / pod filters here:
http://www.flickr.com/photos/10396190@N04/3433248288/

and see random other pics of my bike on the rest of my flickr:
http://www.flickr.com/photos/10396190@N04/


Hey!

I know this is an old post, but I will try anyway. Thanks for the straight forward info:)! I have a 1980 and I think it is the same carbs as yours. I´m going to try these recipie out:)...I have 4 to 2 system with a quite open muffler. Do you think it can work:)?

User avatar
tario
Posts: 166
Joined: Sat Mar 07, 2015 2:26 pm

Re: 79 cb650 carb jetting question

Postby tario » Tue Mar 21, 2017 8:35 am

It looks like 116 mains and 38 pilots are about right for that. Cafe racers united has a guide to rejetting that helped me come up with these rough numbers. 4 to 1 being added means 4 jet sizes up. Your exhaust needs 2 sizes up. A jet size is 2 or 2.5 from what i remember (depends on the brand).

To rejet you should pick up 114, 116, and 118 mains. Then 36, 38, and 40 pilots. For every 2000' above sea level you can knock another 2 off each of those numbers. If you can find an old set to drill out and play with you might be able to get a better idea of size. I've heard certain bits are better for drilling.(and there are charts online that tell you the jet size to drill size conversion.) The jets do have a taper so you should buy a new set once you figure out a rough size. ...then buy a second set when you figure out how rich/lean you are running.

EDIT; I was double checking the article and it actually meant 2 in the jet number. So a change of 2 sizes means from 118 to 120. I still think the above numbers might be about right. Their guide doesn't change things enough based on the rejetting I've seen for these bikes and carbs. It looks like jet sizes make exponential changes too, so the bigger the stock jets are the smaller the increase. (makes sense, Pi x r ^2) Of course all of this depends on the air speed in a particular carb set. Air velocity is a component in the venturi effect. I wish I could find a basic formula for this...
1979 cb650
1980 cb650

Chief78
Posts: 6
Joined: Sat Jul 20, 2019 1:30 pm

Re: 79 cb650 carb jetting question

Postby Chief78 » Sun Aug 04, 2019 10:42 am

Hey guys. Great information. I realize this topic is untouched for quite some time now but I feel like I me to respond anyways. I have looked on cafe racers United to use that rejetting tool but cannot find it. I have a 1979 CB650 with 4 into 1 header and 2 and 1/2 inch straight through Muffler. I took the back half of the airbox off and put a spectre cold air intake filter on so I could avoid using pods but still get good airflow. Any help would be appreciated. I hope you guys bikes are still running Tip Top


Return to “Technical Discussion”

Who is online

Users browsing this forum: No registered users and 42 guests